Ubuntu Manpage: stress-ng - stress "next generation", a tool to load and stress a computer system

Provided by: stress-ng_0.17.06-1build1_amd64

NAME

       stress-ng - stress "next generation", a tool to load and stress a computer system

SYNOPSIS

       stress-ng [OPTION [ARG]] ...

DESCRIPTION

stress-ng will stress test a computer system in various selectable ways. It was designed
to exercise various physical subsystems of a computer as well as the various operating
system kernel interfaces. stress-ng also has a wide range of CPU specific stress tests
that exercise floating point, integer, bit manipulation and control flow.

stress-ng was originally intended to make a machine work hard and trip hardware issues
such as thermal overruns as well as operating system bugs that only occur when a system is
being thrashed hard. Use stress-ng with caution as some of the tests can make a system run
hot on poorly designed hardware and also can cause excessive system thrashing which may be
difficult to stop.

stress-ng can also measure test throughput rates; this can be useful to observe
performance changes across different operating system releases or types of hardware.
However, it has never been intended to be used as a precise benchmark test suite, so do
NOT use it in this manner.

Running stress-ng with root privileges will adjust out of memory settings on Linux systems
to make the stressors unkillable in low memory situations, so use this judiciously. With
the appropriate privilege, stress-ng can allow the ionice class and ionice levels to be
adjusted, again, this should be used with care.

One can specify the number of processes to invoke per type of stress test; specifying a
zero value will select the number of processors available as defined by
sysconf(_SC_NPROCESSORS_CONF), if that can't be determined then the number of online CPUs
is used. If the value is less than zero then the number of online CPUs is used.

OPTIONS

General stress-ng control options:

--abort
this option will force all running stressors to abort (terminate) if any other
stressor terminates prematurely because of a failure.

--aggressive
enables more file, cache and memory aggressive options. This may slow tests down,
increase latencies and reduce the number of bogo ops as well as changing the
balance of user time vs system time used depending on the type of stressor being
used.

-a N, --all N, --parallel N
start N instances of all stressors in parallel. If N is less than zero, then the
number of CPUs online is used for the number of instances. If N is zero, then the
number of configured CPUs in the system is used.

-b N, --backoff N
wait N microseconds between the start of each stress worker process. This allows
one to ramp up the stress tests over time.

--change-cpu
this forces child processes of some stressors to change to a different CPU from the
parent on startup. Note that during the execution of the stressor the scheduler may
choose move the parent onto the same CPU as the child. The stressors affected by
this option are client/server style stressors, such as the network stressors (sock,
sockmany, udp, etc) or context switching stressors (switch, pipe, etc).

--class name
specify the class of stressors to run. Stressors are classified into one or more of
the following classes: cpu, cpu-cache, device, gpu, io, interrupt, filesystem,
memory, network, os, pipe, scheduler, signal and vm. Some stressors fall into just
one class. For example the 'get' stressor is just in the 'os' class. Other
stressors fall into more than one class, for example, the 'lsearch' stressor falls
into the 'cpu', 'cpu-cache' and 'memory' classes as it exercises all these three.
Selecting a specific class will run all the stressors that fall into that class
only when run with the --sequential option.

Specifying a name followed by a question mark (for example --class vm?) will print
out all the stressors in that specific class.

--config
print out the configuration used to build stress-ng.

-n, --dry-run
parse options, but do not run stress tests. A no-op.

--ftrace
enable kernel function call tracing (Linux only). This will use the kernel debugfs
ftrace mechanism to record all the kernel functions used on the system while
stress-ng is running. This is only as accurate as the kernel ftrace output, so
there may be some variability on the data reported.

-h, --help
show help.

--ignite-cpu
alter kernel controls to try and maximize the CPU. This requires root privilege to
alter various /sys interface controls. Currently this only works for Intel P-State
enabled x86 systems on Linux.

--interrupts
check for any system management interrupts or error interrupts that occur, for
example thermal overruns, machine check exceptions, etc. Note that the interrupts
are accounted to all the concurrently running stressors, so total count for all
stressors is over accounted.

--ionice-class class
specify ionice class (only on Linux). Can be idle (default), besteffort, be,
realtime, rt.

--ionice-level level
specify ionice level (only on Linux). For idle, 0 is the only possible option. For
besteffort or realtime values 0 (highest priority) to 7 (lowest priority). See
ionice(1) for more details.

--iostat S
every S seconds show I/O statistics on the device that stores the stress-ng
temporary files. This is either the device of the current working directory or the
--temp-path specified path. Currently a Linux only option. The fields output are:

Column Heading Explanation
Inflight number of I/O requests that have been issued to the device driver
but have not yet completed
Rd K/s read rate in 1024 bytes per second
Wr K/s write rate in 1024 bytes per second
Dscd K/s discard rate in 1024 bytes per second
Rd/s reads per second
Wr/s writes per second
Dscd/s discards per second

--job jobfile
run stressors using a jobfile. The jobfile is essentially a file containing
stress-ng options (without the leading --) with one option per line. Lines may have
comments with comment text proceeded by the # character. A simple example is as
follows:

run sequential # run stressors sequentially
verbose # verbose output
metrics-brief # show metrics at end of run
timeout 60s # stop each stressor after 60 seconds
#
# vm stressor options:
#
vm 2 # 2 vm stressors
vm-bytes 128M # 128MB available memory
vm-keep # keep vm mapping
vm-populate # populate memory
#
# memcpy stressor options:
#
memcpy 5 # 5 memcpy stressors

The job file introduces the run command that specifies how to run the stressors:

run sequential - run stressors sequentially
run parallel - run stressors together in parallel

Note that 'run parallel' is the default.

--keep-files
do not remove files and directories created by the stressors. This can be useful
for debugging purposes. Not generally recommended as it can fill up a file system.

-k, --keep-name
by default, stress-ng will attempt to change the name of the stress processes
according to their functionality; this option disables this and keeps the process
names to be the name of the parent process, that is, stress-ng.

--klog-check
check the kernel log for kernel error and warning messages and report these as soon
as they are detected. Linux only and requires root capability to read the kernel
log.

--ksm enable kernel samepage merging (Linux only). This is a memory-saving de-duplication
feature for merging anonymous (private) pages.

--log-brief
by default stress-ng will report the name of the program, the message type and the
process id as a prefix to all output. The --log-brief option will output messages
without these fields to produce a less verbose output.

--log-file filename
write messages to the specified log file.

--log-lockless
log messages use a lock to avoid intermingling of blocks of stressor messages,
however this may cause contention when emitting a high rate of logging messages in
verbose mode and many stressors are running, for example when testing CPU scaling
with many processes on many CPUs. This option disables log message locking.

--maximize
overrides the default stressor settings and instead sets these to the maximum
settings allowed. These defaults can always be overridden by the per stressor
settings options if required.

--max-fd N
set the maximum limit on file descriptors (value or a % of system allowed maximum).
By default, stress-ng can use all the available file descriptors; this option sets
the limit in the range from 10 up to the maximum limit of RLIMIT_NOFILE. One can
use a % setting too, e.g. 50% is half the maximum allowed file descriptors. Note
that stress-ng will use about 5 of the available file descriptors so take this into
consideration when using this setting.

--mbind list
set strict NUMA memory allocation based on the list of NUMA nodes provided; page
allocations will come from the node with sufficient free memory closest to the
specified node(s) where the allocation takes place. This uses the Linux
set_mempolicy(2) call using the MPOL_BIND mode. The NUMA nodes to be used are
specified by a comma separated list of node (0 to N-1). One can specify a range of
NUMA nodes using '-', for example: --mbind 0,2-3,6,7-11

--metrics
output number of bogo operations in total performed by the stress processes. Note
that these are not a reliable metric of performance or throughput and have not been
designed to be used for benchmarking whatsoever. Some stressors have additional
metrics that are more useful than bogo-ops, and these are generally more useful for
observing how a system behaves when under various kinds of load.

The following columns of information are output:

Column Heading Explanation
bogo ops number of iterations of the stressor during the run.
This is metric of how much overall "work" has been
achieved in bogo operations. Do not use this as a
reliable measure of throughput for benchmarking.
real time (secs) average wall clock duration (in seconds) of the
stressor. This is the total wall clock time of all the
instances of that particular stressor divided by the
number of these stressors being run.
usr time (secs) total user time (in seconds) consumed running all the
instances of the stressor.
sys time (secs) total system time (in seconds) consumed running all the
instances of the stressor.
bogo ops/s (real time) total bogo operations per second based on wall clock
run time. The wall clock time reflects the apparent run
time. The more processors one has on a system the more
the work load can be distributed onto these and hence
the wall clock time will reduce and the bogo ops rate
will increase. This is essentially the "apparent" bogo
ops rate of the system.
bogo ops/s (usr+sys time) total bogo operations per second based on cumulative
user and system time. This is the real bogo ops rate
of the system taking into consideration the actual time
execution time of the stressor across all the
processors. Generally this will decrease as one adds
more concurrent stressors due to contention on cache,
memory, execution units, buses and I/O devices.
CPU used per instance (%) total percentage of CPU used divided by number of
stressor instances. 100% is 1 full CPU. Some stressors
run multiple threads so it is possible to have a figure
greater than 100%.
RSS Max (KB) resident set size (RSS), the portion of memory
(measured in Kilobytes) occupied by a process in main
memory.

--metrics-brief
show shorter list of stressor metrics (no CPU used per instance).

--minimize
overrides the default stressor settings and instead sets these to the minimum
settings allowed. These defaults can always be overridden by the per stressor
settings options if required.

--no-madvise
from version 0.02.26 stress-ng automatically calls madvise(2) with random advise
options before each mmap and munmap to stress the vm subsystem a little harder. The
--no-advise option turns this default off.

--no-oom-adjust
disable any form of out-of-memory score adjustments, keep the system defaults.
Normally stress-ng will adjust the out-of-memory scores on stressors to try to
create more memory pressure. This option disables the adjustments.

--no-rand-seed
Do not seed the stress-ng pseudo-random number generator with a quasi random start
seed, but instead seed it with constant values. This forces tests to run each time
using the same start conditions which can be useful when one requires reproducible
stress tests.

--oom-avoid
Attempt to avoid out-of-memory conditions that can lead to the Out-of-Memory (OOM)
killer terminating stressors. This checks for low memory scenarios and swapping
before making memory allocations and hence adds some overhead to the stressors and
will slow down stressor allocation speeds.

--oom-avoid-bytes N
Specify a low memory threshold to avoid making any further memory allocations. The
parameter can be specified as an absolute number of bytes (e.g. 2M for 2MB) or a
percentage of the current free memory, e.g. 5% (the default is 2.5%). This option
implicitly enables --oom-avoid. The option allows the system to have enough free
memory to try to avoid the out-of-memory killer terminating processes.

--oomable
Do not respawn a stressor if it gets killed by the Out-of-Memory (OOM) killer. The
default behaviour is to restart a new instance of a stressor if the kernel OOM
killer terminates the process. This option disables this default behaviour.

--page-in
touch allocated pages that are not in core, forcing them to be paged back in. This
is a useful option to force all the allocated pages to be paged in when using the
bigheap, mmap and vm stressors. It will severely degrade performance when the
memory in the system is less than the allocated buffer sizes. This uses mincore(2)
to determine the pages that are not in core and hence need touching to page them
back in.

--pathological
enable stressors that are known to hang systems. Some stressors can rapidly consume
resources that may hang a system, or perform actions that can lock a system up or
cause it to reboot. These stressors are not enabled by default, this option enables
them, but you probably don't want to do this. You have been warned. This option
applies to the stressors: bad-ioctl, bind-mount, cpu-online, mlockmany, oom-pipe,
smi, sysinval and watchdog.

--perf measure processor and system activity using perf events. Linux only and caveat
emptor, according to perf_event_open(2): "Always double-check your results! Various
generalized events have had wrong values.". Note that with Linux 4.7 one needs to
have CAP_SYS_ADMIN capabilities for this option to work, or adjust
/proc/sys/kernel/perf_event_paranoid to below 2 to use this without CAP_SYS_ADMIN.

--permute N
run all permutations of the selected stressors with N instances of the permutated
stressors per run. If N is less than zero, then the number of CPUs online is used
for the number of instances. If N is zero, then the number of configured CPUs in
the system is used. This will perform multiple runs with all the permutations of
the stressors. Use this in conjunction with the --with or --class option to specify
the stressors to permute.

--progress
display the run progress when running stressors with the --sequential option.

-q, --quiet
do not show any output.

-r N, --random N
start N random stress workers. If N is 0, then the number of configured processors
is used for N.

--sched scheduler
select the named scheduler (only on Linux). To see the list of available schedulers
use: stress-ng --sched which

--sched-prio prio
select the scheduler priority level (only on Linux). If the scheduler does not
support this then the default priority level of 0 is chosen.

--sched-period period
select the period parameter for deadline scheduler (only on Linux). Default value
is 0 (in nanoseconds).

--sched-runtime runtime
select the runtime parameter for deadline scheduler (only on Linux). Default value
is 99999 (in nanoseconds).

--sched-deadline deadline
select the deadline parameter for deadline scheduler (only on Linux). Default value
is 100000 (in nanoseconds).

--sched-reclaim
use cpu bandwidth reclaim feature for deadline scheduler (only on Linux).

--seed N
set the random number generate seed with a 64 bit value. Allows stressors to use
the same random number generator sequences on each invocation.

--settings
show the various option settings.

--sequential N
sequentially run all the stressors one by one for a default of 60 seconds. The
number of instances of each of the individual stressors to be started is N. If N
is less than zero, then the number of CPUs online is used for the number of
instances. If N is zero, then the number of CPUs in the system is used. Use the
--timeout option to specify the duration to run each stressor.

--skip-silent
silence messages that report that a stressor has been skipped because it requires
features not supported by the system, such as unimplemented system calls, missing
resources or processor specific features.

--smart
scan the block devices for changes S.M.A.R.T. statistics (Linux only). This
requires root privileges to read the Self-Monitoring, Analysis and Reporting
Technology data from all block devies and will report any changes in the
statistics. One caveat is that device manufacturers provide different sets of data,
the exact meaning of the data can be vague and the data may be inaccurate.

--sn use scientific notation (e.g. 2.412e+01) for metrics.

--status N
report every N seconds the number of running, exiting, reaped and failed stressors,
number of stressors that received SIGARLM termination signal as well as the current
run duration.

--stderr
write messages to stderr. With version 0.15.08 output is written to stdout,
previously due to a historical oversight output went to stderr. This option allows
one to revert to the pre-0.15.08 behaviour.

--stdout
all output goes to stdout. This is the new default for version 0.15.08. Use the
--stderr option for the original behaviour.

--stressors
output the names of the available stressors.

--syslog
log output (except for verbose -v messages) to the syslog.

--taskset list
set CPU affinity based on the list of CPUs provided; stress-ng is bound to just use
these CPUs (Linux only). The CPUs to be used are specified by a comma separated
list of CPU (0 to N-1). One can specify a range of CPUs using '-', for example:
--taskset 0,2-3,6,7-11

--temp-path path
specify a path for stress-ng temporary directories and temporary files; the default
path is the current working directory. This path must have read and write access
for the stress-ng stress processes.

--thermalstat S
every S seconds show CPU and thermal load statistics. This option shows average CPU
frequency in GHz (average of online-CPUs), the minimum CPU frequency, the maximum
CPU frequency, load averages (1 minute, 5 minute and 15 minutes) and available
thermal zone temperatures in degrees Centigrade.

--thrash
This can only be used when running on Linux and with root privilege. This option
starts a background thrasher process that works through all the processes on a
system and tries to page as many pages in the processes as possible. It also
periodically drops the page cache, frees reclaimable slab objects and pagecache.
This will cause considerable amount of thrashing of swap on an over-committed
system.

-t N, --timeout T
run each stress test for at least T seconds. One can also specify the units of time
in seconds, minutes, hours, days or years with the suffix s, m, h, d or y. Each
stressor will be sent a SIGALRM signal at the timeout time, however if the stress
test is swapped out, in an uninterruptible system call or performing clean up (such
as removing hundreds of test file) it may take a while to finally terminate. A 0
timeout will run stress-ng for ever with no timeout. The default timeout is 24
hours.

--times
show the cumulative user and system times of all the child processes at the end of
the stress run. The percentage of utilisation of available CPU time is also
calculated from the number of on-line CPUs in the system.

--timestamp
add a timestamp in hours, minutes, seconds and hundredths of a second to the log
output.

--timer-slack N
adjust the per process timer slack to N nanoseconds (Linux only). Increasing the
timer slack allows the kernel to coalesce timer events by adding some fuzziness to
timer expiration times and hence reduce wakeups. Conversely, decreasing the timer
slack will increase wakeups. A value of 0 for the timer-slack will set the system
default of 50,000 nanoseconds.

--tz collect temperatures from the available thermal zones on the machine (Linux only).
Some devices may have one or more thermal zones, where as others may have none.

-v, --verbose
show all debug, warnings and normal information output.

--verify
verify results when a test is run. This is not available on all tests. This will
sanity check the computations or memory contents from a test run and report to
stderr any unexpected failures.

--verifiable
print the names of stressors that can be verified with the --verify option.

-V, --version
show version of stress-ng, version of toolchain used to build stress-ng and system
information.

--vmstat S
every S seconds show statistics about processes, memory, paging, block I/O,
interrupts, context switches, disks and cpu activity. The output is similar that
to the output from the vmstat(8) utility. Not fully supported on various UNIX
systems.

--with list
specify stressors to run when using the --all, --seq or --permute options. For
example to run 5 instances of the cpu, hash, nop and vm stressors one after another
(sequentially) for 1 minute per stressor use:

stress-ng --seq 5 --with cpu,hash,nop,vm --timeout 1m

-x, --exclude list
specify a list of one or more stressors to exclude (that is, do not run them).
This is useful to exclude specific stressors when one selects many stressors to run
using the --class option, --sequential, --all and --random options. Example, run
the cpu class stressors concurrently and exclude the numa and search stressors:

stress-ng --class cpu --all 1 -x numa,bsearch,hsearch,lsearch

-Y, --yaml filename
output gathered statistics to a YAML formatted file named 'filename'.

Stressor specific options:

Access stressor
--access N
start N workers that work through various settings of file mode bits (read,
write, execute) for the file owner and checks if the user permissions of the
file using access(2) and faccessat(2) are sane.

--access-ops N
stop access workers after N bogo access sanity checks.

POSIX Access Control List Stressor
--acl N
start N workers that exercise permutations of ACL access permission settings
on user, group and other tags.

--acl-rand
randomize (by shuffling) the order of the ACL access permissions before
exercising ACLs.

--acl-ops N
stop acl workers after N bogo acl settings have been set.

Affinity stressor
--affinity N
start N workers that run 16 processes that rapidly change CPU affinity (only
on Linux). Rapidly switching CPU affinity can contribute to poor cache
behaviour and high context switch rate.

--affinity-delay N
delay for N nanoseconds before changing affinity to the next CPU. The delay
will spin on CPU scheduling yield operations for N nanoseconds before the
process is moved to another CPU. The default is 0 nanosconds.

--affinity-ops N
stop affinity workers after N bogo affinity operations.

--affinity-pin
pin all the 16 per stressor processes to a CPU. All 16 processes follow the
CPU chosen by the main parent stressor, forcing heavy per CPU loading.

--affinity-rand
switch CPU affinity randomly rather than the default of sequentially.

--affinity-sleep N
sleep for N nanoseconds before changing affinity to the next CPU.

Kernel crypto AF_ALG API stressor
--af-alg N
start N workers that exercise the AF_ALG socket domain by hashing and
encrypting various sized random messages. This exercises the available hashes,
ciphers, rng and aead crypto engines in the Linux kernel.

--af-alg-dump
dump the internal list representing cryptographic algorithms parsed from the
/proc/crypto file to standard output (stdout).

--af-alg-ops N
stop af-alg workers after N AF_ALG messages are hashed.

Asynchronous I/O stressor (POSIX AIO)
--aio N
start N workers that issue multiple small asynchronous I/O writes and reads on
a relatively small temporary file using the POSIX aio interface. This will
just hit the file system cache and soak up a lot of user and kernel time in
issuing and handling I/O requests. By default, each worker process will
handle 16 concurrent I/O requests.

--aio-ops N
stop POSIX asynchronous I/O workers after N bogo asynchronous I/O requests.

--aio-requests N
specify the number of POSIX asynchronous I/O requests each worker should
issue, the default is 16; 1 to 4096 are allowed.

Asynchronous I/O stressor (Linux AIO)
--aiol N
start N workers that issue multiple 4K random asynchronous I/O writes using
the Linux aio system calls io_setup(2), io_submit(2), io_getevents(2) and
io_destroy(2). By default, each worker process will handle 16 concurrent I/O
requests.

--aiol-ops N
stop Linux asynchronous I/O workers after N bogo asynchronous I/O requests.

--aiol-requests N
specify the number of Linux asynchronous I/O requests each worker should
issue, the default is 16; 1 to 4096 are allowed.

Alarm stressor
--alarm N
start N workers that exercise alarm(2) with MAXINT, 0 and random alarm and
sleep delays that get prematurely interrupted. Before each alarm is scheduled
any previous pending alarms are cancelled with zero second alarm calls.

--alarm-ops N
stop after N alarm bogo operations.

AppArmor stressor
--apparmor N
start N workers that exercise various parts of the AppArmor interface.
Currently one needs root permission to run this particular test. Only
available on Linux systems with AppArmor support and requires the
CAP_MAC_ADMIN capability.

--apparmor-ops
stop the AppArmor workers after N bogo operations.

Atomic stressor
--atomic N
start N workers that exercise various GCC __atomic_*() built in operations on
8, 16, 32 and 64 bit integers that are shared among the N workers. This
stressor is only available for builds using GCC 4.7.4 or higher. The stressor
forces many front end cache stalls and cache references.

--atomic-ops N
stop the atomic workers after N bogo atomic operations.

Bad alternative stack stressor
--bad-altstack N
start N workers that create broken alternative signal stacks for SIGSEGV and
SIGBUS handling that in turn create secondary SIGSEGV/SIGBUS errors. A
variety of randonly selected nefarious methods are used to create the stacks:

• Unmapping the alternative signal stack, before triggering the signal
handling.
• Changing the alternative signal stack to just being read only, write only,
execute only.
• Using a NULL alternative signal stack.
• Using the signal handler object as the alternative signal stack.
• Unmapping the alternative signal stack during execution of the signal
handler.
• Using a read-only text segment for the alternative signal stack.
• Using an undersized alternative signal stack.
• Using the VDSO as an alternative signal stack.
• Using an alternative stack mapped onto /dev/zero.
• Using an alternative stack mapped to a zero sized temporary file to generate
a SIGBUS error.

--bad-altstack-ops N
stop the bad alternative stack stressors after N SIGSEGV bogo operations.

Bad ioctl stressor
--bad-ioctl N
start N workers that perform a range of illegal bad read ioctls (using _IOR)
across the device drivers. This exercises page size, 64 bit, 32 bit, 16 bit
and 8 bit reads as well as NULL addresses, non-readable pages and PROT_NONE
mapped pages. Currently only for Linux and requires the --pathological option.

--bad-ioctl-method [ inc | random | random-inc | stride ]
select the method of changing the ioctl command (number, type) tuple per
iteration, the default is random-inc. Available bad-ioctl methods are
described as follows:

Method Description
inc increment ioctl command by 1
random use a random ioctl command
random-inc increment ioctl command by a random value
random-stride increment ioctl command number by 1 and decrement command type
by 3

--bad-ioctl-ops N
stop the bad ioctl stressors after N bogo ioctl operations.

Big heap stressor
-B N, --bigheap N
start N workers that grow their heaps by reallocating memory. If the out of
memory killer (OOM) on Linux kills the worker or the allocation fails then the
allocating process starts all over again. Note that the OOM adjustment for
the worker is set so that the OOM killer will treat these workers as the first
candidate processes to kill.

--bigheap-bytes N
maximum heap growth as N bytes per bigheap worker. One can specify the size as
% of total available memory or in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g.

--bigheap-growth N
specify amount of memory to grow heap by per iteration. Size can be from 4K to
64MB. Default is 64K.

--bigheap-mlock
attempt to mlock future allocated pages into memory causing more memory
pressure. If mlock(MCL_FUTURE) is implemented then this will stop newly
allocated pages from being swapped out.

--bigheap-ops N
stop the big heap workers after N bogo allocation operations are completed.

Binderfs stressor
--binderfs N
start N workers that mount, exercise and unmount binderfs. The binder control
device is exercised with 256 sequential BINDER_CTL_ADD ioctl calls per loop.

--binderfs-ops N
stop after N binderfs cycles.

Bind mount stressor
--bind-mount N
start N workers that repeatedly bind mount / to / inside a user namespace.
This can consume resources rapidly, forcing out of memory situations. Do not
use this stressor unless you want to risk hanging your machine.

--bind-mount-ops N
stop after N bind mount bogo operations.

Bitonic sort stressor
--bitonicsort N
start N workers that sort 32 bit integers using bitonic sort.

--bitonicsort-ops N
stop bitonic sort stress workers after N bogo bitonic sorts.

--bitonicsort-size N
specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

Branch stressor
--branch N
start N workers that randomly branch to 1024 randomly selected locations and
hence exercise the CPU branch prediction logic.

--branch-ops N
stop the branch stressors after N × 1024 branches

Brk stressor
--brk N
start N workers that grow the data segment by one page at a time using
multiple brk(2) calls. Each successfully allocated new page is touched to
ensure it is resident in memory. If an out of memory condition occurs then
the test will reset the data segment to the point before it started and repeat
the data segment resizing over again. The process adjusts the out of memory
setting so that it may be killed by the out of memory (OOM) killer before
other processes. If it is killed by the OOM killer then it will be
automatically re-started by a monitoring parent process.

--brk-bytes N
maximum brk growth as N bytes per brk worker. One can specify the size as % of
total available memory or in units of Bytes, KBytes, MBytes and GBytes using
the suffix b, k, m or g.

--brk-mlock
attempt to mlock future brk pages into memory causing more memory pressure. If
mlock(MCL_FUTURE) is implemented then this will stop new brk pages from being
swapped out.

--brk-notouch
do not touch each newly allocated data segment page. This disables the default
of touching each newly allocated page and hence avoids the kernel from
necessarily backing the page with physical memory.

--brk-ops N
stop the brk workers after N bogo brk operations.

Binary search stressor
--bsearch N
start N workers that binary search a sorted array of 32 bit integers using
bsearch(3). By default, there are 65536 elements in the array. This is a
useful method to exercise random access of memory and processor cache.

--bsearch-method [ bsearch-libc | bsearch-nonlibc ]
select either the libc implementation of bsearch or a slightly optimized non-
libc implementation of bsearch. The default is the libc implementation if it
exists, otherwise the non-libc version.

--bsearch-ops N
stop the bsearch worker after N bogo bsearch operations are completed.

--bsearch-size N
specify the size (number of 32 bit integers) in the array to bsearch. Size can
be from 1K to 4M.

Cache stressor
-C N, --cache N
start N workers that perform random wide spread memory read and writes to
thrash the CPU cache. The code does not intelligently determine the CPU cache
configuration and so it may be sub-optimal in producing hit-miss read/write
activity for some processors. Note: to exercise cache misses it is
recommended to instead use the matrix-3d stessor using the --matrix-3d-zyx
option.

--cache-cldemote
cache line demote (x86 only). This is a no-op for non-x86 architectures and
older x86 processors that do not support this feature.

--cache-clflushopt
use optimized cache line flush (x86 only). This is a no-op for non-x86
architectures and older x86 processors that do not support this feature.

--cache-clwb
cache line writeback (x86 only). This is a no-op for non-x86 architectures and
older x86 processors that do not support this feature.

--cache-enable-all
where appropriate exercise the cache using cldemote, clflushopt, fence, flush,
sfence and prefetch.

--cache-fence
force write serialization on each store operation (x86 only). This is a no-op
for non-x86 architectures.

--cache-flush
force flush cache on each store operation (x86 only). This is a no-op for non-
x86 architectures.

--cache-level N
specify level of cache to exercise (1=L1 cache, 2=L2 cache, 3=L3/LLC cache
(the default)). If the cache hierarchy cannot be determined, built-in
defaults will apply.

--cache-no-affinity
do not change processor affinity when --cache is in effect.

--cache-ops N
stop cache thrash workers after N bogo cache thrash operations.

--cache-prefetch
force read prefetch on next read address on architectures that support
prefetching.

--cache-sfence
force write serialization on each store operation using the sfence instruction
(x86 only). This is a no-op for non-x86 architectures.

--cache-size N
override the default cache size setting to N bytes. One can specify the in
units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--cache-ways N
specify the number of cache ways to exercise. This allows a subset of the
overall cache size to be exercised.

Cache line stressor
--cacheline N
start N workers that exercise reading and writing individual bytes in a shared
buffer that is the size of a cache line. Each stressor has 2 running processes
that exercise just two bytes that are next to each other. The intent is to
try and trigger cacheline corruption, stalls and misses with shared memory
accesses. For an N byte sized cacheline, it is recommended to run N / 2
stressor instances.

--cacheline-affinity
frequently change CPU affinity, spread cacheline processes evenly across all
online CPUs to try and maximize lower-level cache activity. Attempts to keep
adjacent cachelines being exercised by adjacent CPUs.

--cacheline-method method
specify a cacheline stress method. By default, all the stress methods are
exercised sequentially, however one can specify just one method to be used if
required. Available cacheline stress methods are described as follows:

Method Description
all iterate over all the below cpu stress methods.
adjacent increment a specific byte in a cacheline and read the adjacent
byte, check for corruption every 7 increments.
atomicinc atomically increment a specific byte in a cacheline and check for
corruption every 7 increments.
bits write and read back shifted bit patterns into specific byte in a
cacheline and check for corruption.
copy copy an adjacent byte to a specific byte in a cacheline.
inc increment and read back a specific byte in a cacheline and check
for corruption every 7 increments.
mix perform a mix of increment, left and right rotates a specific byte
in a cacheline and check for corruption.
rdfwd64 increment a specific byte in a cacheline and then read in forward
direction an entire cacheline using 64 bit reads.
rdints increment a specific byte in a cacheline and then read data at that
byte location in naturally aligned locations integer values of size
8, 16, 32, 64 and 128 bits.
rdrev64 increment a specific byte in a cacheline and then read in reverse
direction an entire cacheline using 64 bit reads.
rdwr read and write the same 8 bit value into a specific byte in a
cacheline and check for corruption.

--cacheline-ops N
stop cacheline workers after N loops of the byte exercising in a cacheline.

Process capabilities stressor
--cap N
start N workers that read per process capabilities via calls to capget(2)
(Linux only).

--cap-ops N
stop after N cap bogo operations.

Cgroup stressor
--cgroup N
start N workers that mount a cgroup, move a child to the cgroup, read, write
and remove the child from the cgroup and umount the cgroup per bogo-op
iteration. This uses cgroup v2 and is only available for Linux systems.

--cgroup-ops N
stop after N cgroup bogo operations.

Chattr stressor
--chattr N
start N workers that attempt to exercise file attributes via the
EXT2_IOC_SETFLAGS ioctl. This is intended to be intentionally racy and
exercise a range of chattr attributes by enabling and disabling them on a file
shared amongst the N chattr stressor processes. (Linux only).

--chattr-ops N
stop after N chattr bogo operations.

Chdir stressor
--chdir N
start N workers that change directory between directories using chdir(2).

--chdir-dirs N
exercise chdir on N directories. The default is 8192 directories, this allows
64 to 65536 directories to be used instead.

--chdir-ops N
stop after N chdir bogo operations.

Chmod stressor
--chmod N
start N workers that change the file mode bits via chmod(2) and fchmod(2) on
the same file. The greater the value for N then the more contention on the
single file. The stressor will work through all the combination of mode bits.

--chmod-ops N
stop after N chmod bogo operations.

Chown stressor
--chown N
start N workers that exercise chown(2) on the same file. The greater the value
for N then the more contention on the single file.

--chown-ops N
stop the chown workers after N bogo chown(2) operations.

Chroot stressor
--chroot N
start N workers that exercise chroot(2) on various valid and invalid chroot
paths. Only available on Linux systems and requires the CAP_SYS_ADMIN
capability.

--chroot-ops N
stop the chroot workers after N bogo chroot(2) operations.

Clock stressor
--clock N
start N workers exercising clocks and POSIX timers. For all known clock types
this will exercise clock_getres(2), clock_gettime(2) and clock_nanosleep(2).
For all known timers it will create a random duration timer and busy poll this
until it expires. This stressor will cause frequent context switching.

--clock-ops N
stop clock stress workers after N bogo operations.

Clone stressor
--clone N
start N workers that create clones (via the clone(2) and clone3() system
calls). This will rapidly try to create a default of 8192 clones that
immediately die and wait in a zombie state until they are reaped. Once the
maximum number of clones is reached (or clone fails because one has reached
the maximum allowed) the oldest clone thread is reaped and a new clone is then
created in a first-in first-out manner, and then repeated. A random clone
flag is selected for each clone to try to exercise different clone operations.
The clone stressor is a Linux only option.

--clone-max N
try to create as many as N clone threads. This may not be reached if the
system limit is less than N.

--clone-ops N
stop clone stress workers after N bogo clone operations.

Close stressor
--close N
start N workers that try to force race conditions on closing opened file
descriptors. These file descriptors have been opened in various ways to try
and exercise different kernel close handlers.

--close-ops N
stop close workers after N bogo close operations.

Swapcontext stressor
--context N
start N workers that run three threads that use swapcontext(3) to implement
the thread-to-thread context switching. This exercises rapid process context
saving and restoring and is bandwidth limited by register and memory save and
restore rates.

--context-ops N
stop context workers after N bogo context switches. In this stressor, 1 bogo
op is equivalent to 1000 swapcontext calls.

Copy file stressor
--copy-file N
start N stressors that copy a file using the Linux copy_file_range(2) system
call. 128 KB chunks of data are copied from random locations from one file to
random locations to a destination file. By default, the files are 256 MB in
size. Data is sync'd to the filesystem after each copy_file_range(2) call.

--copy-file-bytes N
copy file size, the default is 256 MB. One can specify the size as % of free
space on the file system or in units of Bytes, KBytes, MBytes and GBytes using
the suffix b, k, m or g.

--copy-file-ops N
stop after N copy_file_range() calls.

CPU stressor
-c N, --cpu N
start N workers exercising the CPU by sequentially working through all the
different CPU stress methods. Instead of exercising all the CPU stress
methods, one can specify a specific CPU stress method with the --cpu-method
option.

-l P, --cpu-load P
load CPU with P percent loading for the CPU stress workers. 0 is effectively a
sleep (no load) and 100 is full loading. The loading loop is broken into
compute time (load%) and sleep time (100% - load%). Accuracy depends on the
overall load of the processor and the responsiveness of the scheduler, so the
actual load may be different from the desired load. Note that the number of
bogo CPU operations may not be linearly scaled with the load as some systems
employ CPU frequency scaling and so heavier loads produce an increased CPU
frequency and greater CPU bogo operations.

Note: This option only applies to the --cpu stressor option and not to all of
the cpu class of stressors.

--cpu-load-slice S
note - this option is only useful when --cpu-load is less than 100%. The CPU
load is broken into multiple busy and idle cycles. Use this option to specify
the duration of a busy time slice. A negative value for S specifies the
number of iterations to run before idling the CPU (e.g. -30 invokes 30
iterations of a CPU stress loop). A zero value selects a random busy time
between 0 and 0.5 seconds. A positive value for S specifies the number of
milliseconds to run before idling the CPU (e.g. 100 keeps the CPU busy for 0.1
seconds). Specifying small values for S lends to small time slices and
smoother scheduling. Setting --cpu-load as a relatively low value and
--cpu-load-slice to be large will cycle the CPU between long idle and busy
cycles and exercise different CPU frequencies. The thermal range of the CPU
is also cycled, so this is a good mechanism to exercise the scheduler,
frequency scaling and passive/active thermal cooling mechanisms.

Note: This option only applies to the --cpu stressor option and not to all of
the cpu class of stressors.

--cpu-method method
specify a cpu stress method. By default, all the stress methods are exercised
sequentially, however one can specify just one method to be used if required.
Available cpu stress methods are described as follows:

Method Description
all iterate over all the below cpu stress methods
ackermann Ackermann function: compute A(3, 7), where:
A(m, n) = n + 1 if m = 0;
A(m - 1, 1) if m > 0 and n = 0;
A(m - 1, A(m, n - 1)) if m > 0 and n > 0
apery calculate Apery's constant ζ(3); the sum of 1/(n ↑ 3) to a
precision of 1.0x10↑14
bitops various bit operations from bithack, namely: reverse bits,
parity check, bit count, round to nearest power of 2
callfunc recursively call 8 argument C function to a depth of 1024
calls and unwind
cfloat 1000 iterations of a mix of floating point complex
operations
cdouble 1000 iterations of a mix of double floating point complex
operations
clongdouble 1000 iterations of a mix of long double floating point
complex operations

collatz compute the 1348 steps in the collatz sequence starting from
number 989345275647. Where f(n) = n / 2 (for even n) and
f(n) = 3n + 1 (for odd n).
correlate perform a 8192 × 512 correlation of random doubles
crc16 compute 1024 rounds of CCITT CRC16 on random data
decimal32 1000 iterations of a mix of 32 bit decimal floating point
operations (GCC only)
decimal64 1000 iterations of a mix of 64 bit decimal floating point
operations (GCC only)
decimal128 1000 iterations of a mix of 128 bit decimal floating point
operations (GCC only)
dither Floyd-Steinberg dithering of a 1024 × 768 random image from
8 bits down to 1 bit of depth
div8 50,000 8 bit unsigned integer divisions
div16 50,000 16 bit unsigned integer divisions
div32 50,000 32 bit unsigned integer divisions
div64 50,000 64 bit unsigned integer divisions
div128 50,000 128 bit unsigned integer divisions
double 1000 iterations of a mix of double precision floating point
operations
euler compute e using n = (1 + (1 ÷ n)) ↑ n
explog iterate on n = exp(log(n) ÷ 1.00002)
factorial find factorials from 1..150 using Stirling's and Ramanujan's
approximations
fibonacci compute Fibonacci sequence of 0, 1, 1, 2, 5, 8...
fft 4096 sample Fast Fourier Transform
fletcher16 1024 rounds of a naïve implementation of a 16 bit Fletcher's
checksum
float 1000 iterations of a mix of floating point operations
float16 1000 iterations of a mix of 16 bit floating point operations
float32 1000 iterations of a mix of 32 bit floating point operations
float64 1000 iterations of a mix of 64 bit floating point operations
float80 1000 iterations of a mix of 80 bit floating point operations
float128 1000 iterations of a mix of 128 bit floating point
operations
floatconversion perform 65536 iterations of floating point conversions
between float, double and long double floating point
variables.
gamma calculate the Euler-Mascheroni constant γ using the limiting
difference between the harmonic series (1 + 1/2 + 1/3 + 1/4
+ 1/5 ... + 1/n) and the natural logarithm ln(n), for n =
80000.
gcd compute GCD of integers
gray calculate binary to gray code and gray code back to binary
for integers from 0 to 65535
hamming compute Hamming H(8,4) codes on 262144 lots of 4 bit data.
This turns 4 bit data into 8 bit Hamming code containing 4
parity bits. For data bits d1..d4, parity bits are computed
as:
p1 = d2 + d3 + d4
p2 = d1 + d3 + d4
p3 = d1 + d2 + d4
p4 = d1 + d2 + d3
hanoi solve a 21 disc Towers of Hanoi stack using the recursive
solution
hyperbolic compute sinh(θ) × cosh(θ) + sinh(2θ) + cosh(3θ) for float,
double and long double hyperbolic sine and cosine functions
where θ = 0 to 2π in 1500 steps
idct 8 × 8 IDCT (Inverse Discrete Cosine Transform).
int8 1000 iterations of a mix of 8 bit integer operations.
int16 1000 iterations of a mix of 16 bit integer operations.
int32 1000 iterations of a mix of 32 bit integer operations.
int64 1000 iterations of a mix of 64 bit integer operations.
int128 1000 iterations of a mix of 128 bit integer operations (GCC
only).
int32float 1000 iterations of a mix of 32 bit integer and floating
point operations.
int32double 1000 iterations of a mix of 32 bit integer and double
precision floating point operations.
int32longdouble 1000 iterations of a mix of 32 bit integer and long double
precision floating point operations.
int64float 1000 iterations of a mix of 64 bit integer and floating
point operations.

int64double 1000 iterations of a mix of 64 bit integer and double
precision floating point operations.
int64longdouble 1000 iterations of a mix of 64 bit integer and long double
precision floating point operations.
int128float 1000 iterations of a mix of 128 bit integer and floating
point operations (GCC only).
int128double 1000 iterations of a mix of 128 bit integer and double
precision floating point operations (GCC only).
int128longdouble 1000 iterations of a mix of 128 bit integer and long double
precision floating point operations (GCC only).
int128decimal32 1000 iterations of a mix of 128 bit integer and 32 bit
decimal floating point operations (GCC only).
int128decimal64 1000 iterations of a mix of 128 bit integer and 64 bit
decimal floating point operations (GCC only).
int128decimal128 1000 iterations of a mix of 128 bit integer and 128 bit
decimal floating point operations (GCC only).
intconversion perform 65536 iterations of integer conversions between
int16, int32 and int64 variables.
ipv4checksum compute 1024 rounds of the 16 bit ones' complement IPv4
checksum.
jmp Simple unoptimised compare >, <, == and jmp branching.
lfsr32 16384 iterations of a 32 bit Galois linear feedback shift
register using the polynomial x↑32 + x↑31 + x↑29 + x + 1.
This generates a ring of 2↑32 - 1 unique values (all 32 bit
values except for 0).
ln2 compute ln(2) based on series:
1 - 1/2 + 1/3 - 1/4 + 1/5 - 1/6 ...
logmap 16384 iterations computing chaotic double precision values
using the logistic map Χn+1 = r × Χn × (1 - Χn) where r > ≈
3.56994567
longdouble 1000 iterations of a mix of long double precision floating
point operations.
loop simple empty loop.
matrixprod matrix product of two 128 × 128 matrices of double floats.
Testing on 64 bit x86 hardware shows that this is provides a
good mix of memory, cache and floating point operations and
is probably the best CPU method to use to make a CPU run
hot.
nsqrt compute sqrt() of long doubles using Newton-Raphson.
omega compute the omega constant defined by Ωe↑Ω = 1 using
efficient iteration of Ωn+1 = (1 + Ωn) / (1 + e↑Ωn).
parity compute parity using various methods from the Standford Bit
Twiddling Hacks. Methods employed are: the naïve way, the
naïve way with the Brian Kernigan bit counting optimisation,
the multiply way, the parallel way, the lookup table ways (2
variations) and using the __builtin_parity function.
phi compute the Golden Ratio ϕ using series.
pi compute π using the Srinivasa Ramanujan fast convergence
algorithm.
prime find the first 10000 prime numbers using a slightly
optimised brute force naïve trial division search.
psi compute ψ (the reciprocal Fibonacci constant) using the sum
of the reciprocals of the Fibonacci numbers.
queens compute all the solutions of the classic 8 queens problem
for board sizes 1..11.
rand 16384 iterations of rand(), where rand is the MWC pseudo
random number generator. The MWC random function
concatenates two 16 bit multiply-with-carry generators:
x(n) = 36969 × x(n - 1) + carry,
y(n) = 18000 × y(n - 1) + carry mod 2 ↑ 16

and has period of around 2 ↑ 60.
rand48 16384 iterations of drand48(3) and lrand48(3).
rgb convert RGB to YUV and back to RGB (CCIR 601).
sieve find the first 10000 prime numbers using the sieve of
Eratosthenes.
stats calculate minimum, maximum, arithmetic mean, geometric mean,
harmoninc mean and standard deviation on 250 randomly
generated positive double precision values.
sqrt compute sqrt(rand()), where rand is the MWC pseudo random
number generator.

trig compute sin(θ) × cos(θ) + sin(2θ) + cos(3θ) for float,
double and long double sine and cosine functions where θ = 0
to 2π in 1500 steps.
union perform integer arithmetic on a mix of bit fields in a C
union. This exercises how well the compiler and CPU can
perform integer bit field loads and stores.
zeta compute the Riemann Zeta function ζ(s) for s = 2.0..10.0

Note that some of these methods try to exercise the CPU with computations
found in some real world use cases. However, the code has not been optimised
on a per-architecture basis, so may be a sub-optimal compared to hand-
optimised code used in some applications. They do try to represent the
typical instruction mixes found in these use cases.

--cpu-old-metrics
as of version V0.14.02 the cpu stressor now normalizes each of the cpu
stressor method bogo-op counters to try and ensure a similar bogo-op rate for
all the methods to avoid the shorter running (and faster) methods from skewing
the bogo-op rates when using the default "all" method. This is based on a
reference Intel i5-8350U processor and hence the bogo-ops normalizing factors
will be skew somewhat on different CPUs, but so significantly as the original
bogo-op counter rates. To disable the normalization and fall back to the
original metrics, use this option.

--cpu-ops N
stop cpu stress workers after N bogo operations.

CPU onlining stressor
--cpu-online N
start N workers that put randomly selected CPUs offline and online. This Linux
only stressor requires root privilege to perform this action. By default the
first CPU (CPU 0) is never offlined as this has been found to be problematic
on some systems and can result in a shutdown.

--cpu-online-affinity
move the stressor worker to the CPU that will be next offlined.

--cpu-online-all
The default is to never offline the first CPU. This option will offline and
online all the CPUs including CPU 0. This may cause some systems to shutdown.

--cpu-online-ops N
stop after offline/online operations.

Crypt stressor
--crypt N
start N workers that encrypt a 16 character random password using crypt(3).
The password is encrypted using MD5, NT, SHA-1, SHA-256, SHA-512, scrypt,
SunMD5 and yescrypt encryption methods.

--crypt-method method
select the encryption method, may be one of: all, MD5, NT, SHA-1, SHA-256,
SHA-512, scrypt, SunMD5 or yescrypt. The 'all' method selects all the methods
and is the default.

--crypt-ops N
stop after N bogo encryption operations.

Cyclic stressor
--cyclic N
start N workers that exercise the real time FIFO or Round Robin schedulers
with cyclic nanosecond sleeps. Normally one would just use 1 worker instance
with this stressor to get reliable statistics. By default this stressor
measures the first 10 thousand latencies and calculates the mean, mode,
minimum, maximum latencies along with various latency percentiles for the just
the first cyclic stressor instance. One has to run this stressor with
CAP_SYS_NICE capability to enable the real time scheduling policies. The FIFO
scheduling policy is the default.

--cyclic-dist N
calculate and print a latency distribution with the interval of N nanoseconds.
This is helpful to see where the latencies are clustering.

Method Description
clock_ns sleep for the specified time using the clock_nanosleep(2) high
resolution nanosleep and the CLOCK_REALTIME real time clock.
itimer wakeup a paused process with a CLOCK_REALTIME itimer signal.
poll delay for the specified time using a poll delay loop that checks for
time changes using clock_gettime(2) on the CLOCK_REALTIME clock.
posix_ns sleep for the specified time using the POSIX nanosleep(2) high
resolution nanosleep.
pselect sleep for the specified time using pselect(2) with null file
descriptors.
usleep sleep to the nearest microsecond using usleep(2).

--cyclic-ops N
stop after N sleeps.

--cyclic-policy [ fifo | rr ]
specify the desired real time scheduling policy, ff (first-in, first-out) or
rr (round-robin).

--cyclic-prio P
specify the scheduling priority P. Range from 1 (lowest) to 100 (highest).

--cyclic-samples N
measure N samples. Range from 1 to 100000000 samples.

--cyclic-sleep N
sleep for N nanoseconds per test cycle using clock_nanosleep(2) with the
CLOCK_REALTIME timer. Range from 1 to 1000000000 nanoseconds.

Daemon stressor
--daemon N
start N workers that each create a daemon that dies immediately after creating
another daemon and so on. This effectively works through the process table
with short lived processes that do not have a parent and are waited for by
init. This puts pressure on init to do rapid child reaping. The daemon
processes perform the usual mix of calls to turn into typical UNIX daemons, so
this artificially mimics very heavy daemon system stress.

--daemon-ops N
stop daemon workers after N daemons have been created.

--daemon-wait
wait for daemon child processes rather than let init handle the waiting.
Enabling this option will reduce the daemon fork rate because of the
synchronous wait delays.

Datagram congestion control protocol (DCCP) stressor
--dccp N
start N workers that send and receive data using the Datagram Congestion
Control Protocol (DCCP) (RFC4340). This involves a pair of client/server
processes performing rapid connect, send and receives and disconnects on the
local host.

--dccp-domain D
specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are
supported.

--dccp-if NAME
use network interface NAME. If the interface NAME does not exist, is not up or
does not support the domain then the loopback (lo) interface is used as the
default.

--dccp-msgs N
send N messages per connect, send/receive, disconnect iteration. The default
is 10000 messages. If N is too small then the rate is throttled back by the
overhead of dccp socket connect and disconnects.

--dccp-port P
start DCCP at port P. For N dccp worker processes, ports P to P - 1 are used.

--dccp-ops N
stop dccp stress workers after N bogo operations.

--dccp-opts [ send | sendmsg | sendmmsg ]
by default, messages are sent using send(2). This option allows one to specify
the sending method using send(2), sendmsg(2) or sendmmsg(2). Note that
sendmmsg is only available for Linux systems that support this system call.

Mutex using Dekker algorithm stressor
--dekker N
start N workers that exercises mutex exclusion between two processes using
shared memory with the Dekker Algorithm. Where possible this uses memory
fencing and falls back to using GCC __sync_synchronize if they are not
available. The stressors contain simple mutex and memory coherency sanity
checks.

--dekker-ops N
stop dekker workers after N mutex operations.

Dentry stressor
-D N, --dentry N
start N workers that create and remove directory entries. This should create
file system meta data activity. The directory entry names are suffixed by a
gray-code encoded number to try to mix up the hashing of the namespace.

--dentry-ops N
stop denty thrash workers after N bogo dentry operations.

--dentry-order [ forward | reverse | stride | random ]
specify unlink order of dentries, can be one of forward, reverse, stride or
random. By default, dentries are unlinked in random order. The forward order
will unlink them from first to last, reverse order will unlink them from last
to first, stride order will unlink them by stepping around order in a quasi-
random pattern and random order will randomly select one of forward, reverse
or stride orders.

--dentries N
create N dentries per dentry thrashing loop, default is 2048.

/dev stressor
--dev N
start N workers that exercise the /dev devices. Each worker runs 5 concurrent
threads that perform open(2), fstat(2), lseek(2), poll(2), fcntl(2), mmap(2),
munmap(2), fsync(2) and close(2) on each device. Note that watchdog devices
are not exercised.

--dev-file filename
specify the device file to exercise, for example, /dev/null. By default the
stressor will work through all the device files it can fine, however, this
option allows a single device file to be exercised.

--dev-ops N
stop dev workers after N bogo device exercising operations.

/dev/shm stressor
--dev-shm N
start N workers that fallocate large files in /dev/shm and then mmap these
into memory and touch all the pages. This exercises pages being moved to/from
the buffer cache. Linux only.

--dev-shm-ops N
stop after N bogo allocation and mmap /dev/shm operations.

Directories stressor
--dir N
start N workers that create, rename and remove directories using mkdir, rename
and rmdir.

--dir-dirs N
exercise dir on N directories. The default is 8192 directories, this allows 64
to 65536 directories to be used instead.

--dir-ops N
stop directory thrash workers after N bogo directory operations.

Deep directories stressor
--dirdeep N
start N workers that create a depth-first tree of directories to a maximum
depth as limited by PATH_MAX or ENAMETOOLONG (which ever occurs first). By
default, each level of the tree contains one directory, but this can be
increased to a maximum of 10 sub-trees using the --dirdeep-dir option. To
stress inode creation, a symlink and a hardlink to a file at the root of the
tree is created in each level.

--dirdeep-bytes N
allocated file size, the default is 0. One can specify the size as % of free
space on the file system or in units of Bytes, KBytes, MBytes and GBytes using
the suffix b, k, m or g. Used in conjunction with the --dirdeep-files option.

--dirdeep-dirs N
create N directories at each tree level. The default is just 1 but can be
increased to a maximum of 36 per level.

--dirdeep-files N
create N files at each tree level. The default is 0 with the file size
specified by the --dirdeep-bytes option.

--dirdeep-inodes N
consume up to N inodes per dirdeep stressor while creating directories and
links. The value N can be the number of inodes or a percentage of the total
available free inodes on the filesystem being used.

--dirdeep-ops N
stop directory depth workers after N bogo directory operations.

Maximum files creation in a directory stressor
--dirmany N
start N stressors that create as many files in a directory as possible and
then remove them. The file creation phase stops when an error occurs (for
example, out of inodes, too many files, quota reached, etc.) and then the
files are removed. This cycles until the run time is reached or the file
creation count bogo-ops metric is reached. This is a much faster and light
weight directory exercising stressor compared to the dentry stressor.

--dirmany-bytes N
allocated file size, the default is 0. One can specify the size as % of free
space on the file system or in units of Bytes, KBytes, MBytes and GBytes using
the suffix b, k, m or g.

--dirmany-ops N
stop dirmany stressors after N empty files have been created.

Dnotify stressor
--dnotify N
start N workers performing file system activities such as making/deleting
files/directories, renaming files, etc. to stress exercise the various dnotify
events (Linux only).

--dnotify-ops N
stop inotify stress workers after N dnotify bogo operations.

Dup stressor
--dup N
start N workers that perform dup(2) and then close(2) operations on /dev/zero.
The maximum opens at one time is system defined, so the test will run up to
this maximum, or 65536 open file descriptors, which ever comes first.

--dup-ops N
stop the dup stress workers after N bogo open operations.

Dynamic libraries loading stressor
--dynlib N
start N workers that dynamically load and unload various shared libraries.
This exercises memory mapping and dynamic code loading and symbol lookups. See
dlopen(3) for more details of this mechanism.

--dynlib-ops N
stop workers after N bogo load/unload cycles.

Eigen C++ matrix library stressor
--eigen N
start N workers that exercise the Eigen C++ matrix library for 2D matrix
addition, multiplication, determinant, inverse and transpose operations on
long double, double and float matrices. This currently is only available for
gcc/g++ builds.

--eigen-method method
select the floating point method to use, available methods are:

Method Description
all iterate over all the Eigen 2D matrix operations
add-longdouble addition of two matrices of long double floating
point values T{ add-doubleeT{ addition of two
matrices of double floating point values
add-float addition of two matrices of floating point values
determinant-longdouble determinant of matrix of long double floating point
values
determinant-double determinant of matrix of double floating point values
determinant-float determinant of matrix of floating point values
inverse-longdouble inverse of matrix of long double floating point
values
inverse-double inverse of matrix of double floating point values
inverse-float inverse of matrix of floating point values
multiply-longdouble mutiplication of two matrices of long double floating
point values
multiply-doublee mutiplication of two matrices of double floating
point values
multiply-float mutiplication of two matrices of floating point
values
transpose-longdouble transpose of matrix of long double floating point
values
transpose-double transpose of matrix of double floating point values
transpose-float transpose of matrix of floating point values

--eigen-ops N
stop after N Eigen matrix computations

--eigen-size N
specify the 2D matrix size N × N. The default is a 32 × 32 matrix.

EFI variables stressor
--efivar N
start N workers that exercise the Linux /sys/firmware/efi/efivars and
/sys/firmware/efi/vars interfaces by reading the EFI variables. This is a
Linux only stress test for platforms that support the EFI vars interface and
may require the CAP_SYS_ADMIN capability.

--efivar-ops N
stop the efivar stressors after N EFI variable read operations.

Non-functional system call (ENOSYS) stressor
--enosys N
start N workers that exercise non-functional system call numbers. This calls a
wide range of system call numbers to see if it can break a system where these
are not wired up correctly. It also keeps track of system calls that exist
(ones that don't return ENOSYS) so that it can focus on purely finding and
exercising non-functional system calls. This stressor exercises system calls
from 0 to __NR_syscalls + 1024, random system calls within constrained in the
ranges of 0 to 2↑8, 2↑16, 2↑24, 2↑32, 2↑40, 2↑48, 2↑56 and 2↑64 bits, high
system call numbers and various other bit patterns to try to get wide
coverage. To keep the environment clean, each system call being tested runs in
a child process with reduced capabilities.

--enosys-ops N
stop after N bogo enosys system call attempts

Environment variables stressor
--env N
start N workers that creates numerous large environment variables to try to
trigger out of memory conditions using setenv(3). If ENOMEM occurs then the
environment is emptied and another memory filling retry occurs. The process
is restarted if it is killed by the Out Of Memory (OOM) killer.

--env-ops N
stop after N bogo setenv/unsetenv attempts.

Epoll stressor
--epoll N
start N workers that perform various related socket stress activity using
epoll_wait(2) to monitor and handle new connections. This involves
client/server processes performing rapid connect, send/receives and
disconnects on the local host. Using epoll allows a large number of
connections to be efficiently handled, however, this can lead to the
connection table filling up and blocking further socket connections, hence
impacting on the epoll bogo op stats. For ipv4 and ipv6 domains, multiple
servers are spawned on multiple ports. The epoll stressor is for Linux only.

--epoll-domain D
specify the domain to use, the default is unix (aka local). Currently ipv4,
ipv6 and unix are supported.

--epoll-ops N
stop epoll workers after N bogo operations.

--epoll-port P
start at socket port P. For N epoll worker processes, ports P to (P * 4) - 1
are used for ipv4, ipv6 domains and ports P to P - 1 are used for the unix
domain.

--epoll-sockets N
specify the maximum number of concurrently open sockets allowed in server.
Setting a high value impacts on memory usage and may trigger out of memory
conditions.

Event file descriptor (eventfd) stressor
--eventfd N
start N parent and child worker processes that read and write 8 byte event
messages between them via the eventfd mechanism (Linux only).

--eventfd-nonblock
enable EFD_NONBLOCK to allow non-blocking on the event file descriptor. This
will cause reads and writes to return with EAGAIN rather the blocking and
hence causing a high rate of polling I/O.

--eventfd-ops N
stop eventfd workers after N bogo operations.

Exec processes stressor
--exec N
start N workers continually forking children that exec stress-ng and then exit
almost immediately. If a system has pthread support then 1 in 4 of the exec's
will be from inside a pthread to exercise exec'ing from inside a pthread
context.

--exec-fork-method [ clone | fork | rfork | spawn | vfork ]
select the process creation method using clone(2), fork(2), BSD rfork(2),
posix_spawn(3) or vfork(2). Note that vfork will only exec programs using
execve due to the constraints on the shared stack between the parent and the
child process.

--exec-max P
create P child processes that exec stress-ng and then wait for them to exit
per iteration. The default is 4096; higher values may create many temporary
zombie processes that are waiting to be reaped. One can potentially fill up
the process table using high values for --exec-max and --exec.

--exec-method [ all | execve | execveat ]
select the exec system call to use; all will perform a random choice between
execve(2) and execveat(2), execve will use execve(2) and execveat will use
execveat(2) if it is available.

--exec-no-pthread
do not use pthread_create(3).

--exec-ops N
stop exec stress workers after N bogo operations.

Exiting pthread groups stressor
--exit-group N
start N workers that create 16 pthreads and terminate the pthreads and the
controlling child process using exit_group(2). (Linux only stressor).

--exit-group-ops N
stop after N iterations of pthread creation and deletion loops.

Factorization of large integers stressor
--factor N
start N workers that factorize large integers using the GNU Multiple Precision
Arithmetic Library. Randomized values to be factorized are computed so that an
N digit value is comprised of about 0.4 × N random factors, for N > 100. The
default number of digits in the value to be factorized is 10.

--factor-digits N
select the number of digits in the values to be factorized. Range 8 to
100000000 digits, default is 10.

--factor-ops N
stop after N factorizations.

File space allocation (fallocate) stressor
-F N, --fallocate N
start N workers continually fallocating (preallocating file space) and
ftruncating (file truncating) temporary files. If the file is larger than the
free space, fallocate will produce an ENOSPC error which is ignored by this
stressor.

--fallocate-bytes N
allocated file size, the default is 1 GB. One can specify the size as % of
free space on the file system or in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g.

--fallocate-ops N
stop fallocate stress workers after N bogo fallocate operations.

Filesystem notification (fanotify) stressor
--fanotify N
start N workers performing file system activities such as creating, opening,
writing, reading and unlinking files to exercise the fanotify event monitoring
interface (Linux only). Each stressor runs a child process to generate file
events and a parent process to read file events using fanotify. Has to be run
with CAP_SYS_ADMIN capability.

--fanotify-ops N
stop fanotify stress workers after N bogo fanotify events.

CPU branching instruction cache stressor
--far-branch N
start N workers that exercise calls to tens of thousands of functions that are
relatively far from the caller. All functions are 1 op instructions that
return to the caller. The functions are placed in pages that are memory mapped
with a wide spread of fixed virtual addresses. Function calls are pre-
shuffled to create a randomized mix of addresses to call. This stresses the
instruction cache and any instruction TLBs.

--far-branch-ops N
stop after N far branch bogo-ops. One full cycle of calling all the tens of
thousands of functions equates to one bogo-op.

--far-branch-pages N
specify the number of pages to allocate for far branch functions. The number
for functions per page depends on the processor architecture, for example, x86
will have 4096 x 1 byte return instructions per 4K page, where as SPARC64 will
have only 512 x 8 byte return instructions per 4K page.

Page fault stressor
--fault N
start N workers that generates minor and major page faults.

--fault-ops N
stop the page fault workers after N bogo page fault operations.

Fcntl stressor
--fcntl N
start N workers that perform fcntl(2) calls with various commands. The
exercised commands (if available) are: F_DUPFD, F_DUPFD_CLOEXEC, F_GETFD,
F_SETFD, F_GETFL, F_SETFL, F_GETOWN, F_SETOWN, F_GETOWN_EX, F_SETOWN_EX,
F_GETSIG, F_SETSIG, F_GETLK, F_SETLK, F_SETLKW, F_OFD_GETLK, F_OFD_SETLK and
F_OFD_SETLKW.

--fcntl-ops N
stop the fcntl workers after N bogo fcntl operations.

File descriptor duplication and closing stressor
--fd-fork N
start N workers that open files using dup(2) on a file (/dev/zero by default)
and then copies these using multiple fork'd child processes and closes them
with the fast clone_range(2) or close(2) or by directly ending the processes
using _exit(2). For every bogo-op, the stressor attempts to dup(2) another
10000 file descriptors up to the maximum allowed, fork 8 child processes that
then close their copies of the file descriptors.

--fd-fork-fds N
specify maximum number of file descriptors to be opened. The default is 2
million, with a range of 1000 to 16 million. The actual number used may be
less depending on the system defined limits of the number of open files per
process.

--fd-fork-file [ null, random, stdin, stdout, zero ]
specify file to dup: null for /dev/null, random for /dev/random, stdin for
standard input, stdout for standard output, zero for /dev/zero. Default is
/dev/zero.

--fd-fork-ops N
stop after N rounds of 10000 dups, forking/closing/exiting and waiting for the
child processes. Note that the bogo-ops metric rate will slow down over time
as this stressor increases the number of open files per bogo-loop and this
increases the fork and close run times.

File extent (fiemap) stressor
--fiemap N
start N workers that each create a file with many randomly changing extents
and has 4 child processes per worker that gather the extent information using
the FS_IOC_FIEMAP ioctl(2).

--fiemap-bytes N
specify the size of the fiemap'd file in bytes. One can specify the size as %
of free space on the file system or in units of Bytes, KBytes, MBytes and
GBytes using the suffix b, k, m or g. Larger files will contain more extents,
causing more stress when gathering extent information.

--fiemap-ops N
stop after N fiemap bogo operations.

FIFO named pipe stressor
--fifo N
start N workers that exercise a named pipe by transmitting 64 bit integers.

--fifo-data-size N
set the byte size of the fifo write/reads, default is 8, range 8..4096.

--fifo-ops N
stop fifo workers after N bogo pipe write operations.

--fifo-readers N
for each worker, create N fifo reader workers that read the named pipe using
simple blocking reads. Default is 4, range 1..64.

File I/O control (ioctl) stressor
--file-ioctl N
start N workers that exercise various file specific ioctl(2) calls. This will
attempt to use the FIONBIO, FIOQSIZE, FIGETBSZ, FIOCLEX, FIONCLEX, FIONBIO,
FIOASYNC, FIOQSIZE, FIFREEZE, FITHAW, FICLONE, FICLONERANGE, FIONREAD,
FIONWRITE and FS_IOC_RESVSP ioctls if these are defined.

--file-ioctl-ops N
stop file-ioctl workers after N file ioctl bogo operations.

Filename stressor
--filename N
start N workers that exercise file creation using various length filenames
containing a range of allowed filename characters. This will try to see if it
can exceed the file system allowed filename length was well as test various
filename lengths between 1 and the maximum allowed by the file system.

--filename-ops N
stop filename workers after N bogo filename tests.

--filename-opts opt
use characters in the filename based on option 'opt'. Valid options are:

Option Description
probe default option, probe the file system for valid allowed characters in
a file name and use these
posix use characters as specified by The Open Group Base Specifications
Issue 7, POSIX.1-2008, 3.278 Portable Filename Character Set
ext use characters allowed by the ext2, ext3, ext4 file systems, namely
any 8 bit character apart from NUL and /

File locking (flock) stressor
--flock N
start N workers locking on a single file.

--flock-ops N
stop flock stress workers after N bogo flock operations.

Cache flushing stressor
--flush-cache N
start N workers that flush the data and instruction cache (where possible).
Some architectures may not support cache flushing on either cache, in which
case these become no-ops.

--flush-cache-ops N
stop after N cache flush iterations.

Fused Multiply/Add floating point operations (fma) stressor
--fma N
start N workers that exercise single and double precision floating point
multiplication and add operations on arrays of 512 floating point values.
More modern processors (Intel Haswell, AMD Bulldozer and Piledriver) and
modern C compilers these will be performed by fused-multiply-add (fma3)
opcodes. Operations used are:

a = a × b + c
a = b × a + c
a = b × c + a

--fma-ops N
stop after N bogo-loops of the 3 above operations on 512 single and double
precision floating point numbers.

Process forking stressor
-f N, --fork N
start N workers continually forking children that immediately exit.

--fork-max P
create P child processes and then wait for them to exit per iteration. The
default is just 1; higher values will create many temporary zombie processes
that are waiting to be reaped. One can potentially fill up the process table
using high values for --fork-max and --fork.

--fork-ops N
stop fork stress workers after N bogo operations.

--fork-unmap
attempt to unmap unused non-memory resident shared library pages to try and
reduced anonymous vma copying. This is an ugly hack for benchmarking reduced
vma copying and not guaranteed to work. Linux only.

--fork-vm
enable detrimental performance virtual memory advice using madvise on all
pages of the forked process. Where possible this will try to set every page in
the new process with using madvise MADV_MERGEABLE, MADV_WILLNEED,
MADV_HUGEPAGE and MADV_RANDOM flags. Linux only.

Heavy process forking stressor
--forkheavy N
start N workers that fork child processes from a parent that has thousands of
allocated system resources. The fork becomes a heavyweight operations as it
has to duplicate the resource references of the parent. Each stressor instance
creates and reaps up to 4096 child processes that are created and reaped in a
first-in first-out manner.

--forkheavy-allocs N
attempt N resource allocation loops per stressor instance. Resources include
pipes, file descriptors, memory mappings, pthreads, timers, ptys, semaphores,
message queues and temporary files. These create heavyweight processes that
are more time expensive to fork from. Default is 16384.

--forkheavy-mlock
attempt to mlock future allocated pages into memory causing more memory
pressure. If mlock(MCL_FUTURE) is implemented then this will stop new brk
pages from being swapped out.

--forkheavy-ops N
stop after N fork calls.

--forkheavy-procs N
attempt to fork N processes per stressor. The default is 4096 processes.

Floating point operations stressor
--fp N start N workers that exercise addition, multiplication and division operations
on a range of floating point types. For each type, 8 floating point values are
operated upon 65536 times in a loop per bogo op.

--fp-method method
select the floating point method to use, available methods are:

Method Description
all iterate over all the following floating point methods:
float128add 128 bit floating point add
float80add 80 bit floating point add
float64add 64 bit floating point add
float32add 32 bit binary32 floating point add
floatadd floating point add
doubleadd double precision floating point add
ldoubleadd long double precision floating point add
float128mul 128 bit floating point multiply
float80mul 80 bit floating point multiply
float64mul 64 bit floating point multiply
float32mul 32 bit binary32 floating point multiply
floatmul floating point multiply
doublemul double precision floating point multiply
ldoublemul long double precision floating point multiply
float128div 128 bit floating point divide
float80div 80 bit floating point divide
float64div 64 bit floating point divide
float32div 32 bit binary32 floating point divide
floatdiv floating point divide
doublediv double precision floating point divide
ldoublediv long double precision floating point divide

Note that some of these floating point methods may not be available on some
systems.

--fp-ops N
stop after N floating point bogo ops. Note that bogo-ops are counted for just
standard float, double and long double floating point types.

Floating point exception stressor
--fp-error N
start N workers that generate floating point exceptions. Computations are
performed to force and check for the FE_DIVBYZERO, FE_INEXACT, FE_INVALID,
FE_OVERFLOW and FE_UNDERFLOW exceptions. EDOM and ERANGE errors are also
checked.

--fp-error-ops N
stop after N bogo floating point exceptions.

File punch and hole filling stressor
--fpunch N
start N workers that punch and fill holes in a 16 MB file using five
concurrent processes per stressor exercising on the same file. Where
available, this uses fallocate(2) FALLOC_FL_KEEP_SIZE, FALLOC_FL_PUNCH_HOLE,
FALLOC_FL_ZERO_RANGE, FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE to
make and fill holes across the file and breaks it into multiple extents.

--fpunch-bytes N
set maximum size of each file for each fpunch worker process, the default is
16 MB. One can specify the size as % of free space on the file system or in
units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--fpunch-ops N
stop fpunch workers after N punch and fill bogo operations.

File size limit stressor
--fsize N
start N workers that exercise file size limits (via setrlimit RLIMIT_FSIZE)
with file sizes that are fixed, random and powers of 2. The files are
truncated and allocated to trigger SIGXFSZ signals.

--fsize-ops N
stop after N bogo file size test iterations.

File stats (fstat) stressor
--fstat N
start N workers fstat'ing files in a directory (default is /dev).

--fstat-dir directory
specify the directory to fstat to override the default of /dev. All the files
in the directory will be fstat'd repeatedly.

--fstat-ops N
stop fstat stress workers after N bogo fstat operations.

/dev/full stressor
--full N
start N workers that exercise /dev/full. This attempts to write to the device
(which should always get error ENOSPC), to read from the device (which should
always return a buffer of zeros) and to seek randomly on the device (which
should always succeed). (Linux only).

--full-ops N
stop the stress full workers after N bogo I/O operations.

Function argument passing stressor
--funccall N
start N workers that call functions of 1 through to 9 arguments. By default
all functions with a range of argument types are called, however, this can be
changed using the --funccall-method option. This exercises stack function
argument passing and re-ordering on the stack and in registers.

--funccall-ops N
stop the funccall workers after N bogo function call operations. Each bogo
operation is 1000 calls of functions of 1 through to 9 arguments of the chosen
argument type.

--funccall-method method
specify the method of funccall argument type to be used. The default is all
the types but can be one of bool, uint8, uint16, uint32, uint64, uint128,
float, double, longdouble, cfloat (complex float), cdouble (complex double),
clongdouble (complex long double), float16, float32, float64, float80,
float128, decimal32, decimal64 and decimal128. Note that some of these types
are only available with specific architectures and compiler versions.

Function return stressor
--funcret N
start N workers that pass and return by value various small to large data
types.

--funcret-ops N
stop the funcret workers after N bogo function call operations.

--funcret-method method
specify the method of funcret argument type to be used. The default is
uint64_t but can be one of uint8 uint16 uint32 uint64 uint128 float double
longdouble float80 float128 decimal32 decimal64 decimal128 uint8x32 uint8x128
uint64x128.

Fast mutex (futex) stressor
--futex N
start N workers that rapidly exercise the futex system call. Each worker has
two processes, a futex waiter and a futex waker. The waiter waits with a very
small timeout to stress the timeout and rapid polled futex waiting. This is a
Linux specific stress option.

--futex-ops N
stop futex workers after N bogo successful futex wait operations.

Fetching data from kernel stressor
--get N
start N workers that call system calls that fetch data from the kernel,
currently these are: getpid, getppid, getcwd, getgid, getegid, getuid,
getgroups, getpgrp, getpgid, getpriority, getresgid, getresuid, getrlimit,
prlimit, getrusage, getsid, gettid, getcpu, gettimeofday, uname, adjtimex,
sysfs. Some of these system calls are OS specific.

--get-ops N
stop get workers after N bogo get operations.

Virtual filesystem directories stressor (Linux)
--getdent N
start N workers that recursively read directories /proc, /dev/, /tmp, /sys and
/run using getdents and getdents64 (Linux only).

--getdent-ops N
stop getdent workers after N bogo getdent bogo operations.

Random data (getrandom) stressor
--getrandom N
start N workers that get 8192 random bytes from the /dev/urandom pool using
the getrandom(2) system call (Linux) or getentropy(2) (OpenBSD).

--getrandom-ops N
stop getrandom workers after N bogo get operations.

CPU pipeline and branch prediction stressor
--goto N
start N workers that perform 1024 forward branches (to next instruction) or
backward branches (to previous instruction) for each bogo operation loop. By
default, every 1024 branches the direction is randomly chosen to be forward or
backward. This stressor exercises suboptimal pipelined execution and branch
prediction logic.

--goto-direction [ forward | backward | random ]
select the branching direction in the stressor loop, forward for forward only
branching, backward for a backward only branching, random for a random choice
of forward or random branching every 1024 branches.

--goto-ops N
stop goto workers after N bogo loops of 1024 branch instructions.

2D GPU stressor
--gpu N
start N worker that exercise the GPU. This specifies a 2-D texture image that
allows the elements of an image array to be read by shaders, and render
primitives using an opengl context.

--gpu-devnode DEVNAME
specify the device node name of the GPU device, the default is
/dev/dri/renderD128.

--gpu-frag N
specify shader core usage per pixel, this sets N loops in the fragment shader.

--gpu-ops N
stop gpu workers after N render loop operations.

--gpu-tex-size N
specify upload texture N × N, by default this value is 4096 × 4096.

--gpu-xsize X
use a framebuffer size of X pixels. The default is 256 pixels.

--gpu-ysize Y
use a framebuffer size of Y pixels. The default is 256 pixels.

--gpu-upload N
specify upload texture N times per frame, the default value is 1.

Handle stressor
--handle N
start N workers that exercise the name_to_handle_at(2) and
open_by_handle_at(2) system calls. (Linux only).

--handle-ops N
stop after N handle bogo operations.

String hashing stressor
--hash N
start N workers that exercise various hashing functions. Random strings from 1
to 128 bytes are hashed and the hashing rate and chi squared is calculated
from the number of hashes performed over a period of time. The chi squared
value is the goodness-of-fit measure, it is the actual distribution of items
in hash buckets versus the expected distribution of items. Typically a chi
squared value of 0.95..1.05 indicates a good hash distribution.

--hash-method method
specify the hashing method to use, by default all the hashing methods are
cycled through. Methods available are:

Method Description
all cycle through all the hashing methods
adler32 Mark Adler checksum, a modification of the Fletcher checksum
coffin xor and 5 bit rotate left hash
coffin32 xor and 5 bit rotate left hash with 32 bit fetch optimization
crc32c compute CRC32C (Castagnoli CRC32) integer hash
djb2a Dan Bernstein hash using the xor variant
fnv1a FNV-1a Fowler-Noll-Vo hash using the xor then multiply variant
jenkin Jenkin's integer hash
kandr Kernighan and Richie's multiply by 31 and add hash from "The C
Programming Language", 2nd Edition
knuth Donald E. Knuth's hash from "The Art Of Computer Programming",
Volume 3, chapter 6.4
loselose Kernighan and Richie's simple hash from "The C Programming
Language", 1st Edition
mid5 xor shift hash of the middle 5 characters of the string. Designed
by Colin Ian King
muladd32 simple multiply and add hash using 32 bit math and xor folding of
overflow
muladd64 simple multiply and add hash using 64 bit math and xor folding of
overflow

mulxror32 32 bit multiply, xor and rotate right. Mangles 32 bits where
possible. Designed by Colin Ian King
mulxror64 64 bit multiply, xor and rotate right. 64 Bit version of mulxror32
murmur3_32 murmur3_32 hash, Austin Appleby's Murmur3 hash, 32 bit variant
nhash exim's nhash.
pjw a non-cryptographic hash function created by Peter J. Weinberger
of AT&T Bell Labs, used in UNIX ELF object files
sdbm sdbm hash as used in the SDBM database and GNU awk
sedgwick simple hash from Robert Sedgwick's C programming book
sobel Justin Sobel's bitwise shift hash
x17 multiply by 17 and add. The multiplication can be optimized down
to a fast right shift by 4 and add on some architectures
xor simple rotate shift and xor of values
xorror32 32 bit exclusive-or with right rotate hash, a fast string hash,
designed by Colin Ian King
xorror64 64 bit version of xorror32
xxhash the "Extremely fast" hash in non-streaming mode

--hash-ops N
stop after N hashing rounds

File-system stressor
-d N, --hdd N
start N workers continually writing, reading and removing temporary files. The
default mode is to stress test sequential writes and reads. With the
--aggressive option enabled without any --hdd-opts options the hdd stressor
will work through all the --hdd-opt options one by one to cover a range of I/O
options.

--hdd-bytes N
write N bytes for each hdd process, the default is 1 GB. One can specify the
size as % of free space on the file system or in units of Bytes, KBytes,
MBytes and GBytes using the suffix b, k, m or g.

--hdd-opts list
specify various stress test options as a comma separated list. Options are as
follows:

Option Description
direct try to minimize cache effects of the I/O. File I/O writes are
performed directly from user space buffers and synchronous
transfer is also attempted. To guarantee synchronous I/O,
also use the sync option.
dsync ensure output has been transferred to underlying hardware and
file metadata has been updated (using the O_DSYNC open flag).
This is equivalent to each write(2) being followed by a call
to fdatasync(2). See also the fdatasync option.
fadv-dontneed advise kernel to expect the data will not be accessed in the
near future.
fadv-noreuse advise kernel to expect the data to be accessed only once.
fadv-normal advise kernel there are no explicit access pattern for the
data. This is the default advice assumption.
fadv-rnd advise kernel to expect random access patterns for the data.
fadv-seq advise kernel to expect sequential access patterns for the
data.
fadv-willneed advise kernel to expect the data to be accessed in the near
future.
fsync flush all modified in-core data after each write to the output
device using an explicit fsync(2) call.
fdatasync similar to fsync, but do not flush the modified metadata
unless metadata is required for later data reads to be handled
correctly. This uses an explicit fdatasync(2) call.
iovec use readv/writev multiple buffer I/Os rather than read/write.
Instead of 1 read/write operation, the buffer is broken into
an iovec of 16 buffers.
noatime do not update the file last access timestamp, this can reduce
metadata writes.
sync ensure output has been transferred to underlying hardware
(using the O_SYNC open flag). This is equivalent to a each
write(2) being followed by a call to fsync(2). See also the
fsync option.
rd-rnd read data randomly. By default, written data is not read back,
however, this option will force it to be read back randomly.
rd-seq read data sequentially. By default, written data is not read
back, however, this option will force it to be read back
sequentially.
syncfs write all buffered modifications of file metadata and data on
the filesystem that contains the hdd worker files.
utimes force update of file timestamp which may increase metadata
writes.

wr-rnd write data randomly. The wr-seq option cannot be used at the
same time.
wr-seq write data sequentially. This is the default if no write modes
are specified.

Note that some of these options are mutually exclusive, for example, there can be
only one method of writing or reading. Also, fadvise flags may be mutually
exclusive, for example fadv-willneed cannot be used with fadv-dontneed.

--hdd-ops N
stop hdd stress workers after N bogo operations.

--hdd-write-size N
specify size of each write in bytes. Size can be from 1 byte to 4MB.

BSD heapsort stressor
--heapsort N
start N workers that sort 32 bit integers using the BSD heapsort.

--heapsort-method [ heapsort-libc | heapsort-nonlibc ]
select either the libc implementation of heapsort or an optimized
implementation of heapsort. The default is the libc implementation if it is
available.

--heapsort-ops N
stop heapsort stress workers after N bogo heapsorts.

--heapsort-size N
specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

High resolution timer stressor
--hrtimers N
start N workers that exercise high resolution times at a high frequency. Each
stressor starts 32 processes that run with random timer intervals of 0..499999
nanoseconds. Running this stressor with appropriate privilege will run these
with the SCHED_RR policy.

--hrtimers-adjust
enable automatic timer rate adjustment to try to maximize the hrtimer
frequency. The signal rate is measured every 0.1 seconds and the hrtimer
delay is adjusted to try and set the optimal hrtimer delay to generate the
highest hrtimer rates.

--hrtimers-ops N
stop hrtimers stressors after N timer event bogo operations

Hashtable searching (hsearch) stressor
--hsearch N
start N workers that search a 80% full hash table using hsearch(3). By
default, there are 8192 elements inserted into the hash table. This is a
useful method to exercise access of memory and processor cache.

--hsearch-method [ hsearch-libc | hsearch-nonlibc ]
select either the libc implementation of hsearch or a slightly optimized non-
libc implementation of hsearch. The default is the libc implementation if it
exists, otherwise the non-libc version.

--hsearch-ops N
stop the hsearch workers after N bogo hsearch operations are completed.

--hsearch-size N
specify the number of hash entries to be inserted into the hash table. Size
can be from 1K to 4M.

CPU instruction cache load stressor
--icache N
start N workers that stress the instruction cache by forcing instruction cache
reloads.

--icache-ops N
stop the icache workers after N bogo icache operations are completed.

ICMP flooding stressor
--icmp-flood N
start N workers that flood localhost with randonly sized ICMP ping packets.
This stressor requires the CAP_NET_RAW capbility.

--icmp-flood-ops N
stop icmp flood workers after N ICMP ping packets have been sent.

Idle pages stressor (Linux)
--idle-scan N
start N workers that scan the idle page bitmap across a range of physical
pages. This sets and checks for idle pages via the idle page tracking
interface /sys/kernel/mm/page_idle/bitmap. This is for Linux only.

--idle-scan-ops N
stop after N bogo page scan operations. Currently one bogo page scan operation
is equivalent to setting and checking 64 physical pages.

--idle-page N
start N workers that walks through every page exercising the Linux
/sys/kernel/mm/page_idle/bitmap interface. Requires CAP_SYS_RESOURCE
capability.

--idle-page-ops N
stop after N bogo idle page operations.

Inode ioctl flags stressor
--inode-flags N
start N workers that exercise inode flags using the FS_IOC_GETFLAGS and
FS_IOC_SETFLAGS ioctl(2). This attempts to apply all the available inode flags
onto a directory and file even if the underlying file system may not support
these flags (errors are just ignored). Each worker runs 4 threads that
exercise the flags on the same directory and file to try to force races. This
is a Linux only stressor, see ioctl_iflags(2) for more details.

--inode-flags-ops N
stop the inode-flags workers after N ioctl flag setting attempts.

Inotify stressor
--inotify N
start N workers performing file system activities such as making/deleting
files/directories, moving files, etc. to stress exercise the various inotify
events (Linux only).

--inotify-ops N
stop inotify stress workers after N inotify bogo operations.

Data synchronization (sync) stressor
-i N, --io N
start N workers continuously calling sync(2) to commit buffer cache to disk.
This can be used in conjunction with the --hdd stressor. This is a legacy
stressor that is compatible with the original stress tool.

--io-ops N
stop io stress workers after N bogo operations.

IO mixing stressor
--iomix N
start N workers that perform a mix of sequential, random and memory mapped
read/write operations as well as random copy file read/writes, forced sync'ing
and (if run as root) cache dropping. Multiple child processes are spawned to
all share a single file and perform different I/O operations on the same file.

--iomix-bytes N
write N bytes for each iomix worker process, the default is 1 GB. One can
specify the size as % of free space on the file system or in units of Bytes,
KBytes, MBytes and GBytes using the suffix b, k, m or g.

--iomix-ops N
stop iomix stress workers after N bogo iomix I/O operations.

Ioport stressor (x86 Linux)
--ioport N
start N workers than perform bursts of 16 reads and 16 writes of ioport 0x80
(x86 Linux systems only). I/O performed on x86 platforms on port 0x80 will
cause delays on the CPU performing the I/O.

--ioport-ops N
stop the ioport stressors after N bogo I/O operations

--ioport-opts [ in | out | inout ]
to be performed. The default is both in and out. specify if port reads in,
port read writes out or reads and writes are

IO scheduling class and priority stressor
--ioprio N
start N workers that exercise the ioprio_get(2) and ioprio_set(2) system calls
(Linux only).

--ioprio-ops N
stop after N io priority bogo operations.

Io-uring stressor
--io-uring N
start N workers that perform iovec write and read I/O operations using the
Linux io-uring interface. On each bogo-loop 1024 × 512 byte writes and 1024 ×
reads are performed on a temporary file.

--io-uring-entries N
specify the number of io-uring ring entries.

--io-uring-ops
stop after N rounds of write and reads.

Ipsec multi-buffer cryptographic stressor
--ipsec-mb N
start N workers that perform cryptographic processing using the highly
optimized Intel Multi-Buffer Crypto for IPsec library. Depending on the
features available, SSE, AVX, AVX and AVX512 CPU features will be used on data
encrypted by SHA, DES, CMAC, CTR, HMAC MD5, HMAC SHA1 and HMAC SHA512
cryptographic routines. This is only available for x86-64 modern Intel CPUs.

--ipsec-mb-feature [ sse | avx | avx2 | avx512 ]
Just use the specified processor CPU feature. By default, all the available
features for the CPU are exercised.

--ipsec-mb-jobs N
Process N multi-block rounds of cryptographic processing per iteration. The
default is 256.

--ipsec-mb-ops N
stop after N rounds of processing of data using the cryptographic routines.

System interval timer stressor
--itimer N
start N workers that exercise the system interval timers. This sets up an
ITIMER_PROF itimer that generates a SIGPROF signal. The default frequency for
the itimer is 1 MHz, however, the Linux kernel will set this to be no more
that the jiffy setting, hence high frequency SIGPROF signals are not normally
possible. A busy loop spins on getitimer(2) calls to consume CPU and hence
decrement the itimer based on amount of time spent in CPU and system time.

--itimer-freq F
run itimer at F Hz; range from 1 to 1000000 Hz. Normally the highest frequency
is limited by the number of jiffy ticks per second, so running above 1000 Hz
is difficult to attain in practice.

--itimer-ops N
stop itimer stress workers after N bogo itimer SIGPROF signals.

--itimer-rand
select an interval timer frequency based around the interval timer frequency
+/- 12.5% random jitter. This tries to force more variability in the timer
interval to make the scheduling less predictable.

Jpeg compression stressor
--jpeg N
start N workers that use jpeg compression on a machine generated plasma field
image. The default image is a plasma field, however different image types may
be selected. The starting raster line is changed on each compression iteration
to cycle around the data.

--jpeg-height H
use a RGB sample image height of H pixels. The default is 512 pixels.

Type Description
brown brown noise, red and green values vary by a 3 bit value, blue values
vary by a 2 bit value.
flat a single random colour for the entire image.
gradient linear gradient of the red, green and blue components across the
width and height of the image.
noise random white noise for red, green, blue values.
plasma plasma field with smooth colour transitions and hard boundary edges.
xstripes a random colour for each horizontal line.

--jpeg-ops N
stop after N jpeg compression operations.

--jpeg-quality Q
use the compression quality Q. The range is 1..100 (1 lowest, 100 highest),
with a default of 95

--jpeg-width H
use a RGB sample image width of H pixels. The default is 512 pixels.

Judy array stressor
--judy N
start N workers that insert, search and delete 32 bit integers in a Judy array
using a predictable yet sparse array index. By default, there are 131072
integers used in the Judy array. This is a useful method to exercise random
access of memory and processor cache.

--judy-ops N
stop the judy workers after N bogo judy operations are completed.

--judy-size N
specify the size (number of 32 bit integers) in the Judy array to exercise.
Size can be from 1K to 4M 32 bit integers.

Kcmp stressor (Linux)
--kcmp N
start N workers that use kcmp(2) to compare parent and child processes to
determine if they share kernel resources. Supported only for Linux and
requires CAP_SYS_PTRACE capability.

--kcmp-ops N
stop kcmp workers after N bogo kcmp operations.

Kernel key management stressor
--key N
start N workers that create and manipulate keys using add_key(2) and
ketctl(2). As many keys are created as the per user limit allows and then the
following keyctl commands are exercised on each key: KEYCTL_SET_TIMEOUT,
KEYCTL_DESCRIBE, KEYCTL_UPDATE, KEYCTL_READ, KEYCTL_CLEAR and
KEYCTL_INVALIDATE.

--key-ops N
stop key workers after N bogo key operations.

Process signals stressor
--kill N
start N workers sending SIGUSR1 kill signals to a SIG_IGN signal handler in
the stressor and SIGUSR1 kill signal to a child stressor with a SIGUSR1
handler. Most of the process time will end up in kernel space.

--kill-ops N
stop kill workers after N bogo kill operations.

Syslog stressor (Linux)
--klog N
start N workers exercising the kernel syslog(2) system call. This will
attempt to read the kernel log with various sized read buffers. Linux only.

--klog-ops N
stop klog workers after N syslog operations.

KVM stressor
--kvm N
start N workers that create, run and destroy a minimal virtual machine. The
virtual machine reads, increments and writes to port 0x80 in a spin loop and
the stressor handles the I/O transactions. Currently for x86 and Linux only.

--kvm-ops N
stop kvm stressors after N virtual machines have been created, run and
destroyed.

CPU L1 cache stressor
--l1cache N
start N workers that exercise the CPU level 1 cache with reads and writes. A
cache aligned buffer that is twice the level 1 cache size is read and then
written in level 1 cache set sized steps over each level 1 cache set. This is
designed to exercise cache block evictions. The bogo-op count measures the
number of million cache lines touched. Where possible, the level 1 cache
geometry is determined from the kernel, however, this is not possible on some
architectures or kernels, so one may need to specify these manually. One can
specify 3 out of the 4 cache geometric parameters, these are as follows:

--l1cache-line-size N
specify the level 1 cache line size (in bytes)

--l1cache-method [ forward | random | reverse ]
select the method of exercising a l1cache sized buffer. The default is a
forward scan, random picks random bytes to exercise, reverse scans in reverse.

--l1cache-mlock
attempt to mlock the l1cache size buffer into memory to prevent it from being
swapped out.

--l1cache-ops N
specify the number of cache read/write bogo-op loops to run

--l1cache-sets N
specify the number of level 1 cache sets

--l1cache-size N
specify the level 1 cache size (in bytes)

--l1cache-ways N
specify the number of level 1 cache ways

Landlock stressor (Linux >= 5.13)
--landlock N
start N workers that exercise Linux 5.13 landlocking. A range of
landlock_create_ruleset flags are exercised with a read only file rule to see
if a directory can be accessed and a read-write file create can be blocked.
Each ruleset attempt is exercised in a new child context and this is the
limiting factor on the speed of the stressor.

--landlock-ops N
stop the landlock stressors after N landlock ruleset bogo operations.

File lease stressor
--lease N
start N workers locking, unlocking and breaking leases via the fcntl(2)
F_SETLEASE operation. The parent processes continually lock and unlock a lease
on a file while a user selectable number of child processes open the file with
a non-blocking open to generate SIGIO lease breaking notifications to the
parent. This stressor is only available if F_SETLEASE, F_WRLCK and F_UNLCK
support is provided by fcntl(2).

--lease-breakers N
start N lease breaker child processes per lease worker. Normally one child is
plenty to force many SIGIO lease breaking notification signals to the parent,
however, this option allows one to specify more child processes if required.

--lease-ops N
stop lease workers after N bogo operations.

LED stressor (Linux)
--led N
start N workers that exercise the /sys/class/leds interfaces to set LED
brightness levels and the various trigger settings. This needs to be run with
root privilege to be able to write to these settings successfully. Non-root
privilege will ignore failed writes.

--led-ops N
stop after N interfaces are exercised.

Hardlink stressor
--link N
start N workers creating and removing hardlinks.

--link-ops N
stop link stress workers after N bogo operations.

--link-sync
sync dirty data and metadata to disk.

List data structures stressor
--list N
start N workers that exercise list data structures. The default is to add,
find and remove 5,000 64 bit integers into circleq (doubly linked circle
queue), list (doubly linked list), slist (singly linked list), slistt (singly
linked list using tail), stailq (singly linked tail queue) and tailq (doubly
linked tail queue) lists. The intention of this stressor is to exercise memory
and cache with the various list operations.

--list-ops N
stop list stressors after N bogo ops. A bogo op covers the addition, finding
and removing all the items into the list(s).

--list-size N
specify the size of the list, where N is the number of 64 bit integers to be
added into the list.

Last level of cache stressor
--llc-affinity N
start N workers that exercise the last level of cache (LLC) by read/write
activity across a LLC sized buffer and then changing CPU affinity after each
round of read/writes. This can cause non-local memory stalls and LLC
read/write misses.

--llc-affinity-mlock
attempt to mlock the LLC sized buffer into memory to prevent it from being
swapped out.

--llc-affinity-ops N
stop after N rounds of LLC read/writes.

Load average (loadavg) stressor
--loadavg N
start N workers that attempt to create thousands of pthreads that run at the
lowest nice priority to force very high load averages. Linux systems will also
perform some I/O writes as pending I/O is also factored into system load
accounting.

--loadavg-max N
set the maximum number of pthreads to create to N. N may be reduced if there
is as system limit on the number of pthreads that can be created.

--loadavg-ops N
stop loadavg workers after N bogo scheduling yields by the pthreads have been
reached.

Lock and increment memory stressor (x86 and ARM)
--lockbus N
start N workers that rapidly lock and increment 64 bytes of randomly chosen
memory from a 16MB mmap'd region (Intel x86 and ARM CPUs only). This will
cause cacheline misses and stalling of CPUs.

--lockbus-nosplit
disable split locks that lock across cache line boundaries.

--lockbus-ops N
stop lockbus workers after N bogo operations.

POSIX lock (F_SETLK/F_GETLK) stressor
--locka N
start N workers that randomly lock and unlock regions of a file using the
POSIX advisory locking mechanism (see fcntl(2), F_SETLK, F_GETLK). Each worker
creates a 1024 KB file and attempts to hold a maximum of 1024 concurrent locks
with a child process that also tries to hold 1024 concurrent locks. Old locks
are unlocked in a first-in, first-out basis.

--locka-ops N
stop locka workers after N bogo locka operations.

POSIX lock (lockf) stressor
--lockf N
start N workers that randomly lock and unlock regions of a file using the
POSIX lockf(3) locking mechanism. Each worker creates a 64 KB file and
attempts to hold a maximum of 1024 concurrent locks with a child process that
also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-
in, first-out basis.

--lockf-nonblock
instead of using blocking F_LOCK lockf(3) commands, use non-blocking F_TLOCK
commands and re-try if the lock failed. This creates extra system call
overhead and CPU utilisation as the number of lockf workers increases and
should increase locking contention.

--lockf-ops N
stop lockf workers after N bogo lockf operations.

POSIX lock (F_OFD_SETLK/F_OFD_GETLK) stressor
--lockofd N
start N workers that randomly lock and unlock regions of a file using the
Linux open file description locks (see fcntl(2), F_OFD_SETLK, F_OFD_GETLK).
Each worker creates a 1024 KB file and attempts to hold a maximum of 1024
concurrent locks with a child process that also tries to hold 1024 concurrent
locks. Old locks are unlocked in a first-in, first-out basis.

--lockofd-ops N
stop lockofd workers after N bogo lockofd operations.

Long jump (longjmp) stressor
--longjmp N
start N workers that exercise setjmp(3)/longjmp(3) by rapid looping on longjmp
calls.

--longjmp-ops N
stop longjmp stress workers after N bogo longjmp operations (1 bogo op is 1000
longjmp calls).

Loopback stressor (Linux)
--loop N
start N workers that exercise the loopback control device. This creates 2MB
loopback devices, expands them to 4MB, performs some loopback status
information get and set operations and then destoys them. Linux only and
requires CAP_SYS_ADMIN capability.

--loop-ops N
stop after N bogo loopback creation/deletion operations.

Linear search stressor
--lsearch N
start N workers that linear search a unsorted array of 32 bit integers using
lsearch(3). By default, there are 8192 elements in the array. This is a
useful method to exercise sequential access of memory and processor cache.

--lsearch-method [ lsearch-libc | lsearch-nonlibc ]
select either the libc implementation of lsearch or a slightly optimized non-
libc implementation of lsearch. The default is the libc implementation if it
exists, otherwise the non-libc version.

--lsearch-ops N
stop the lsearch workers after N bogo lsearch operations are completed.

--lsearch-size N
specify the size (number of 32 bit integers) in the array to lsearch. Size can
be from 1K to 4M.

Madvise stressor
--madvise N
start N workers that apply random madvise(2) advise settings on pages of a 4MB
file backed shared memory mapping.

--madvise-hwpoison
enable MADV_HWPOISON page poisoning (if available, only when run as root).
This will page poison a few pages and will cause kernel error messages to be
reported.

--madvise-ops N
stop madvise stressors after N bogo madvise operations.

Memory allocation stressor
--malloc N
start N workers continuously calling malloc(3), calloc(3), realloc(3),
posix_memalign(3), aligned_alloc(3), memalign(3) and free(3). By default, up
to 65536 allocations can be active at any point, but this can be altered with
the --malloc-max option. Allocation, reallocation and freeing are chosen at
random; 50% of the time memory is allocation (via one of malloc, calloc or
realloc, posix_memalign, aligned_alloc, memalign) and 50% of the time
allocations are free'd. Allocation sizes are also random, with the maximum
allocation size controlled by the --malloc-bytes option, the default size
being 64K. The worker is re-started if it is killed by the out of memory
(OOM) killer.

--malloc-bytes N
maximum per allocation/reallocation size. Allocations are randomly selected
from 1 to N bytes. One can specify the size as % of total available memory or
in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.
Large allocation sizes cause the memory allocator to use mmap(2) rather than
expanding the heap using brk(2).

--malloc-max N
maximum number of active allocations allowed. Allocations are chosen at random
and placed in an allocation slot. Because about 50%/50% split between
allocation and freeing, typically half of the allocation slots are in use at
any one time.

--malloc-mlock
attempt to mlock the allocations into memory to prevent them from being
swapped out.

--malloc-ops N
stop after N malloc bogo operations. One bogo operations relates to a
successful malloc(3), calloc(3) or realloc(3).

--malloc-pthreads N
specify number of malloc stressing concurrent pthreads to run. The default is
0 (just one main process, no pthreads). This option will do nothing if
pthreads are not supported.

--malloc-thresh N
specify the threshold where malloc uses mmap(2) instead of sbrk(2) to allocate
more memory. This is only available on systems that provide the GNU C
mallopt(3) tuning function.

--malloc-touch
touch every allocated page to force pages to be populated in memory. This will
increase the memory pressure and exercise the virtual memory harder. By
default the malloc stressor will madvise pages into memory or use mincore to
check for non-resident memory pages and try to force them into memory; this
option aggressively forces pages to be memory resident.

--malloc-trim
periodically trim memory allocation by attempting to release free memory from
the heap every 65536 allocation iterations. This can be a time consuming
operation. It is only available with libc malloc implementations that support
malloc_trim(3).

--malloc-zerofree
zero allocated memory before free'ing. This can be useful in touching broken
allocations and triggering failures. Also useful for forcing extra
cache/memory writes.

2D Matrix stressor
--matrix N
start N workers that perform various matrix operations on floating point
values. Testing on 64 bit x86 hardware shows that this provides a good mix of
memory, cache and floating point operations and is an excellent way to make a
CPU run hot.

By default, this will exercise all the matrix stress methods one by one. One
can specify a specific matrix stress method with the --matrix-method option.

--matrix-method method
specify a matrix stress method. Available matrix stress methods are described
as follows:

Method Description
all iterate over all the below matrix stress methods
add add two N × N matrices
copy copy one N × N matrix to another
div divide an N × N matrix by a scalar
frobenius Frobenius product of two N × N matrices
hadamard Hadamard product of two N × N matrices
identity create an N × N identity matrix
mean arithmetic mean of two N × N matrices
mult multiply an N × N matrix by a scalar
negate negate an N × N matrix
prod product of two N × N matrices
sub subtract one N × N matrix from another N × N matrix
square multiply an N × N matrix by itself
trans transpose an N × N matrix
zero zero an N × N matrix

--matrix-ops N
stop matrix stress workers after N bogo operations.

--matrix-size N
specify the N × N size of the matrices. Smaller values result in a floating
point compute throughput bound stressor, where as large values result in a
cache and/or memory bandwidth bound stressor.

--matrix-yx
perform matrix operations in order y by x rather than the default x by y. This
is suboptimal ordering compared to the default and will perform more data
cache stalls.

3D Matrix stressor
--matrix-3d N
start N workers that perform various 3D matrix operations on floating point
values. Testing on 64 bit x86 hardware shows that this provides a good mix of
memory, cache and floating point operations and is an excellent way to make a
CPU run hot.

By default, this will exercise all the 3D matrix stress methods one by one.
One can specify a specific 3D matrix stress method with the --matrix-3d-method
option.

--matrix-3d-method method
specify a 3D matrix stress method. Available 3D matrix stress methods are
described as follows:

Method Description
all iterate over all the below matrix stress methods
add add two N × N × N matrices
copy copy one N × N × N matrix to another
div divide an N × N × N matrix by a scalar
frobenius Frobenius product of two N × N × N matrices
hadamard Hadamard product of two N × N × N matrices
identity create an N × N × N identity matrix
mean arithmetic mean of two N × N × N matrices
mult multiply an N × N × N matrix by a scalar
negate negate an N × N × N matrix
sub subtract one N × N × N matrix from another N × N × N matrix
trans transpose an N × N × N matrix
zero zero an N × N × N matrix

--matrix-3d-ops N
stop the 3D matrix stress workers after N bogo operations.

--matrix-3d-size N
specify the N × N × N size of the matrices. Smaller values result in a
floating point compute throughput bound stressor, where as large values result
in a cache and/or memory bandwidth bound stressor.

--matrix-3d-zyx
perform matrix operations in order z by y by x rather than the default x by y
by z. This is suboptimal ordering compared to the default and will perform
more data cache stalls.

Memory contention stressor
--mcontend N
start N workers that produce memory contention read/write patterns. Each
stressor runs with 5 threads that read and write to two different mappings of
the same underlying physical page. Various caching operations are also
exercised to cause sub-optimal memory access patterns. The threads also
randomly change CPU affinity to exercise CPU and memory migration stress.

--mcontend-ops N
stop mcontend stressors after N bogo read/write operations.

Memory barrier stressor (Linux)
--membarrier N
start N workers that exercise the membarrier system call (Linux only).

--membarrier-ops N
stop membarrier stress workers after N bogo membarrier operations.

Memory copy (memcpy) stressor
--memcpy N
start N workers that copies data to and from a buffer using memcpy(3) and then
move the data in the buffer with memmove(3) with 3 different alignments. This
will exercise the data cache and memory copying.

--memcpy-method [ all | libc | builtin | naive | naive_o0 .. naive_o3 ]
specify a memcpy copying method. Available memcpy methods are described as
follows:

Method Description
all use libc, builtin and naïve methods
libc use libc memcpy and memmove functions, this is the default
builtin use the compiler built in optimized memcpy and memmove functions
naive use naïve byte by byte copying and memory moving build with default
compiler optimization flags
naive_o0 use unoptimized naïve byte by byte copying and memory moving
naive_o1 use unoptimized naïve byte by byte copying and memory moving with
-O1 optimization
naive_o2 use optimized naïve byte by byte copying and memory moving build
with -O2 optimization and where possible use CPU specific
optimizations
naive_o3 use optimized naïve byte by byte copying and memory moving build
with -O3 optimization and where possible use CPU specific
optimizations

--memcpy-ops N
stop memcpy stress workers after N bogo memcpy operations.

Anonymous file (memfd) stressor
--memfd N
start N workers that create allocations of 1024 pages using memfd_create(2)
and ftruncate(2) for allocation and mmap(2) to map the allocation into the
process address space. (Linux only).

--memfd-bytes N
allocate N bytes per memfd stress worker, the default is 256MB. One can
specify the size in as % of total available memory or in units of Bytes,
KBytes, MBytes and GBytes using the suffix b, k, m or g.

--memfd-fds N
create N memfd file descriptors, the default is 256. One can select 8 to 4096
memfd file descriptions with this option.

--memfd-madvise
enable random madvise page advice on memfd memory mapped regions to add a
little more VM exercising.

--memfd-mlock
attempt to mlock mmap'd pages into memory causing more memory pressure by
preventing pages from swapped out.

--memfd-ops N
stop after N memfd-create(2) bogo operations.

--memfd-zap-pte
exercise zapping page-table-entries to try to reproduce a Linux kernel bug
that was fixed by commit 5abfd71d936a8aefd9f9ccd299dea7a164a5d455 "mm: don't
skip swap entry even if zap_details specified". This will slow the stressor
down significantly and hence is an opt-in memfd stressor option.

Memory hotplug stressor (Linux)
--memhotplug N
start N workers that offline and online memory hotplug regions. Linux only and
requires CAP_SYS_ADMIN capabilities.

--memhotplug-ops N
stop memhotplug stressors after N memory offline and online bogo operations.

Memory read/write stressor
--memrate N
start N workers that exercise a buffer with 1024, 512, 256, 128, 64, 32, 16
and 8 bit reads and writes. 1024, 512 and 256 reads and writes are available
with compilers that support integer vectors. x86-64 cpus that support
uncached (non-temporal "nt") writes also exercise 128, 64 and 32 writes
providing higher write rates than the normal cached writes. x86-64 also
exercises repeated string stores using 64, 32, 16 and 8 bit writes. CPUs that
support prefetching reads also exercise 64 prefetched "pf" reads. This memory
stressor allows one to also specify the maximum read and write rates. The
stressors will run at maximum speed if no read or write rates are specified.

--memrate-bytes N
specify the size of the memory buffer being exercised. The default size is
256MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g, or cache sizes with L1, L2, L3 or LLC (lower
level cache size).

--memrate-flush
flush cache between each memory exercising test to remove caching benefits in
memory rate metrics.

--memrate-ops N
stop after N bogo memrate operations.

--memrate-rd-mbs N
specify the maximum allowed read rate in MB/sec. The actual read rate is
dependent on scheduling jitter and memory accesses from other running
processes.

--memrate-wr-mbs N
specify the maximum allowed read rate in MB/sec. The actual write rate is
dependent on scheduling jitter and memory accesses from other running
processes.

Memory thrash stressor
--memthrash N
start N workers that thrash and exercise a 16MB buffer in various ways to try
and trip thermal overrun. Each stressor will start 1 or more threads. The
number of threads is chosen so that there will be at least 1 thread per CPU.
Note that the optimal choice for N is a value that divides into the number of
CPUs.

--memthrash-method method
specify a memthrash stress method. Available memthrash stress methods are
described as follows:

Method Description
all iterate over all the below memthrash methods
chunk1 memset 1 byte chunks of random data into random locations
chunk8 memset 8 byte chunks of random data into random locations
chunk64 memset 64 byte chunks of random data into random locations
chunk256 memset 256 byte chunks of random data into random locations
chunkpage memset page size chunks of random data into random locations
copy128 copy 128 byte chunks from chunk N + 1 to chunk N with streaming
reads and writes with 128 bit memory accesses where possible.
flip flip (invert) all bits in random locations
flush flush cache line in random locations
lock lock randomly choosing locations (Intel x86 and ARM CPUs only)
matrix treat memory as a 2 × 2 matrix and swap random elements
memmove copy all the data in buffer to the next memory location
memset memset the memory with random data
memset64 memset the memory with a random 64 bit value in 64 byte chunks
using non-temporal stores if possible or normal stores as a
fallback
memsetstosd memset the memory using x86 32 bit rep stosd instruction (x86
only)
mfence stores with write serialization
numa memory bind pages across numa nodes
prefetch prefetch data at random memory locations
random randomly run any of the memthrash methods except for 'random' and
'all'
reverse swap 8 bit values from start to end and work towards the middle
spinread spin loop read the same random location 2↑19 times
spinwrite spin loop write the same random location 2↑19 times
swap step through memory swapping bytes in steps of 65 and 129 byte
strides
swap64 work through memory swapping adjacent 64 byte chunks
swapfwdrev swap 64 bit values from start to end and work towards the middle
and then from end to start and work towards the middle.
tlb work through memory in sub-optimial strides of prime multiples of
the cache line size with reads and then writes to cause
Translation Lookaside Buffer (TLB) misses.

--memthrash-ops N
stop after N memthrash bogo operations.

BSD mergesort stressor
--mergesort N
start N workers that sort 32 bit integers using the BSD mergesort.

--mergesort-method [ mergesort-libc | mergesort-nonlibc ]
select either the libc implementation of mergesort or an unoptimized
implementation of mergesort. The default is the libc implementation if it is
available.

--mergesort-ops N
stop mergesort stress workers after N bogo mergesorts.

--mergesort-size N
specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

File metadata mix
--metamix N
start N workers that generate a file metadata mix of operations. Each stressor
runs 16 concurrent processes that each exercise a file's metadata with
sequences of open, 256 lseeks and writes, fdatasync, close, fsync and then
stat, open, 256 lseeks, reads, occasional file memory mapping, close, unlink
and lstat.

--metamix-bytes N
set the size of metamix files, the default is 1 MB. One can specify the size
as % of free space on the file system or in units of Bytes, KBytes, MBytes and
GBytes using the suffix b, k, m or g.

--metamix-ops N
stop the metamix stressor after N bogo metafile operations.

Resident memory (mincore) stressor
--mincore N
start N workers that walk through all of memory 1 page at a time checking if
the page mapped and also is resident in memory using mincore(2). It also maps
and unmaps a page to check if the page is mapped or not using mincore(2).

--mincore-ops N
stop after N mincore bogo operations. One mincore bogo op is equivalent to a
300 mincore(2) calls. --mincore-random instead of walking through pages
sequentially, select pages at random. The chosen address is iterated over by
shifting it right one place and checked by mincore until the address is less
or equal to the page size.

Misaligned read/write stressor
--misaligned N
start N workers that perform misaligned read and writes. By default, this will
exercise 128 bit misaligned read and writes in 8 × 16 bits, 4 × 32 bits, 2 ×
64 bits and 1 × 128 bits at the start of a page boundary, at the end of a page
boundary and over a cache boundary. Misaligned read and writes operate at 1
byte offset from the natural alignment of the data type. On some architectures
this can cause SIGBUS, SIGILL or SIGSEGV, these are handled and the misaligned
stressor method causing the error is disabled.

--misaligned-method method
Available misaligned stress methods are described as follows:

Method Description
all iterate over all the following misaligned methods
int16rd 8 × 16 bit integer reads
int16wr 8 × 16 bit integer writes
int16inc 8 × 16 bit integer increments
int16atomic 8 × 16 bit atomic integer increments
int32rd 4 × 32 bit integer reads
int32wr 4 × 32 bit integer writes
int32wtnt 4 × 32 bit non-temporal stores (x86 only)
int32inc 4 × 32 bit integer increments
int32atomic 4 × 32 bit atomic integer increments
int64rd 2 × 64 bit integer reads
int64wr 2 × 64 bit integer writes
int64wtnt 4 × 64 bit non-temporal stores (x86 only)
int64inc 2 × 64 bit integer increments
int64atomic 2 × 64 bit atomic integer increments
int128rd 1 × 128 bit integer reads
int128wr 1 × 128 bit integer writes
int128inc 1 × 128 bit integer increments
int128atomic 1 × 128 bit atomic integer increments

Note that some of these options (128 bit integer and/or atomic operations) may not be
available on some systems.

--misaligned-ops N
stop after N misaligned bogo operation. A misaligned bogo op is equivalent to
65536 × 128 bit reads or writes.

Mknod/unlink stressor
--mknod N
start N workers that create and remove fifos, empty files and named sockets
using mknod and unlink.

--mknod-ops N
stop directory thrash workers after N bogo mknod operations.

Mapped memory pages lock/unlock stressor
--mlock N
start N workers that lock and unlock memory mapped pages using mlock(2),
munlock(2), mlockall(2) and munlockall(2). This is achieved by the mapping of
three contiguous pages and then locking the second page, hence ensuring non-
contiguous pages are locked . This is then repeated until the maximum allowed
mlocks or a maximum of 262144 mappings are made. Next, all future mappings
are mlocked and the worker attempts to map 262144 pages, then all pages are
munlocked and the pages are unmapped.

--mlock-ops N
stop after N mlock bogo operations.

--mlockmany N
start N workers that fork off a default of 1024 child processes in total; each
child will attempt to anonymously mmap and mlock the maximum allowed mlockable
memory size. The stress test attempts to avoid swapping by tracking low
memory and swap allocations (but some swapping may occur). Once either the
maximum number of child process is reached or all mlockable in-core memory is
locked then child processes are killed and the stress test is repeated.

--mlockmany-ops N
stop after N mlockmany (mmap and mlock) operations.

--mlockmany-procs N
set the number of child processes to create per stressor. The default is to
start a maximum of 1024 child processes in total across all the stressors.
This option allows the setting of N child processes per stressor.

Memory mapping (mmap/munmap) stressor
--mmap N
start N workers continuously calling mmap(2)/munmap(2). The initial mapping
is a large chunk (size specified by --mmap-bytes) followed by pseudo-random 4K
unmappings, then pseudo-random 4K mappings, and then linear 4K unmappings.
Note that this can cause systems to trip the kernel OOM killer on Linux
systems if not enough physical memory and swap is not available. The
MAP_POPULATE option is used to populate pages into memory on systems that
support this. By default, anonymous mappings are used, however, the
--mmap-file and --mmap-async options allow one to perform file based mappings
if desired.

Note that since stress-ng 0.17.05 the --mmap-madvise, --mmap-mergeable,
--mmap-mprotect, --mmap-slow-munmap and --mmap-write-check options should be
used to enable the pre-0.17.05 mmap stressor behaviour.

--mmap-async
enable file based memory mapping and use asynchronous msync'ing on each page,
see --mmap-file.

--mmap-bytes N
allocate N bytes per mmap stress worker, the default is 256MB. One can specify
the size as % of total available memory or in units of Bytes, KBytes, MBytes
and GBytes using the suffix b, k, m or g.

--mmap-file
enable file based memory mapping and by default use synchronous msync'ing on
each page.

--mmap-madvise
enable randomized madvise(2) settings on pages.

--mmap-mergeable
mark pages as mergeable via madvise(2) where possible.

--mmap-mlock
attempt to mlock mmap'd pages into memory causing more memory pressure by
preventing pages from swapped out.

--mmap-mmap2
use mmap2 for 4K page aligned offsets if mmap2 is available, otherwise fall
back to mmap.

--mmap-mprotect
change protection settings on each page of memory. Each time a page or a
group of pages are mapped or remapped then this option will make the pages
read-only, write-only, exec-only, and read-write.

--mmap-odirect
enable file based memory mapping and use O_DIRECT direct I/O.

--mmap-ops N
stop mmap stress workers after N bogo operations.

--mmap-osync
enable file based memory mapping and used O_SYNC synchronous I/O integrity
completion.

--mmap-slow-munmap
enable page-by-page memory unmapping rather than attempting to memory unmap
contiguous pages in one large unmapping. This can cause lock contention when
running with many concurrent mmap stressors and will slow down the stressor.

--mmap-stressful
enable --mmap-file, --mmap-madvise, --mmap-mergeable, --mmap-mlock,
--mmap-mprotect, --mmap-odirect, --mmap-slow-munmap

--mmap-write-check
write into each page a unique 64 bit check value for all pages and then read
the value for a sanity check. This will force newly memory mapped pages to be
faulted-in which slows down mmap bogo-op rate. This can also cause lock
contention on page allocation and page unmapping on systems with many CPU
threads and with cgroup memory accounting.

Random memory map/unmap stressor
--mmapaddr N
start N workers that memory map pages at a random memory location that is not
already mapped. On 64 bit machines the random address is randomly chosen 32
bit or 64 bit address. If the mapping works a second page is memory mapped
from the first mapped address. The stressor exercises mmap/munmap, mincore and
segfault handling.

--mmapaddr-mlock
attempt to mlock mmap'd pages into memory causing more memory pressure by
preventing pages from swapped out.

--mmapaddr-ops N
stop after N random address mmap bogo operations.

Forked memory map stressor
--mmapfork N
start N workers that each fork off 32 child processes, each of which tries to
allocate some of the free memory left in the system (and trying to avoid any
swapping). The child processes then hint that the allocation will be needed
with madvise(2) and then memset it to zero and hint that it is no longer
needed with madvise before exiting. This produces significant amounts of VM
activity, a lot of cache misses and with minimal swapping.

--mmapfork-ops N
stop after N mmapfork bogo operations.

Memory map files stressor
--mmapfiles N
start N workers that attempt to memory map and then unmap up to 512 × 1024
files into memory. The stressor will traverse /lib, /lib32, /lib64, /boot,
/bin, /etc, /sbin, /usr, /var, /sys and /proc and attempt to memory map files
in these directories. Note that mapping bogo-ops rate will depend on the speed
of access to files on these file systems.

--mmapfiles-ops N
stop after N memory map/unmap operations.

--mmapfiles-populate
The default is to perform a memory mapping and not fault any pages into
physical memory. This option uses MAP_POPULATE when available and will also
read the first byte in each page to ensure pages are faulted into memory to
force memory population from file.

--mmapfiles-shared
The default is for private memory mapped files, however, with this option will
use shared memory mappings.

Fixed address memory map stressor
--mmapfixed N
start N workers that perform fixed address allocations from the top virtual
address down to 128K. The allocated sizes are from 1 page to 8 pages and
various random mmap flags are used MAP_SHARED/MAP_PRIVATE, MAP_LOCKED,
MAP_NORESERVE, MAP_POPULATE. If successfully map'd then the allocation is
remap'd first to a large range of addresses based on a random start and
finally an address that is several pages higher in memory. Mappings and
remappings are madvised with random madvise options to further exercise the
mappings.

--mmapfixed-mlock
attempt to mlock mmap'd pages into memory causing more memory pressure by
preventing pages from swapped out.

--mmapfixed-ops N
stop after N mmapfixed memory mapping bogo operations.

Huge page memory mapping stressor
--mmaphuge N
start N workers that attempt to mmap a set of huge pages and large huge page
sized mappings. Successful mappings are madvised with MADV_NOHUGEPAGE and
MADV_HUGEPAGE settings and then 1/64th of the normal small page size pages are
touched. Finally, an attempt to unmap a small page size page at the end of the
mapping is made (these may fail on huge pages) before the set of pages are
unmapped. By default 8192 mappings are attempted per round of mappings or
until swapping is detected.

--mmaphuge-file
attempt to mmap on a 16MB temporary file and random 4K offsets. If this fails,
anonymous mappings are used instead.

--mmaphuge-mlock
attempt to mlock mmap'd huge pages into memory causing more memory pressure by
preventing pages from swapped out.

--mmaphuge-mmaps N
set the number of huge page mappings to attempt in each round of mappings. The
default is 8192 mappings.

--mmaphuge-ops N
stop after N mmaphuge bogo operations

Maximum memory mapping per process stressor
--mmapmany N
start N workers that attempt to create the maximum allowed per-process memory
mappings. This is achieved by mapping 3 contiguous pages and then unmapping
the middle page hence splitting the mapping into two. This is then repeated
until the maximum allowed mappings or a maximum of 262144 mappings are made.

--mmapmany-mlock
attempt to mlock mmap'd huge pages into memory causing more memory pressure by
preventing pages from swapped out.

--mmapmany-ops N
stop after N mmapmany bogo operations

Kernel module loading stressor (Linux)
--module N
start N workers that use finit_module() to load the module specified or the
hello test module, if is available. There are different ways to test loading
modules. Using modprobe calls in a loop, using the kernel kernel module
autoloader, and this stress-ng module stressor. To stress tests modprobe we
can simply run the userspace modprobe program in a loop. To stress test the
kernel module autoloader we can stress tests using the upstream kernel
tools/testing/selftests/kmod/kmod.sh. This ends up calling modprobe in the
end, and it has its own caps built-in to self protect the kernel from too many
requests at the same time. The userspace modprobe call will also prevent calls
if the same module exists already. The stress-ng modules stressor is designed
to help stress test the finit_module() system call even if the module is
already loaded, testing races that are otherwise hard to reproduce.

--module-name NAME
NAME of the module to use, for example: test_module, xfs, ext4. By default
test_module is used so CONFIG_TEST_LKM must be enabled in the kernel. The
module dependencies must be loaded prior to running these stressor tests, as
this stresses running finit_module() not using modprobe.

--module-no-modver
ignore module modversions when using finit_module().

--module-no-vermag
ignore module versions when using finit_module().

--module-no-unload
do not unload the module right after loading it with finit_module().

--module-ops N
stop after N module load/unload cycles

Monte Carlo computations of π and e and various integrals
--monte-carlo N
start N stressors that compute π and e (Euler's number) using Monte Carlo
computational experiments with various random number generators.

--monte-carlo-method [ all | e | exp | pi | sin | sqrt ]
specify the computation to perform, options are as follows:

Method Description
all use all monte carlo computation methods
e compute Euler's constant e
exp integrate exp(x ↑ 2) for x = 0..1
pi compute π from the area of a circle
sin integrate sin(x) for x = 0..π
sqrt integrate sqrt(1 + x ↑ 4) for x = 0..1

--monte-carlo-ops N
stop after Monte Carlo computation experiments

Method Description
all use all the random number generators
arc4 use the libc cryptographically-secure pseudorandom arc4random(3)
number generator.
drand48 use the libc linear congruential algorithm drand48(3) using 48-bit
integer arithmetic.
getrandom use the getrandom(2) system call for random values.
lcg use a 32 bit Paker-Miller Linear Congruential Generator, with a
division optimization.
pcg32 use a 32 bit O'Neill Permuted Congruential Generator.
mwc64 use the 64 bit stress-ng Multiply With Carry random number
generator.
random use the libc random(3) Non-linear Additive Feedback random number
generator.
xorshift use a 32 bit Marsaglia shift-register random number generator.

--monte-carlo-samples N
specify the number of random number samples to use to compute π or e, default
is 100000.

Multi-precision floating operations (mpfr) stressor
--mpfr N
start N workers that exercise multi-precision floating point operations using
the GNU Multi-Precision Floating Point Reliable library (mpfr). Operations
computed are as follows:

Method Description
apery calculate Apery's constant ζ(3); the sum of 1/(n ↑ 3).
cosine compute cos(θ) for θ = 0 to 2π in 100 steps.
euler compute e using n = (1 + (1 ÷ n)) ↑ n.
exp compute 1000 exponentials.
log computer 1000 natural logarithms.
omega compute the omega constant defined by Ωe↑Ω = 1 using efficient
iteration of Ωn+1 = (1 + Ωn) / (1 + e↑Ωn).
phi compute the Golden Ratio ϕ using series.
sine compute sin(θ) for θ = 0 to 2π in 100 steps.
nsqrt compute square root using Newton-Raphson.

--mpfr-ops N
stop workers after N iterations of various multi-precision floating point
operations.

--mpfr-precision N
specify the precision in binary digits of the floating point operations. The
default is 1000 bits, the allowed range is 32 to 1000000 (very slow).

Memory protection stressor
--mprotect N
start N workers that exercise changing page protection settings and access
memory after each change. 8 processes per worker contend with each other
changing page proection settings on a shared memory region of just a few pages
to cause TLB flushes. A read and write to the pages can cause segmentation
faults and these are handled by the stressor. All combinations of page
protection settings are exercised including invalid combinations.

--mprotect-ops N
stop after N mprotect calls.

POSIX message queue stressor (Linux)
--mq N start N sender and receiver processes that continually send and receive
messages using POSIX message queues. (Linux only).

--mq-ops N
stop after N bogo POSIX message send operations completed.

--mq-size N
specify size of POSIX message queue. The default size is 10 messages and most
Linux systems this is the maximum allowed size for normal users. If the given
size is greater than the allowed message queue size then a warning is issued
and the maximum allowed size is used instead.

Memory remap stressor (Linux)
--mremap N
start N workers continuously calling mmap(2), mremap(2) and munmap(2). The
initial anonymous mapping is a large chunk (size specified by --mremap-bytes)
and then iteratively halved in size by remapping all the way down to a page
size and then back up to the original size. This worker is only available for
Linux.

--mremap-bytes N
initially allocate N bytes per remap stress worker, the default is 256MB. One
can specify the size in units of Bytes, KBytes, MBytes and GBytes using the
suffix b, k, m or g.

--mremap-mlock
attempt to mlock remap'd pages into memory causing more memory pressure by
preventing pages from swapped out.

--mremap-ops N
stop mremap stress workers after N bogo operations.

System V message IPC stressor
--msg N
start N sender and receiver processes that continually send and receive
messages using System V message IPC.

--msg-bytes N
specify the size of the message being sent and received. Range 4 to 8192
bytes, default is 4 bytes.

--msg-ops N
stop after N bogo message send operations completed.

--msg-types N
select the quality of message types (mtype) to use. By default, msgsnd sends
messages with a mtype of 1, this option allows one to send messages types in
the range 1..N to exercise the message queue receive ordering. This will also
impact throughput performance.

Synchronize file with memory map (msync) stressor
--msync N
start N stressors that msync data from a file backed memory mapping from
memory back to the file and msync modified data from the file back to the
mapped memory. This exercises the msync(2) MS_SYNC and MS_INVALIDATE sync
operations.

--msync-bytes N
allocate N bytes for the memory mapped file, the default is 256MB. One can
specify the size as % of total available memory or in units of Bytes, KBytes,
MBytes and GBytes using the suffix b, k, m or g.

--msync-ops N
stop after N msync bogo operations completed.

Synchronize file with memory map (msync) coherency stressor
--msyncmany N
start N stressors that memory map up to 32768 pages on the same page of a
temporary file, change the first 32 bits in a page and msync the data back to
the file. The other 32767 pages are examined to see if the 32 bit check value
is msync'd back to these pages.

--msyncmany-ops N
stop after N msync calls in the msyncmany stressors are completed.

Unmapping shared non-executable memory stressor (Linux)
--munmap N
start N stressors that exercise unmapping of shared non-executable mapped
regions of child processes (Linux only). The unmappings map shared memory
regions page by page with a prime sized stride that creates many temporary
mapping holes. One the unmappings are complete the child will exit and a new
one is started. Note that this may trigger segmentation faults in the child
process, these are handled where possible by forcing the child process to call
_exit(2).

--munmap-ops N
stop after N page unmappings.

Pthread mutex stressor
--mutex N
start N stressors that exercise pthread mutex locking and unlocking. If run
with enough privilege then the FIFO scheduler is used and a random priority
between 0 and 80% of the maximum FIFO priority level is selected for the
locking operation. The minimum FIFO priority level is selected for the
critical mutex section and unlocking operation to exercise random inverted
priority scheduling.

--mutex-affinity
enable random CPU affinity changing between mutex lock and unlock.

--mutex-ops N
stop after N bogo mutex lock/unlock operations.

--mutex-procs N
By default 2 threads are used for locking/unlocking on a single mutex. This
option allows the default to be changed to 2 to 64 concurrent threads.

High resolution and scheduler stressor via nanosleep calls
--nanosleep N
start N workers that each run pthreads that call nanosleep with random delays
from 1 to 2↑18 nanoseconds. This should exercise the high resolution timers
and scheduler.

Method Description
all use cstate and random nanosecond durations.
cstate use cstate nanosecond durations. It is recommended to also use
--nanosleep-threads 1 to exercise less conconcurrent nanosleeps to
allow CPUs to drop into deep C states.
random use random nanosecond durations between 1 and 2^18 nanoseconds.
ns use 1ns (nanosecond) nanosleeps
us use 1us (microsecond) nanosleeps
ms use 1ms (millisecond) nanosleeps

--nanosleep-ops N
stop the nanosleep stressor after N bogo nanosleep operations.

--nanosleep-threads N
specify the number of concurrent pthreads to run per stressor. The default is
8 and the allowed range is 1 to 1024.

Network device ioctl stressor
--netdev N
start N workers that exercise various netdevice ioctl commands across all the
available network devices. The ioctls exercised by this stressor are as
follows: SIOCGIFCONF, SIOCGIFINDEX, SIOCGIFNAME, SIOCGIFFLAGS, SIOCGIFADDR,
SIOCGIFNETMASK, SIOCGIFMETRIC, SIOCGIFMTU, SIOCGIFHWADDR, SIOCGIFMAP and
SIOCGIFTXQLEN. See netdevice(7) for more details of these ioctl commands.

--netdev-ops N
stop after N netdev bogo operations completed.

Netlink stressor (Linux)
--netlink-proc N
start N workers that spawn child processes and monitor fork/exec/exit process
events via the proc netlink connector. Each event received is counted as a
bogo op. This stressor can only be run on Linux and requires CAP_NET_ADMIN
capability.

--netlink-proc-ops N
stop the proc netlink connector stressors after N bogo ops.

--netlink-task N
start N workers that collect task statistics via the netlink taskstats
interface. This stressor can only be run on Linux and requires CAP_NET_ADMIN
capability.

--netlink-task-ops N
stop the taskstats netlink connector stressors after N bogo ops.

Nice stressor
--nice N
start N cpu consuming workers that exercise the available nice levels. Each
iteration forks off a child process that runs through the all the nice levels
running a busy loop for 0.1 seconds per level and then exits.

--nice-ops N
stop after N nice bogo nice loops

NO-OP CPU instruction stressor
--nop N
start N workers that consume cpu cycles issuing no-op instructions. This
stressor is available if the assembler supports the "nop" instruction.

--nop-instr INSTR
use alternative nop instruction INSTR. For x86 CPUs INSTR can be one of nop,
pause, nop2 (2 byte nop) through to nop15 (15 byte nop). For ARM CPUs, INSTR
can be one of nop or yield. For PPC64 CPUs, INSTR can be one of nop, mdoio,
mdoom or yield. For S390 CPUs, INSTR can be one of nop or nopr. For other
processors, INSTR is only nop. The random INSTR option selects a randon mix of
the available nop instructions. If the chosen INSTR generates an SIGILL
signal, then the stressor falls back to the vanilla nop instruction.

--nop-ops N
stop nop workers after N no-op bogo operations. Each bogo-operation is
equivalent to 256 loops of 256 no-op instructions.

/dev/null stressor
--null N
start N workers that exercise /dev/null with writes, lseek, ioctl, fcntl,
fallocate and fdatasync. For just /dev/null write benchmarking use the
--null-write option.

--null-ops N
stop null stress workers after N /dev/null bogo operations.

--null-write
just write to /dev/null with 4K writes with no additional exercising on
/dev/null.

Migrate memory pages over NUMA nodes stressor
--numa N
start N workers that migrate stressors and a 4MB memory mapped buffer around
all the available NUMA nodes. This uses migrate_pages(2) to move the
stressors and mbind(2) and move_pages(2) to move the pages of the mapped
buffer. After each move, the buffer is written to force activity over the bus
which results cache misses. This test will only run on hardware with NUMA
enabled and more than 1 NUMA node.

--numa-bytes N
specify the total number bytes to be exercised by all the workers, the given
size is divided by the number of workers and rounded to the nearest page size.
The default is 4MB per worker. One can specify the size as % of total
available memory or in units of Bytes, KBytes, MBytes and GBytes using the
suffix b, k, m or g.

--numa-ops N
stop NUMA stress workers after N bogo NUMA operations.

--numa-shuffle-addr
shuffle page order for the address list when calling move_pages(2)

--numa-shuffle-node
shuffle node order for the address list when calling move_pages(2)

Large Pipe stressor
--oom-pipe N
start N workers that create as many pipes as allowed and exercise expanding
and shrinking the pipes from the largest pipe size down to a page size. Data
is written into the pipes and read out again to fill the pipe buffers. With
the --aggressive mode enabled the data is not read out when the pipes are
shrunk, causing the kernel to OOM processes aggressively. Running many
instances of this stressor will force kernel to OOM processes due to the many
large pipe buffer allocations.

--oom-pipe-ops N
stop after N bogo pipe expand/shrink operations.

Illegal instructions stressors
--opcode N
start N workers that fork off children that execute randomly generated
executable code. This will generate issues such as illegal instructions, bus
errors, segmentation faults, traps, floating point errors that are handled
gracefully by the stressor.

--opcode-method [ inc | mixed | random | text ]
select the opcode generation method. By default, random bytes are used to
generate the executable code. This option allows one to select one of the
three methods:

Method Description
inc use incrementing 32 bit opcode patterns from 0x00000000 to 0xfffffff
inclusive.
mixed use a mix of incrementing 32 bit opcode patterns and random 32 bit
opcode patterns that are also inverted, encoded with gray encoding and
bit reversed.
random generate opcodes using random bytes from a mwc random generator.
text copies random chunks of code from the stress-ng text segment and
randomly flips single bits in a random choice of 1/8th of the code.

--opcode-ops N
stop after N attempts to execute illegal code.

Opening file (open) stressor
-o N, --open N
start N workers that perform open(2) and then close(2) operations on
/dev/zero. The maximum opens at one time is system defined, so the test will
run up to this maximum, or 65536 open file descriptors, which ever comes
first.

--open-fd
run a child process that scans /proc/$PID/fd and attempts to open the files
that the stressor has opened. This exercises racing open/close operations on
the proc interface.

--open-max N
try to open a maximum of N files (or up to the maximum per-process open file
system limit). The value can be the number of files or a percentage of the
maximum per-process open file system limit.

--open-ops N
stop the open stress workers after N bogo open operations.

Page table and TLB stressor
--pagemove N
start N workers that mmap a memory region (default 4 MB) and then shuffle
pages to the virtual address of the previous page. Each page shuffle uses 3
mremap operations to move a page. This exercises page tables and Translation
Lookaside Buffer (TLB) flushing.

--pagemove-bytes
specify the size of the memory mapped region to be exercised. One can specify
the size as % of total available memory or in units of Bytes, KBytes, MBytes
and GBytes using the suffix b, k, m or g.

--pagemove-mlock
attempt to mlock mmap'd and mremap'd pages into memory causing more memory
pressure by preventing pages from swapped out.

--pagemove-ops N
stop after N pagemove shuffling operations, where suffling all the pages in
the mmap'd region is equivalent to 1 bogo-operation.

Memory page swapping stressor
--pageswap N
start N workers that exercise page swap in and swap out. Pages are allocated
and paged out using madvise MADV_PAGEOUT. One the maximum per process number
of mmaps are reached or 65536 pages are allocated the pages are read to page
them back in and unmapped in reverse mapping order.

--pageswap-ops N
stop after N page allocation bogo operations.

PCI sysfs stressor (Linux)
--pci N
exercise PCI sysfs by running N workers that read data (and mmap/unmap PCI
config or PCI resource files). Linux only. Running as root will allow config
and resource mmappings to be read and exercises PCI I/O mapping.

--pci-ops N
stop pci stress workers after N PCI subdirectory exercising operations.

Personality stressor
--personality N
start N workers that attempt to set personality and get all the available
personality types (process execution domain types) via the personality(2)
system call. (Linux only).

--personality-ops N
stop personality stress workers after N bogo personality operations.

Mutex using Peterson algorithm stressor
--peterson N
start N workers that exercises mutex exclusion between two processes using
shared memory with the Peterson Algorithm. Where possible this uses memory
fencing and falls back to using GCC __sync_synchronize if they are not
available. The stressors contain simple mutex and memory coherency sanity
checks.

--peterson-ops N
stop peterson workers after N mutex operations.

Page map stressor
--physpage N
start N workers that use /proc/self/pagemap and /proc/kpagecount to determine
the physical page and page count of a virtual mapped page and a page that is
shared among all the stressors. Linux only and requires the CAP_SYS_ADMIN
capabilities.

--physpage-mtrr
enable setting various memory type rage register (MTRR) types on physical
pages (Linux and x86 only).

--physpage-ops N
stop physpage stress workers after N bogo physical address lookups.

Process signals (pidfd_send_signal) stressor
--pidfd N
start N workers that exercise signal sending via the pidfd_send_signal system
call. This stressor creates child processes and checks if they exist and can
be stopped, restarted and killed using the pidfd_send_signal system call.

--pidfd-ops N
stop pidfd stress workers after N child processes have been created, tested
and killed with pidfd_send_signal.

Localhost ICMP (ping) stressor
--ping-sock N
start N workers that send small randomized ICMP messages to the localhost
across a range of ports (1024..65535) using a "ping" socket with an AF_INET
domain, a SOCK_DGRAM socket type and an IPPROTO_ICMP protocol.

--ping-sock-ops N
stop the ping-sock stress workers after N ICMP messages are sent.

Large pipe stressor
-p N, --pipe N
start N workers that perform large pipe writes and reads to exercise pipe I/O.
This exercises memory write and reads as well as context switching. Each
worker has two processes, a reader and a writer.

--pipe-data-size N
specifies the size in bytes of each write to the pipe (range from 4 bytes to
4096 bytes). Setting a small data size will cause more writes to be buffered
in the pipe, hence reducing the context switch rate between the pipe writer
and pipe reader processes. Default size is the page size.

--pipe-ops N
stop pipe stress workers after N bogo pipe write operations.

--pipe-vmsplice
use vmsplice(2) to splice data pages to/from pipe. Requires pipe packet mode
using O_DIRECT and buffer twice the size of the pipe to ensure verification
data sequences.

--pipe-size N
specifies the size of the pipe in bytes (for systems that support the
F_SETPIPE_SZ fcntl() command). Setting a small pipe size will cause the pipe
to fill and block more frequently, hence increasing the context switch rate
between the pipe writer and the pipe reader processes. As of version 0.15.11
the default size is 4096 bytes.

Shared pipe stressor
--pipeherd N
start N workers that pass a 64 bit token counter to/from 100 child processes
over a shared pipe. This forces a high context switch rate and can trigger a
"thundering herd" of wakeups on processes that are blocked on pipe waits.

--pipeherd-ops N
stop pipe stress workers after N bogo pipe write operations.

--pipeherd-yield
force a scheduling yield after each write, this increases the context switch
rate.

Memory protection key mechanism stressor (Linux)
--pkey N
start N workers that change memory protection using a protection key (pkey)
and the pkey_mprotect call (Linux only). This will try to allocate a pkey and
use this for the page protection, however, if this fails then the special pkey
-1 will be used (and the kernel will use the normal mprotect mechanism
instead). Various page protection mixes of read/write/exec/none will be
cycled through on randomly chosen pre-allocated pages.

--pkey-ops N
stop after N pkey_mprotect page protection cycles.

Stress-ng plugin stressor
--plugin N
start N workers that run user provided stressor functions loaded from a shared
library. The shared library can contain one or more stressor functions
prefixed with stress_ in their name. By default the plugin stressor will find
all functions prefixed with stress_ in their name and exercise these one by
one in a round-robin loop, but a specific stressor can be selected using the
--plugin-method option. The stressor function takes no parameters and returns
0 for success and non-zero for failure (and will terminate the plugin
stressor). Each time a stressor function is executed the bogo-op counter is
incremented by one. The following example performs 10,000 nop instructions per
bogo-op:

int stress_example(void)
{
int i;

for (i = 0; i < 10000; i++) {
__volatile__ __asm__("nop");
}
return 0; /* Success */
}

and compile the source into a shared library as, for example:

gcc -fpic -shared -o example.so example.c

and run as using:

stress-ng --plugin 1 --plugin-so ./example.so

--plugin-method function
run a specific stressor function, specify the name without the leading stress_
prefix.

--plugin-ops N
stop after N iterations of the user provided stressor function(s).

--plugin-so name
specify the shared library containing the user provided stressor function(s).

Polling stressor
-P N, --poll N
start N workers that perform zero timeout polling via the poll(2), ppoll(2),
select(2), pselect(2) and sleep(3) calls. This wastes system and user time
doing nothing.

--poll-fds N
specify the number of file descriptors to poll/ppoll/select/pselect on. The
maximum number for select/pselect is limited by FD_SETSIZE and the upper
maximum is also limited by the maximum number of pipe open descriptors
allowed.

--poll-ops N
stop poll stress workers after N bogo poll operations.

Prctl stressor
--prctl N
start N workers that exercise the majority of the prctl(2) system call
options. Each batch of prctl calls is performed inside a new child process to
ensure the limit of prctl is contained inside a new process every time. Some
prctl options are architecture specific, however, this stressor will exercise
these even if they are not implemented.

--prctl-ops N
stop prctl workers after N batches of prctl calls

L3 cache prefetching stressor
--prefetch N
start N workers that benchmark prefetch and non-prefetch reads of a L3 cache
sized buffer. The buffer is read with loops of 8 × 64 bit reads per iteration.
In the prefetch cases, data is prefetched ahead of the current read position
by various sized offsets, from 64 bytes to 8K to find the best memory read
throughput. The stressor reports the non-prefetch read rate and the best
prefetched read rate. It also reports the prefetch offset and an estimate of
the amount of time between the prefetch issue and the actual memory read
operation. These statistics will vary from run-to-run due to system noise and
CPU frequency scaling.

--prefetch-l3-size N
specify the size of the l3 cache

--prefetch-method N
select the prefetching method. Available methods are:

Method Description
builtin Use the __builtin_prefetch(3) function for prefetching. This is
the default.
builtinl0 Use the __builtin_prefetch(3) function for prefetching, with a
locality 0 hint.
builtinl3 Use the __builtin_prefetch(3) function for prefetching, with a
locality 3 hint.
dcbt Use the ppc64 dcbt instruction to fetch data into the L1 cache
(ppc64 only).
dcbtst Use the ppc64 dcbtst instruction to fetch data into the L1 cache
(ppc64 only).
prefetcht0 Use the x86 prefetcht0 instruction to prefetch data into all
levels of the cache hierarchy (x86 only).
prefetcht1 Use the x86 prefetcht1 instruction (temporal data with respect to
first level cache) to prefetch data into level 2 cache and higher
(x86 only).
prefetcht2 Use the x86 prefetcht2 instruction (temporal data with respect to
second level cache) to prefetch data into level 2 cache and
higher (x86 only).
prefetchnta Use the x86 prefetchnta instruction (non-temporal data with
respect to all cache levels) into a location close to the
processor, minimizing cache pollution (x86 only).

--prefetch-ops N
stop prefetch stressors after N benchmark operations

Priority inversion stressor
--prio-inv N
start N workers that exercise mutex lock priority inversion scheduling. Three
child process run with low, medium and high FIFO scheduling priorities. The
processes with low and high priorities share a mutex lock that both try to
lock and unlock, aiming to make the low priority process block the high
priority process. Meanwhile the middle priority process will run in priority
over the low priority process, causing the high priority process to become
unrunnable.

--prio-inv-ops N
stop after N bogo lock/unlock operations.

--prio-inv-type [ inherit | none | protect ]
select the mutex lock priority inversion type, described as follows:

Type Description
inherit The priority of the process owning the mutex lock is run with highest
priority of any other process waiting on the lock to avoid priority
inversion deadlock.
none The priority of the process owning the mutex lock is not affected by
its mutex ownership. This may lead to the high priority process to
become unrunnable on a single thread system.
protect The priority of the process owning the mutex lock is given the
priority of the mutex (in this stress test case, the maximum
priority) during the lock ownership.

--prio-inv-policy [ batch, idle, fifo, other, rr ]
select the scheduling policy. "Normal" policies (batch, idle and other) can be
selected as an unprivileged user, however "Real Time" policies (fifo and rr)
can only be selected with the appropriate privilege. By default "rr" is
selected but will it fall back to "other" for unprivileged users.

Privileged CPU instructions stressor
--priv-instr N
start N workers that exercise various architecture specific privileged
instructions that cannot be executed by userspace programs. These instructions
will be trapped and processed by SIGSEGV or SIGILL signal handlers.

--priv-instr-ops N
stop priv-instr stressors after N rounds of executing privileged instructions.

/proc stressor
--procfs N
start N workers that read files from /proc and recursively read files from
/proc/self (Linux only).

--procfs-ops N
stop procfs reading after N bogo read operations. Note, since the number of
entries may vary between kernels, this bogo ops metric is probably very
misleading.

Pthread stressor
--pthread N
start N workers that iteratively creates and terminates multiple pthreads (the
default is 1024 pthreads per worker). In each iteration, each newly created
pthread waits until the worker has created all the pthreads and then they all
terminate together.

--pthread-max N
create N pthreads per worker. If the product of the number of pthreads by the
number of workers is greater than the soft limit of allowed pthreads then the
maximum is re-adjusted down to the maximum allowed.

--pthread-ops N
stop pthread workers after N bogo pthread create operations.

Ptrace stressor
--ptrace N
start N workers that fork and trace system calls of a child process using
ptrace(2).

--ptrace-ops N
stop ptracer workers after N bogo system calls are traced.

Pseudo-terminals (pty) stressor
--pty N
start N workers that repeatedly attempt to open pseudoterminals and perform
various pty ioctls upon the ptys before closing them.

--pty-max N
try to open a maximum of N pseudoterminals, the default is 65536. The allowed
range of this setting is 8..65536.

--pty-ops N
stop pty workers after N pty bogo operations.

Qsort stressor
-Q, --qsort N
start N workers that sort 32 bit integers using qsort.

--qsort-method [ qsort-libc | qsort-bm ]
select either the libc implementation of qsort or the J. L. Bentley and M. D.
McIlroy implementation of qsort. The default is the libc implementation.

--qsort-ops N
stop qsort stress workers after N bogo qsorts.

--qsort-size N
specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

Quota stressor
--quota N
start N workers that exercise the Q_GETQUOTA, Q_GETFMT, Q_GETINFO, Q_GETSTATS
and Q_SYNC quotactl(2) commands on all the available mounted block based file
systems. Requires CAP_SYS_ADMIN capability to run.

--quota-ops N
stop quota stress workers after N bogo quotactl operations.

Process scheduler stressor
--race-sched N
start N workers that exercise rapid changing CPU affinity child processes both
from the controlling stressor and by the child processes. Child processes are
created and terminated rapidly with the aim to create race conditions where
affinity changing occurs during process run states.

Method Description
all iterate over all the race-sched methods as listed below:
next move a process to the next CPU, wrap around to zero when maximum CPU
is reached.
prev move a process to the previous CPU, wrap around to the maximum CPU
when the first CPU is reached.
rand move a process to any randomly chosen CPU.
randinc move a process to the current CPU + a randomly chosen value 1..4,
modulo the number of CPUs.
syncnext move synchronously all the race-sched stressor processes to the next
CPU every second; this loads just 1 CPU at a time in a round-robin
method.
syncprev move synchronously all the race-sched stressor processes to the
previous CPU every second; this loads just 1 CPU at a time in a
round-robin method.

--race-sched-ops N
stop after N process creation bogo-operations.

Radixsort stressor
--radixsort N
start N workers that sort random 8 byte strings using radixsort.

--radixsort-method [ radixsort-libc | radixsort-nonlibc ]
select either the libc implementation of radixsort or an optimized
implementation of radixsort. The default is the libc implementation if it is
available.

--radixsort-ops N
stop radixsort stress workers after N bogo radixsorts.

--radixsort-size N
specify number of strings to sort, default is 262144 (256 × 1024).

Memory filesystem stressor
--ramfs N
start N workers mounting a memory based file system using ramfs and tmpfs
(Linux only). This alternates between mounting and umounting a ramfs or tmpfs
file system using the traditional mount(2) and umount(2) system call as well
as the newer Linux 5.2 fsopen(2), fsmount(2), fsconfig(2) and move_mount(2)
system calls if they are available. The default ram file system size is 2MB.

--ramfs-fill
fill ramfs with zero'd data using fallocate(2) if it is available or multiple
calls to write(2) if not.

--ramfs-ops N
stop after N ramfs mount operations.

--ramfs-size N
set the ramfs size (must be multiples of the page size).

Raw device stressor
--rawdev N
start N workers that read the underlying raw drive device using direct IO
reads. The device (with minor number 0) that stores the current working
directory is the raw device to be read by the stressor. The read size is
exactly the size of the underlying device block size. By default, this
stressor will exercise all the of the rawdev methods (see the --rawdev-method
option). This is a Linux only stressor and requires root privilege to be able
to read the raw device.

--rawdev-method method
Available rawdev stress methods are described as follows:

Method Description
all iterate over all the rawdev stress methods as listed below:
sweep repeatedly read across the raw device from the 0th block to the end
block in steps of the number of blocks on the device / 128 and back to
the start again.
wiggle repeatedly read across the raw device in 128 evenly steps with each
step reading 1024 blocks backwards from each step.
ends repeatedly read the first and last 128 start and end blocks of the raw
device alternating from start of the device to the end of the device.
random repeatedly read 256 random blocks
burst repeatedly read 256 sequential blocks starting from a random block on
the raw device.

--rawdev-ops N
stop the rawdev stress workers after N raw device read bogo operations.

Random list stressor
--randlist N
start N workers that creates a list of objects in randomized memory order and
traverses the list setting and reading the objects. This is designed to
exerise memory and cache thrashing. Normally the objects are allocated on the
heap, however for objects of page size or larger there is a 1 in 16 chance of
objects being allocated using shared anonymous memory mapping to mix up the
address spaces of the allocations to create more TLB thrashing.

--randist-compact
Allocate all the list objects using one large heap allocation and divide this
up for all the list objects. This removes the overhead of the heap keeping
track of each list object, hence uses less memory.

--randlist-items N
Allocate N items on the list. By default, 100,000 items are allocated.

--randlist-ops N
stop randlist workers after N list traversals

--randlist-size N
Allocate each item to be N bytes in size. By default, the size is 64 bytes of
data payload plus the list handling pointer overhead.

Localhost raw socket stressor
--rawsock N
start N workers that send and receive packet data using raw sockets on the
localhost. Requires CAP_NET_RAW to run.

--rawsock-ops N
stop rawsock workers after N packets are received.

--rawsock-port P
start at socket port P. For N rawsock worker processes, ports P to P - 1 are
used.

Localhost ethernet raw packets stressor
--rawpkt N
start N workers that sends and receives ethernet packets using raw packets on
the localhost via the loopback device. Requires CAP_NET_RAW to run.

--rawpkt-ops N
stop rawpkt workers after N packets from the sender process are received.

--rawpkt-port N
start at port P. For N rawpkt worker processes, ports P to (P * 4) - 1 are
used. The default starting port is port 14000.

--rawpkt-rxring N
setup raw packets with RX ring with N number of blocks, this selects
TPACKET_V. N must be one of 1, 2, 4, 8 or 16.

Localhost raw UDP packet stressor
--rawudp N
start N workers that send and receive UDP packets using raw sockets on the
localhost. Requires CAP_NET_RAW to run.

--rawudp-if NAME
use network interface NAME. If the interface NAME does not exist, is not up or
does not support the domain then the loopback (lo) interface is used as the
default.

--rawudp-ops N
stop rawudp workers after N packets are received.

--rawudp-port N
start at port P. For N rawudp worker processes, ports P to (P * 4) - 1 are
used. The default starting port is port 13000.

Random number generator stressor
--rdrand N
start N workers that read a random number from an on-chip random number
generator This uses the rdrand instruction on Intel x86 processors or the darn
instruction on Power9 processors.

--rdrand-ops N
stop rdrand stress workers after N bogo rdrand operations (1 bogo op = 2048
random bits successfully read).

--rdrand-seed
use rdseed instead of rdrand (x86 only).

Read-ahead stressor
--readahead N
start N workers that randomly seek and perform 4096 byte read/write I/O
operations on a file with readahead. The default file size is 64 MB.
Readaheads and reads are batched into 16 readaheads and then 16 reads.

--readahead-bytes N
set the size of readahead file, the default is 1 GB. One can specify the size
as % of free space on the file system or in units of Bytes, KBytes, MBytes and
GBytes using the suffix b, k, m or g.

--readahead-ops N
stop readahead stress workers after N bogo read operations.

Reboot stressor
--reboot N
start N workers that exercise the reboot(2) system call. When possible, it
will create a process in a PID namespace and perform a reboot power off
command that should shutdown the process. Also, the stressor exercises
invalid reboot magic values and invalid reboots when there are insufficient
privileges that will not actually reboot the system.

--reboot-ops N
stop the reboot stress workers after N bogo reboot cycles.

CPU registers stressor
--regs N
start N workers that shuffle data around the CPU registers exercising register
move instructions. Each bogo-op represents 1000 calls of a shuffling function
that shuffles the registers 32 times. Only implemented for the GCC compiler
since this requires register annotations and optimization level 0 to compile
appropriately.

--regs-ops N
stop regs stressors after N bogo operations.

Memory page reordering stressor
--remap N
start N workers that map 512 pages and re-order these pages using the
deprecated system call remap_file_pages(2). Several page re-orderings are
exercised: forward, reverse, random and many pages to 1 page.

--remap-mlock
attempt to mlock mmap'd huge pages into memory causing more memory pressure by
preventing pages from swapped out.

--remap-ops N
stop after N remapping bogo operations.

--remap-pages N
specify number of pages to remap, must be a power of 2, default is 512 pages.

Renaming file stressor
-R N, --rename N
start N workers that each create a file and then repeatedly rename it.

--rename-ops N
stop rename stress workers after N bogo rename operations.

Process rescheduling stressor
--resched N
start N workers that exercise process rescheduling. Each stressor spawns a
child process for each of the positive nice levels and iterates over the nice
levels from 0 to the lowest priority level (highest nice value). For each of
the nice levels 1024 iterations over 3 non-real time scheduling polices
SCHED_OTHER, SCHED_BATCH and SCHED_IDLE are set and a sched_yield occurs to
force heavy rescheduling activity. When the -v verbose option is used the
distribution of the number of yields across the nice levels is printed for the
first stressor out of the N stressors.

--resched-ops N
stop after N rescheduling sched_yield calls.

System resources stressor
--resources N
start N workers that consume various system resources. Each worker will spawn
1024 child processes that iterate 1024 times consuming shared memory, heap,
stack, temporary files and various file descriptors (eventfds, memoryfds,
userfaultfds, pipes and sockets).

--resources-mlock
attempt to mlock mmap'd pages into memory causing more memory pressure by
preventing pages from swapped out.

--resources-ops N
stop after N resource child forks.

Writing temporary files in reverse position stressor
--revio N
start N workers continually writing in reverse position order to temporary
files. The default mode is to stress test reverse position ordered writes with
randomly sized sparse holes between each write. With the --aggressive option
enabled without any --revio-opts options the revio stressor will work through
all the --revio-opt options one by one to cover a range of I/O options.

--revio-bytes N
write N bytes for each revio process, the default is 1 GB. One can specify the
size as % of free space on the file system or in units of Bytes, KBytes,
MBytes and GBytes using the suffix b, k, m or g.

--revio-opts list
specify various stress test options as a comma separated list. Options are the
same as --hdd-opts but without the iovec option.

--revio-ops N
stop revio stress workers after N bogo operations.

--revio-write-size N
specify size of each write in bytes. Size can be from 1 byte to 4MB.

Ring pipes stressor
--ring-pipe N
start N workers that move data around a ring of pipes using poll to detect
when data is ready to copy. By default, 256 pipes are used with two 4096 byte
items of data being copied around the ring of pipes. Data is copied using read
and write system calls. If the splice system call is available then one can
use splice to use more efficient in-kernel data passing instead of buffer
copying.

--ring-pipe-num N
specify the number of pipes to use. Ranges from 4 to 262144, default is 256.

--ring-pipe-ops N
stop after N pipe data transfers.

--ring-pipe-size N
specify the size of data being copied in bytes. Ranges from 1 to 4096, default
is 4096.

--ring-pipe-splice
enable splice to move data between pipes (only if splice() is available).

Rlimit stressor
--rlimit N
start N workers that exceed CPU and file size resource imits, generating
SIGXCPU and SIGXFSZ signals.

--rlimit-ops N
stop after N bogo resource limited SIGXCPU and SIGXFSZ signals have been
caught.

VM reverse-mapping stressor
--rmap N
start N workers that exercise the VM reverse-mapping. This creates 16
processes per worker that write/read multiple file-backed memory mappings.
There are 64 lots of 4 page mappings made onto the file, with each mapping
overlapping the previous by 3 pages and at least 1 page of non-mapped memory
between each of the mappings. Data is synchronously msync'd to the file 1 in
every 256 iterations in a random manner.

--rmap-ops N
stop after N bogo rmap memory writes/reads.

1 bit rotation stressor
--rotate N
start N workers that exercise 1 bit rotates left and right of unsigned integer
variables. The default will rotate four 8, 16, 32, 64 (and if supported 128)
bit values 10000 times in a loop per bogo-op.

--rotate-method method
specify the method of rotation to use. The 'all' method uses all the methods
and is the default.

Method Description
all exercise with all the rotate stressor methods (see below):
rol8 8 bit unsigned rotate left by 1 bit
ror8 8 bit unsigned rotate right by 1 bit
rol16 16 bit unsigned rotate left by 1 bit
ror16 16 bit unsigned rotate right by 1 bit
rol32 32 bit unsigned rotate left by 1 bit
ror32 32 bit unsigned rotate right by 1 bit
rol64 64 bit unsigned rotate left by 1 bit
ror64 64 bit unsigned rotate right by 1 bit
rol128 128 bit unsigned rotate left by 1 bit
ror128 128 bit unsigned rotate right by 1 bit

--rotate-ops N
stop after N bogo rotate operations.

Restartable sequences (rseq) stressor (Linux)
--rseq N
start N workers that exercise restartable sequences via the rseq(2) system
call. This loops over a long duration critical section that is likely to be
interrupted. A rseq abort handler keeps count of the number of interruptions
and a SIGSEV handler also tracks any failed rseq aborts that can occur if
there is a mismatch in a rseq check signature. Linux only.

--rseq-ops N
stop after N bogo rseq operations. Each bogo rseq operation is equivalent to
10000 iterations over a long duration rseq handled critical section.

Real-time clock stressor
--rtc N
start N workers that exercise the real time clock (RTC) interfaces via
/dev/rtc and /sys/class/rtc/rtc0. No destructive writes (modifications) are
performed on the RTC. This is a Linux only stressor.

--rtc-ops N
stop after N bogo RTC interface accesses.

Fast process rescheduling stressor
--schedmix N
start N workers that each start child processes that repeatedly select random
a scheduling policy and then executes a short duration randomly chosen time
consuming activity. This exercises rapid re-scheduling of processes and
generates a large amount of scheduling timer interrupts.

--schedmix-ops N
stop after N scheduling mixed operations.

--schedmix-procs N
specify the number of chid processes to run for each stressor instance, range
from 1 to 64, default is 16.

Scheduling policy stressor
--schedpolicy N
start N workers that set the worker to various available scheduling policies
out of SCHED_OTHER, SCHED_BATCH, SCHED_IDLE, SCHED_FIFO, SCHED_RR and
SCHED_DEADLINE. For the real time scheduling policies a random sched priority
is selected between the minimum and maximum scheduling priority settings.

--schedpolicy-ops N
stop after N bogo scheduling policy changes.

--schedpolicy-rand
Select scheduling policy randomly so that the new policy is always different
to the previous policy. The default is to work through the scheduling policies
sequentially.

Stream control transmission protocol (SCTP) stressor
--sctp N
start N workers that perform network sctp stress activity using the Stream
Control Transmission Protocol (SCTP). This involves client/server processes
performing rapid connect, send/receives and disconnects on the local host.

--sctp-domain D
specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are
supported.

--sctp-if NAME
use network interface NAME. If the interface NAME does not exist, is not up or
does not support the domain then the loopback (lo) interface is used as the
default.

--sctp-ops N
stop sctp workers after N bogo operations.

--sctp-port P
start at sctp port P. For N sctp worker processes, ports P to (P * 4) - 1 are
used for ipv4, ipv6 domains and ports P to P - 1 are used for the unix domain.

--sctp-sched [ fcfs | prio | rr ]
specify SCTP scheduler, one of fcfs (default), prio (priority) or rr
(round-robin).

File sealing (SEAL) stressor (Linux)
--seal N
start N workers that exercise the fcntl(2) SEAL commands on a small anonymous
file created using memfd_create(2). After each SEAL command is issued the
stressor also sanity checks if the seal operation has sealed the file
correctly. (Linux only).

--seal-ops N
stop after N bogo seal operations.

Secure computing stressor
--seccomp N
start N workers that exercise Secure Computing system call filtering. Each
worker creates child processes that write a short message to /dev/null and
then exits. 2% of the child processes have a seccomp filter that disallows the
write system call and hence it is killed by seccomp with a SIGSYS. Note that
this stressor can generate many audit log messages each time the child is
killed. Requires CAP_SYS_ADMIN to run.

--seccomp-ops N
stop seccomp stress workers after N seccomp filter tests.

Secret memory stressor (Linux >= 5.11)
--secretmem N
start N workers that mmap pages using file mapping off a memfd_secret file
descriptor. Each stress loop iteration will expand the mappable region by 3
pages using ftruncate and mmap and touches the pages. The pages are then
fragmented by unmapping the middle page and then umapping the first and last
pages. This tries to force page fragmentation and also trigger out of memory
(OOM) kills of the stressor when the secret memory is exhausted. Note this is
a Linux 5.11+ only stressor and the kernel needs to be booted with
"secretmem=" option to allocate a secret memory reservation.

--secretmem-ops N
stop secretmem stress workers after N stress loop iterations.

IO seek stressor
--seek N
start N workers that randomly seeks and performs 512 byte read/write I/O
operations on a file. The default file size is 16 GB.

--seek-ops N
stop seek stress workers after N bogo seek operations.

--seek-punch
punch randomly located 8K holes into the file to cause more extents to force a
more demanding seek stressor, (Linux only).

--seek-size N
specify the size of the file in bytes. Small file sizes allow the I/O to occur
in the cache, causing greater CPU load. Large file sizes force more I/O
operations to drive causing more wait time and more I/O on the drive. One can
specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix
b, k, m or g.

POSIX semaphore stressor
--sem N
start N workers that perform POSIX semaphore wait and post operations. By
default, a parent and 4 children are started per worker to provide some
contention on the semaphore. This stresses fast semaphore operations and
produces rapid context switching.

--sem-ops N
stop semaphore stress workers after N bogo semaphore operations.

--sem-procs N
start N child workers per worker to provide contention on the semaphore, the
default is 4 and a maximum of 64 are allowed.

System V semaphore stressor
--sem-sysv N
start N workers that perform System V semaphore wait and post operations. By
default, a parent and 4 children are started per worker to provide some
contention on the semaphore. This stresses fast semaphore operations and
produces rapid context switching.

--sem-sysv-ops N
stop semaphore stress workers after N bogo System V semaphore operations.

--sem-sysv-procs N
start N child processes per worker to provide contention on the System V
semaphore, the default is 4 and a maximum of 64 are allowed.

Sendfile stressor
--sendfile N
start N workers that send an empty file to /dev/null. This operation spends
nearly all the time in the kernel. The default sendfile size is 4MB. The
sendfile options are for Linux only.

--sendfile-ops N
stop sendfile workers after N sendfile bogo operations.

--sendfile-size S
specify the size to be copied with each sendfile call. The default size is
4MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g.

Sessions stressor
--session N
start N workers that create child and grandchild processes that set and get
their session ids. 25% of the grandchild processes are not waited for by the
child to create orphaned sessions that need to be reaped by init.

--session-ops N
stop session workers after N child processes are spawned and reaped.

Setting data in the Kernel stressor
--set N
start N workers that call system calls that try to set data in the kernel,
currently these are: setgid, sethostname, setpgid, setpgrp, setuid, setgroups,
setreuid, setregid, setresuid, setresgid and setrlimit. Some of these system
calls are OS specific.

--set-ops N
stop set workers after N bogo set operations.

Shellsort stressor
--shellsort N
start N workers that sort 32 bit integers using shellsort.

--shellsort-ops N
stop shellsort stress workers after N bogo shellsorts.

--shellsort-size N
specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

POSIX shared memory stressor
--shm N
start N workers that open and allocate shared memory objects using the POSIX
shared memory interfaces. By default, the test will repeatedly create and
destroy 32 shared memory objects, each of which is 8MB in size.

--shm-bytes N
specify the size of the POSIX shared memory objects to be created. One can
specify the size as % of total available memory or in units of Bytes, KBytes,
MBytes and GBytes using the suffix b, k, m or g.

--shm-mlock
attempt to mlock shared memory objects into memory causing more memory
pressure by preventing pages from swapped out.

--shm-objs N
specify the number of shared memory objects to be created.

--shm-ops N
stop after N POSIX shared memory create and destroy bogo operations are
complete.

--shm-sysv N
start N workers that allocate shared memory using the System V shared memory
interface. By default, the test will repeatedly create and destroy 8 shared
memory segments, each of which is 8MB in size.

--shm-sysv-bytes N
specify the size of the shared memory segment to be created. One can specify
the size as % of total available memory or in units of Bytes, KBytes, MBytes
and GBytes using the suffix b, k, m or g.

--shm-sysv-mlock
attempt to mlock shared memory segment into memory causing more memory
pressure by preventing pages from swapped out.

--shm-sysv-ops N
stop after N shared memory create and destroy bogo operations are complete.

--shm-sysv-segs N
specify the number of shared memory segments to be created. The default is 8
segments.

SIGABRT stressor
--sigabrt N
start N workers that create children that are killed by SIGABRT signals or by
calling abort(3).

--sigabrt-ops N
stop the sigabrt workers after N SIGABRT signals are successfully handled.

SIGBUS stressor
--sigbus N
start N workers that rapidly create and catch bus errors generated via
misaligned access and accessing a file backed memory mapping that does not
have file storage to back the page being accessed.

--sigbus-ops N
stop sigbus stress workers after N bogo bus errors.

SIGCHLD stressor
--sigchld N
start N workers that create children to generate SIGCHLD signals. This
exercises children that exit (CLD_EXITED), get killed (CLD_KILLED), get
stopped (CLD_STOPPED) or continued (CLD_CONTINUED).

--sigchld-ops N
stop the sigchld workers after N SIGCHLD signals are successfully handled.

SIGFD stressor (Linux)
--sigfd N
start N workers that generate SIGRT signals and are handled by reads by a
child process using a file descriptor set up using signalfd(2). (Linux only).
This will generate a heavy context switch load when all CPUs are fully loaded.

--sigfd-ops
stop sigfd workers after N bogo SIGUSR1 signals are sent.

SIGFPE stressor
--sigfpe N
start N workers that rapidly cause division by zero SIGFPE faults.

--sigfpe-ops N
stop sigfpe stress workers after N bogo SIGFPE faults.

SIGIO stressor
--sigio N
start N workers that read data from a child process via a pipe and generate
SIGIO signals. This exercises asynchronous I/O via SIGIO.

--sigio-ops N
stop sigio stress workers after handling N SIGIO signals.

System signals stressor
--signal N
start N workers that exercise the signal system call three different signal
handlers, SIG_IGN (ignore), a SIGCHLD handler and SIG_DFL (default action).
For the SIGCHLD handler, the stressor sends itself a SIGCHLD signal and checks
if it has been handled. For other handlers, the stressor checks that the
SIGCHLD handler has not been called. This stress test calls the signal system
call directly when possible and will try to avoid the C library attempt to
replace signal with the more modern sigaction system call.

--signal-ops N
stop signal stress workers after N rounds of signal handler setting.

Nested signal handling stressor
--signest N
start N workers that exercise nested signal handling. A signal is raised and
inside the signal handler a different signal is raised, working through a list
of signals to exercise. An alternative signal stack is used that is large
enough to handle all the nested signal calls. The -v option will log the
approximate size of the stack required and the average stack size per nested
call.

--signest-ops N
stop after handling N nested signals.

Pending signals stressor
--sigpending N
start N workers that check if SIGUSR1 signals are pending. This stressor masks
SIGUSR1, generates a SIGUSR1 signal and uses sigpending(2) to see if the
signal is pending. Then it unmasks the signal and checks if the signal is no
longer pending.

--sigpending-ops N
stop sigpending stress workers after N bogo sigpending pending/unpending
checks.

SIGPIPE stressor
--sigpipe N
start N workers that repeatedly spawn off child process that exits before a
parent can complete a pipe write, causing a SIGPIPE signal. The child process
is either spawned using clone(2) if it is available or use the slower fork(2)
instead.

--sigpipe-ops N
stop N workers after N SIGPIPE signals have been caught and handled.

Signal queueing stressor
--sigq N
start N workers that rapidly send SIGUSR1 signals using sigqueue(3) to child
processes that wait for the signal via sigwaitinfo(2).

--sigq-ops N
stop sigq stress workers after N bogo signal send operations.

Real-time signals stressor
--sigrt N
start N workers that each create child processes to handle SIGRTMIN to SIGRMAX
real time signals. The parent sends each child process a RT signal via
siqueue(2) and the child process waits for this via sigwaitinfo(2). When the
child receives the signal it then sends a RT signal to one of the other child
processes also via sigqueue(2).

--sigrt-ops N
stop sigrt stress workers after N bogo sigqueue signal send operations.

SIGSEV stressor
--sigsegv N
start N workers that rapidly create and catch segmentation faults generated
via illegal memory access, illegal vdso system calls, illegal port reads,
illegal interrupts or access to x86 time stamp counter.

--sigsegv-ops N
stop sigsegv stress workers after N bogo segmentation faults.

Waiting for process signals stressor
--sigsuspend N
start N workers that each spawn off 4 child processes that wait for a SIGUSR1
signal from the parent using sigsuspend(2). The parent sends SIGUSR1 signals
to each child in rapid succession. Each sigsuspend wakeup is counted as one
bogo operation.

--sigsuspend-ops N
stop sigsuspend stress workers after N bogo sigsuspend wakeups.

SIGTRAP stressor
--sigtrap N
start N workers that exercise the SIGTRAP signal. For systems that support
SIGTRAP, the signal is generated using raise(SIGTRAP). Only x86 Linux systems
the SIGTRAP is also generated by an int 3 instruction.

--sigtrap-ops N
stop sigtrap stress workers after N SIGTRAPs have been handled.

SIGXCPU stressor
--sigxcpu N
start N workers that exercise the SIGXCPU stressor. A busy loop generates
SIGXCPU signals by setting a 0 second run time limit followed by a sched_yield
call.

--sigxcpu-ops N
stop sigsxcpu stress workers after N bogo SIGXCPU signal attempts.

SIGXFSZ stressor
--sigxfsz N
start N workers that exercise the SIGXFSZ stressor. A random 32 bit file size
limit is set and data is written outside this size limit to generate a SIGXFSZ
signal.

--sigxfsz-ops N
stop sigsxfsz stress workers after N bogo SIGXFSZ signal attempts.

Random memory and processor cache line stressor via a skiplist
--skiplist N
start N workers that store and then search for integers using a skiplist. By
default, 65536 integers are added and searched. This is a useful method to
exercise random access of memory and processor cache.

--skiplist-ops N
stop the skiplist worker after N skiplist store and search cycles are
completed.

--skiplist-size N
specify the size (number of integers) to store and search in the skiplist.
Size can be from 1K to 4M.

Time interrupts and context switches stressor
--sleep N
start N workers that spawn off multiple threads that each perform multiple
sleeps of ranges 1us to 0.1s. This creates multiple context switches and
timer interrupts.

--sleep-max P
start P threads per worker. The default is 1024, the maximum allowed is 30000.

--sleep-ops N
stop after N sleep bogo operations.

System management interrupts (SMI) stressor
--smi N
start N workers that attempt to generate system management interrupts (SMIs)
into the x86 ring -2 system management mode (SMM) by exercising the advanced
power management (APM) port 0xb2. This requires the --pathological option and
root privilege and is only implemented on x86 Linux platforms. This probably
does not work in a virtualized environment. The stressor will attempt to
determine the time stolen by SMIs with some naïve benchmarking.

--smi-ops N
stop after N attempts to trigger the SMI.

Network socket stressor
-S N, --sock N
start N workers that perform various socket stress activity. This involves a
pair of client/server processes performing rapid connect, send and receives
and disconnects on the local host.

--sock-domain D
specify the domain to use, the default is ipv4. Currently ipv4, ipv6 and unix
are supported.

--sock-if NAME
use network interface NAME. If the interface NAME does not exist, is not up or
does not support the domain then the loopback (lo) interface is used as the
default.

--sock-msgs N
send N messages per connect, send/receive, disconnect iteration. The default
is 1000 messages. If N is too small then the rate is throttled back by the
overhead of socket connect and disconnect (on Linux, one needs to increase
/proc/sys/net/netfilter/nf_conntrack_max to allow more connections).

--sock-nodelay
This disables the TCP Nagle algorithm, so data segments are always sent as
soon as possible. This stops data from being buffered before being
transmitted, hence resulting in poorer network utilisation and more context
switches between the sender and receiver.

--sock-ops N
stop socket stress workers after N bogo operations.

--sock-opts [ random | send | sendmsg | sendmmsg ]
by default, messages are sent using send(2). This option allows one to specify
the sending method using send(2), sendmsg(2), sendmmsg(2) or a random
selection of one of these 3 on each iteration. Note that sendmmsg is only
available for Linux systems that support this system call.

--sock-port P
start at socket port P. For N socket worker processes, ports P to P - 1 are
used.

--sock-protocol P
Use the specified protocol P, default is tcp. Options are tcp and mptcp (if
supported by the operating system).

--sock-type [ stream | seqpacket ]
specify the socket type to use. The default type is stream. seqpacket
currently only works for the unix socket domain.

--sock-zerocopy
enable zerocopy for send and recv calls if the MSG_ZEROCOPY is supported.

Socket abusing stressor
--sockabuse N
start N workers that abuse a socket file descriptor with various file based
system that don't normally act on sockets. The kernel should handle these
illegal and unexpected calls gracefully.

--sockabuse-ops N
stop after N iterations of the socket abusing stressor loop.

--sockabuse-port P
start at socket port P. For N sockabuse worker processes, ports P to P - 1 are
used.

Socket diagnostic stressor (Linux)
--sockdiag N
start N workers that exercise the Linux sock_diag netlink socket diagnostics
(Linux only). This currently requests diagnostics using UDIAG_SHOW_NAME,
UDIAG_SHOW_VFS, UDIAG_SHOW_PEER, UDIAG_SHOW_ICONS, UDIAG_SHOW_RQLEN and
UDIAG_SHOW_MEMINFO for the AF_UNIX family of socket connections.

--sockdiag-ops N
stop after receiving N sock_diag diagnostic messages.

Socket file descriptor stressor
--sockfd N
start N workers that pass file descriptors over a UNIX domain socket using the
CMSG(3) ancillary data mechanism. For each worker, pair of client/server
processes are created, the server opens as many file descriptors on /dev/null
as possible and passing these over the socket to a client that reads these
from the CMSG data and immediately closes the files.

--sockfd-ops N
stop sockfd stress workers after N bogo operations.

--sockfd-port P
start at socket port P. For N socket worker processes, ports P to P - 1 are
used.

Opening network socket stressor
--sockmany N
start N workers that use a client process to attempt to open as many as 100000
TCP/IP socket connections to a server on port 10000.

--sockmany-if NAME
use network interface NAME. If the interface NAME does not exist, is not up or
does not support the domain then the loopback (lo) interface is used as the
default.

--sockmany-ops N
stop after N connections.

--sockmany-port P
start at socket port P. For N sockmany worker processes, ports P to P - 1 are
used.

Socket I/O stressor
--sockpair N
start N workers that perform socket pair I/O read/writes. This involves a pair
of client/server processes performing randomly sized socket I/O operations.

--sockpair-ops N
stop socket pair stress workers after N bogo operations.

Softlockup stressor
--softlockup N
start N workers that flip between with the "real-time" SCHED_FIO and SCHED_RR
scheduling policies at the highest priority to force softlockups. This can
only be run with CAP_SYS_NICE capability and for best results the number of
stressors should be at least the number of online CPUs. Once running, this is
practically impossible to stop and it will force softlockup issues and may
trigger watchdog timeout reboots.

--softlockup-ops N
stop softlockup stress workers after N bogo scheduler policy changes.

Sparse matrix stressor
--sparsematrix N
start N workers that exercise 3 different sparse matrix implementations based
on hashing, Judy array (for 64 bit systems), 2-d circular linked-lists, memory
mapped 2-d matrix (non-sparse), quick hashing (on preallocated nodes) and red-
black tree. The sparse matrix is populated with values, random values
potentially non-existing values are read, known existing values are read and
known existing values are marked as zero. This default 500 × 500 sparse matrix
is used and 5000 items are put into the sparse matrix making it 2% utilized.

--sparsematrix-items N
populate the sparse matrix with N items. If N is greater than the number of
elements in the sparse matrix than N will be capped to create at 100% full
sparse matrix.

Method Description
all exercise with all the sparsematrix stressor methods (see below):
hash use a hash table and allocate nodes on the heap for each unique
value at a (x, y) matrix position.
hashjudy use a hash table for x coordinates and a Judy array for y
coordinates for values at a (x, y) matrix position.
judy use a Judy array with a unique 1-to-1 mapping of (x, y) matrix
position into the array.
list use a circular linked-list for sparse y positions each with circular
linked-lists for sparse x positions for the (x, y) matrix
coordinates.
mmap use a non-sparse mmap the entire 2-d matrix space. Only (x, y)
matrix positions that are referenced will get physically mapped.
Note that large sparse matrices cannot be mmap'd due to lack of
virtual address limitations, and too many referenced pages can
trigger the out of memory killer on Linux.
qhash use a hash table with pre-allocated nodes for each unique value.
This is a quick hash table implementation, nodes are not allocated
each time with calloc and are allocated from a pre-allocated pool
leading to quicker hash table performance than the hash method.
rb use a red-black balanced tree using one tree node for each unique
value at a (x, y) matrix position.
splay use a splay tree using one tree node for each unique value at a (x,
y) matrix position.

--sparsematrix-ops N
stop after N sparsematrix test iterations.

--sparsematrix-size N
use a N × N sized sparse matrix

POSIX process spawn (posix_spawn) stressor (Linux)
--spawn N
start N workers continually spawn children using posix_spawn(3) that exec
stress-ng and then exit almost immediately. Currently Linux only.

--spawn-ops N
stop spawn stress workers after N bogo spawns.

Splice stressor (Linux)
--splice N
move data from /dev/zero to /dev/null through a pipe without any copying
between kernel address space and user address space using splice(2). This is
only available for Linux.

--splice-bytes N
transfer N bytes per splice call, the default is 64K. One can specify the size
as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g.

--splice-ops N
stop after N bogo splice operations.

Stack stressor
--stack N
start N workers that rapidly cause and catch stack overflows by use of large
recursive stack allocations. Much like the brk stressor, this can eat up
pages rapidly and may trigger the kernel OOM killer on the process, however,
the killed stressor is respawned again by a monitoring parent process.

--stack-fill
the default action is to touch the lowest page on each stack allocation. This
option touches all the pages by filling the new stack allocation with zeros
which forces physical pages to be allocated and hence is more aggressive.

--stack-mlock
attempt to mlock stack pages into memory causing more memory pressure by
preventing pages from swapped out.

--stack-ops N
stop stack stress workers after N bogo stack overflows.

--stack-pageout
force stack pages out to swap (available when madvise(2) supports
MADV_PAGEOUT).

--stack-unmap
unmap a single page in the middle of a large buffer allocated on the stack on
each stack allocation. This forces the stack mapping into multiple separate
allocation mappings.

Dirty page and stack exception stressor
--stackmmap N
start N workers that use a 2MB stack that is memory mapped onto a temporary
file. A recursive function works down the stack and flushes dirty stack pages
back to the memory mapped file using msync(2) until the end of the stack is
reached (stack overflow). This exercises dirty page and stack exception
handling.

--stackmmap-ops N
stop workers after N stack overflows have occurred.

Libc string functions stressor
--str N
start N workers that exercise various libc string functions on random strings.

--str-method strfunc
select a specific libc string function to stress. Available string functions
to stress are: all, index, rindex, strcasecmp, strcat, strchr, strcoll,
strcmp, strcpy, strlen, strncasecmp, strncat, strncmp, strrchr and strxfrm.
See string(3) for more information on these string functions. The 'all'
method is the default and will exercise all the string methods.

--str-ops N
stop after N bogo string operations.

STREAM memory stressor
--stream N
start N workers exercising a memory bandwidth stressor very loosely based on
the STREAM "Sustainable Memory Bandwidth in High Performance Computers"
benchmarking tool by John D. McCalpin, Ph.D. This stressor allocates buffers
that are at least 4 times the size of the CPU L2 cache and continually
performs rounds of following computations on large arrays of double precision
floating point numbers:

Operation Description
copy c[i] = a[i]
scale b[i] = scalar * c[i]
add c[i] = a[i] + b[i]
triad a[i] = b[i] + (c[i] * scalar)

Since this is loosely based on a variant of the STREAM benchmark code, DO NOT
submit results based on this as it is intended to in stress-ng just to stress
memory and compute and NOT intended for STREAM accurate tuned or non-tuned
benchmarking whatsoever. Use the official STREAM benchmarking tool if you
desire accurate and standardised STREAM benchmarks.

The stressor calculates the memory read rate, memory write rate and floating
point operations rate. These will differ from the maximum theoretical
read/write/compute rates because of loop overheads and the use of volatile
pointers to ensure the compiler does not optimize out stores.

--stream-index N
specify number of stream indices used to index into the data arrays a, b and
c. This adds indirection into the data lookup by using randomly shuffled
indexing into the three data arrays. Level 0 (no indexing) is the default, and
3 is where all 3 arrays are indexed via 3 different randomly shuffled indexes.
The higher the index setting the more impact this has on L1, L2 and L3 caching
and hence forces higher memory read/write latencies.

--stream-l3-size N
Specify the CPU Level 3 cache size in bytes. One can specify the size in
units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. If
the L3 cache size is not provided, then stress-ng will attempt to determine
the cache size, and failing this, will default the size to 4MB.

--stream-mlock
attempt to mlock the stream buffers into memory to prevent them from being
swapped out.

--stream-madvise [ collapse | hugepage | nohugepage | normal ]
Specify the madvise options used on the memory mapped buffer used in the
stream stressor. Non-linux systems will only have the 'normal' madvise advice.
The default is 'normal'.

--stream-ops N
stop after N stream bogo operations, where a bogo operation is one round of
copy, scale, add and triad operations.

Swap partitions stressor (Linux)
--swap N
start N workers that add and remove small randomly sizes swap partitions
(Linux only). Note that if too many swap partitions are added then the
stressors may exit with exit code 3 (not enough resources). Requires
CAP_SYS_ADMIN to run.

--swap-ops N
stop the swap workers after N swapon/swapoff iterations.

Context switching between mutually tied processes stressor
-s N, --switch N
start N workers that force context switching between two mutually
blocking/unblocking tied processes. By default message passing over a pipe is
used, but different methods are available.

--switch-freq F
run the context switching at the frequency of F context switches per second.
Note that the specified switch rate may not be achieved because of CPU speed
and memory bandwidth limitations.

--switch-method [ mq | pipe | sem-sysv ]
select the preferred context switch block/run synchronization method, these
are as follows:

Method Description
mq use posix message queue with a 1 item size. Messages are passed
between a sender and receiver process.
pipe single character messages are passed down a single character sized
pipe between a sender and receiver process.
sem-sysv a SYSV semaphore is used to block/run two processes.

--switch-ops N
stop context switching workers after N bogo operations.

Symlink stressor
--symlink N
start N workers creating and removing symbolic links.

--symlink-ops N
stop symlink stress workers after N bogo operations.

--symlink-sync
sync dirty data and metadata to disk.

Partial file syncing (sync_file_range) stressor
--sync-file N
start N workers that perform a range of data syncs across a file using
sync_file_range(2). Three mixes of syncs are performed, from start to the end
of the file, from end of the file to the start, and a random mix. A random
selection of valid sync types are used, covering the
SYNC_FILE_RANGE_WAIT_BEFORE, SYNC_FILE_RANGE_WRITE and
SYNC_FILE_RANGE_WAIT_AFTER flag bits.

--sync-file-bytes N
specify the size of the file to be sync'd. One can specify the size as % of
free space on the file system in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g.

--sync-file-ops N
stop sync-file workers after N bogo sync operations.

CPU synchronized loads stressor
--syncload N
start N workers that produce sporadic short lived loads synchronized across N
stressor processes. By default repeated cycles of 125ms busy load followed by
62.5ms sleep occur across all the workers in step to create bursts of load to
exercise C state transitions and CPU frequency scaling. The busy load and
sleeps have +/-10% jitter added to try exercising scheduling patterns.

--syncload-msbusy M
specify the busy load duration in milliseconds.

--syncload-mssleep M
specify the sleep duration in milliseconds.

--syncload-ops N
stop syncload workers after N load/sleep cycles.

System calls bad address and fault handling stressor
--sysbadaddr N
start N workers that pass bad addresses to system calls to exercise bad
address and fault handling. The addresses used are null pointers, read only
pages, write only pages, unmapped addresses, text only pages, unaligned
addresses and top of memory addresses.

--sysbadaddr-ops N
stop the sysbadaddr stressors after N bogo system calls.

System calls stressor
--syscall N
start N workers that exercise a range of available system calls. System calls
that fail due to lack of capabilities or errors are ignored. The stressor will
try to maximize the rate of system calls being executed based the entire time
taken to setup, run and cleanup after each system call.

--syscall-method method
select the choice of system calls to executed based on the fastest test
duration times. Note that this includes the time to setup, execute the system
call and cleanup afterwards. The available methods are as follows:

Method Description

all select all the available system calls
fast10 select the fastest 10% system call tests
fast25 select the fastest 25% system call tests
fast50 select the fastest 50% system call tests
fast75 select the fastest 75% system call tests
fast90 select the fastest 90% system call tests
geomean1 select tests that are less or equal to the geometric mean of all
the test times
geomean1 select tests that are less or equal to 2 × the geometric mean of
all the test times
geomean1 select tests that are less or equal to 3 × the geometric mean of
all the test times

--syscall-ops N
stop after N system calls

--sycsall-top N
report the fastest top N system calls. Setting N to zero will report all the
system calls that could be exercised.

System information stressor
--sysinfo N
start N workers that continually read system and process specific information.
This reads the process user and system times using the times(2) system call.
For Linux systems, it also reads overall system statistics using the
sysinfo(2) system call and also the file system statistics for all mounted
file systems using statfs(2).

--sysinfo-ops N
stop the sysinfo workers after N bogo operations.

System calls with invalid arguments stressor (Linux)
--sysinval N
start N workers that exercise system calls in random order with permutations
of invalid arguments to force kernel error handling checks. The stress test
autodetects system calls that cause processes to crash or exit prematurely and
will blocklist these after several repeated breakages. System call arguments
that cause system calls to work successfully are also detected an blocklisted
too. Linux only.

--sysinval-ops N
stop sysinval workers after N system call attempts.

/sys stressor (Linux)
--sysfs N
start N workers that recursively read files from /sys (Linux only). This may
cause specific kernel drivers to emit messages into the kernel log.

--sysfs-ops N
stop sysfs reading after N bogo read operations. Note, since the number of
entries may vary between kernels, this bogo ops metric is probably very
misleading.

Tee stressor (Linux)
--tee N
move data from a writer process to a reader process through pipes and to
/dev/null without any copying between kernel address space and user address
space using tee(2). This is only available for Linux.

--tee-ops N
stop after N bogo tee operations.

Timer event stressor (Linux)
-T N, --timer N
start N workers creating timer events at a default rate of 1 MHz (Linux only);
this can create a many thousands of timer clock interrupts. Each timer event
is caught by a signal handler and counted as a bogo timer op.

--timer-freq F
run timers at F Hz; range from 1 to 1000000000 Hz (Linux only). By selecting
an appropriate frequency stress-ng can generate hundreds of thousands of
interrupts per second. Note: it is also worth using --timer-slack 0 for high
frequencies to stop the kernel from coalescing timer events.

--timer-ops N
stop timer stress workers after N bogo timer events (Linux only).

--timer-rand
select a timer frequency based around the timer frequency +/- 12.5% random
jitter. This tries to force more variability in the timer interval to make the
scheduling less predictable.

Timerfd stressor (Linux)
--timerfd N
start N workers creating timerfd events at a default rate of 1 MHz (Linux
only); this can create a many thousands of timer clock events. Timer events
are waited for on the timer file descriptor using select(2) and then read and
counted as a bogo timerfd op.

--timerfs-fds N
try to use a maximum of N timerfd file descriptors per stressor.

--timerfd-freq F
run timers at F Hz; range from 1 to 1000000000 Hz (Linux only). By selecting
an appropriate frequency stress-ng can generate hundreds of thousands of
interrupts per second.

--timerfd-ops N
stop timerfd stress workers after N bogo timerfd events (Linux only).

--timerfd-rand
select a timerfd frequency based around the timer frequency +/- 12.5% random
jitter. This tries to force more variability in the timer interval to make the
scheduling less predictable.

Time warp stressor
--time-warp N
start N workers that read the system time and where appropriate for monotonic
clocks perform a check for reverse time warping. At the end of the run there
are time wrap-around checks. This stressor exercises clock_gettime(2) on all
available clocks, gettimeofday(2), time(2) and getrusage(2) to check for
unexpected time behaviour. Note that only some clocks are reliably monotonic.

--time-warp-ops N
stop after N rounds of checking all the available clocks and time fetching
system calls.

Translation lookaside buffer shootdowns stressor
--tlb-shootdown N
start N workers that force Translation Lookaside Buffer (TLB) shootdowns.
This is achieved by creating up to 16 child processes that all share a region
of memory and these processes are shared amongst the available CPUs. The
processes adjust the page mapping settings causing TLBs to be force flushed on
the other processors, causing the TLB shootdowns.

--tlb-shootdown-ops N
stop after N bogo TLB shootdown operations are completed.

Tmpfs stressor
--tmpfs N
start N workers that create a temporary file on an available tmpfs file system
and perform various file based mmap operations upon it.

--tmpfs-mmap-async
enable file based memory mapping and use asynchronous msync'ing on each page,
see --tmpfs-mmap-file.

--tmpfs-mmap-file
enable tmpfs file based memory mapping and by default use synchronous
msync'ing on each page.

--tmpfs-ops N
stop tmpfs stressors after N bogo mmap operations.

Touching files stressor
--touch N
touch files by using open(2) or creat(2) and then closing and unlinking them.
The filename contains the bogo-op number and is incremented on each touch
operation, hence this fills the dentry cache. Note that the user time and
system time may be very low as most of the run time is waiting for file I/O
and this produces very large bogo-op rates for the very low CPU time used.

--touch-method [ random | open | creat ]
select the method the file is created, either randomly using open(2) or
create(2), just using open(2) with the O_CREAT open flag, or with creat(2).

--touch-ops N
stop the touch workers after N file touches.

--touch-opts all, direct, dsync, excl, noatime, sync
specify various file open options as a comma separated list. Options are as
follows:

Option Description
all use all the open options, namely direct, dsync, excl, noatime and
sync
direct try to minimize cache effects of the I/O to and from this file,
using the O_DIRECT open flag.
dsync ensure output has been transferred to underlying hardware and file
metadata has been updated using the O_DSYNC open flag.
excl fail if file already exists (it should not).
noatime do not update the file last access time if the file is read.
sync ensure output has been transferred to underlying hardware using the
O_SYNC open flag.

Tree data structures stressor
--tree N
start N workers that exercise tree data structures. The default is to add,
find and remove 250,000 64 bit integers into AVL (avl), Red-Black (rb), Splay
(splay), btree and binary trees. The intention of this stressor is to
exercise memory and cache with the various tree operations.

--tree-ops N
stop tree stressors after N bogo ops. A bogo op covers the addition, finding
and removing all the items into the tree(s).

--tree-size N
specify the size of the tree, where N is the number of 64 bit integers to be
added into the tree.

Trigonometric functions stressor
--trig N
start N workers that exercise sin, cos, sincos (where available) and tan
trigonometric functions using float, double and long double floating point
variants. Each function is exercised 10,000 times per bogo-operation.

--trig-method function
specify a trigonometric stress function. By default, all the functions are
exercised sequentially, however one can specify just one function to be used
if required. Available options are as follows:

Method Description
all iterate through all of the following trigonometric functions
cos cosine (double precision)
cosf cosine (float precision)
cosl cosine (long double precision)
sin sine (double precision)
sinf sine (float precision)
sinl sine (long double precision)
sincos sine and cosine (double precision)
sincosf sine and cosine (float precision)
sincosl sine and cosine (long double precision)
tan tangent (double precision)

tanf tangent (float precision)
tanl tangent (long double precision)

--trig-ops N
stop after N bogo-operations.

Time stamp counter (TSC) stressor
--tsc N
start N workers that read the Time Stamp Counter (TSC) 256 times per loop
iteration (bogo operation). This exercises the tsc instruction for x86, the
mftb instruction for ppc64, the rdcycle instruction for RISC-V, the tick
instruction on SPARC and the rdtime.d instruction for Loong64.

--tsc-lfence
add lfence after each tsc read to force serialization (x86 only).

--tsc-ops N
stop the tsc workers after N bogo operations are completed.

--tsc-rdtscp
use the rdtscp instruction instead of rdtsc (x86 only). This also disables the
--tsc-lfence option.

Binary tree stressor
--tsearch N
start N workers that insert, search and delete 32 bit integers on a binary
tree using tsearch(3), tfind(3) and tdelete(3). By default, there are 65536
randomized integers used in the tree. This is a useful method to exercise
random access of memory and processor cache.

--tsearch-ops N
stop the tsearch workers after N bogo tree operations are completed.

--tsearch-size N
specify the size (number of 32 bit integers) in the array to tsearch. Size can
be from 1K to 4M.

Network tunnel stressor
--tun N
start N workers that create a network tunnel device and sends and receives
packets over the tunnel using UDP and then destroys it. A new random
192.168.*.* IPv4 address is used each time a tunnel is created.

--tun-ops N
stop after N iterations of creating/sending/receiving/destroying a tunnel.

--tun-tap
use network tap device using level 2 frames (bridging) rather than a tun
device for level 3 raw packets (tunnelling).

UDP network stressor
--udp N
start N workers that transmit data using UDP. This involves a pair of
client/server processes performing rapid connect, send and receives and
disconnects on the local host.

--udp-domain D
specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are
supported.

--udp-gro
enable UDP-GRO (Generic Receive Offload) if supported.

--udp-if NAME
use network interface NAME. If the interface NAME does not exist, is not up or
does not support the domain then the loopback (lo) interface is used as the
default.

--udp-lite
use the UDP-Lite (RFC 3828) protocol (only for ipv4 and ipv6 domains).

--udp-ops N
stop udp stress workers after N bogo operations.

--udp-port P
start at port P. For N udp worker processes, ports P to P - 1 are used. By
default, ports 7000 upwards are used.

UDP flooding stressor
--udp-flood N
start N workers that attempt to flood the host with UDP packets to random
ports. The IP address of the packets are currently not spoofed. This is only
available on systems that support AF_PACKET.

--udp-flood-domain D
specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are
supported.

--udp-flood-if NAME
use network interface NAME. If the interface NAME does not exist, is not up or
does not support the domain then the loopback (lo) interface is used as the
default.

--udp-flood-ops N
stop udp-flood stress workers after N bogo operations.

Umount stressor
--umount N
start N workers that exercise mounting and racying unmounting of small tmpfs
and ramfs file systems. Three child processes are invoked, one to mount,
another to force umount and a third to exercice /proc/mounts. Small random
delays are used between mount and umount calls to try to trigger race
conditions on the umount calls.

--umount-ops N
stop umount workers after N successful bogo mount/umount operations.

Unshare stressor (Linux)
--unshare N
start N workers that each fork off 32 child processes, each of which exercises
the unshare(2) system call by disassociating parts of the process execution
context. (Linux only).

--unshare-ops N
stop after N bogo unshare operations.

Uprobe stressor (Linux)
--uprobe N
start N workers that trace the entry to libc function getpid() using the Linux
uprobe kernel tracing mechanism. This requires CAP_SYS_ADMIN capabilities and
a modern Linux uprobe capable kernel.

--uprobe-ops N
stop uprobe tracing after N trace events of the function that is being traced.

/dev/urandom stressor (Linux)
-u N, --urandom N
start N workers reading /dev/urandom (Linux only). This will load the kernel
random number source.

--urandom-ops N
stop urandom stress workers after N urandom bogo read operations (Linux only).

Page faults stressor (Linux)
--userfaultfd N
start N workers that generate write page faults on a small anonymously mapped
memory region and handle these faults using the user space fault handling via
the userfaultfd mechanism. This will generate a large quantity of major page
faults and also context switches during the handling of the page faults.
(Linux only).

--userfaultfd-bytes N
mmap N bytes per userfaultfd worker to page fault on, the default is 16MB.
One can specify the size as % of total available memory or in units of Bytes,
KBytes, MBytes and GBytes using the suffix b, k, m or g.

--userfaultfd-ops N
stop userfaultfd stress workers after N page faults.

SYGSYS stressor
--usersyscall N
start N workers that exercise the Linux prctl userspace system call mechanism.
A userspace system call is handled by a SIGSYS signal handler and exercised
with the system call disabled (ENOSYS) and enabled (via SIGSYS) using prctl
PR_SET_SYSCALL_USER_DISPATCH.

--usersyscall-ops N
stop after N successful userspace syscalls via a SIGSYS signal handler.

File timestamp stressor
--utime N
start N workers updating file timestamps. This is mainly CPU bound when the
default is used as the system flushes metadata changes only periodically.

--utime-fsync
force metadata changes on each file timestamp update to be flushed to disk.
This forces the test to become I/O bound and will result in many dirty
metadata writes.

--utime-ops N
stop utime stress workers after N utime bogo operations.

Virtual dynamic shared object stressor
--vdso N
start N workers that repeatedly call each of the system call functions in the
vDSO (virtual dynamic shared object). The vDSO is a shared library that the
kernel maps into the address space of all user-space applications to allow
fast access to kernel data to some system calls without the need of performing
an expensive system call.

--vdso-func F
Instead of calling all the vDSO functions, just call the vDSO function F. The
functions depend on the kernel being used, but are typically clock_gettime,
getcpu, gettimeofday and time.

--vdso-ops N
stop after N vDSO functions calls.

Vector floating point operations stressor
--vecfp N
start N workers that exericise floating point (single and double precision)
addition, multiplication, division and negation on vectors of 128, 64, 32, 16
and 8 floating point values. The -v option will show the approximate
throughput in millions of floating pointer operations per second for each
operation. For x86, the gcc/clang target clones attribute has been used to
produced vector optimizations for a range of mmx, sse, avx and processor
features.

--vecfp-method method
specify a vecfp stress method. By default, all the stress methods are
exercised sequentially, however one can specify just one method to be used if
required.

Method Description
all iterate through all of the following vector methods
floatv128add addition of a vector of 128 single precision floating point
values
floatv64add addition of a vector of 64 single precision floating point
values
floatv32add addition of a vector of 32 single precision floating point
values
floatv16add addition of a vector of 16 single precision floating point
values
floatv8add addition of a vector of 8 single precision floating point
values
floatv128mul multiplication of a vector of 128 single precision floating
point values
floatv64mul multiplication of a vector of 64 single precision floating
point values
floatv32mul multiplication of a vector of 32 single precision floating
point values

floatv16mul multiplication of a vector of 16 single precision floating
point values
floatv8mul multiplication of a vector of 8 single precision floating point
values
floatv128div division of a vector of 128 single precision floating point
values
floatv64div division of a vector of 64 single precision floating point
values
floatv32div division of a vector of 32 single precision floating point
values
floatv16div division of a vector of 16 single precision floating point
values
floatv8div division of a vector of 8 single precision floating point
values
doublev128add addition of a vector of 128 double precision floating point
values
doublev64add addition of a vector of 64 double precision floating point
values
doublev32add addition of a vector of 32 double precision floating point
values
doublev16add addition of a vector of 16 double precision floating point
values
doublev8add addition of a vector of 8 double precision floating point
values
doublev128mul multiplication of a vector of 128 double precision floating
point values
doublev64mul multiplication of a vector of 64 double precision floating
point values
doublev32mul multiplication of a vector of 32 double precision floating
point values
doublev16mul multiplication of a vector of 16 double precision floating
point values
doublev8mul multiplication of a vector of 8 double precision floating point
values
doublev128div division of a vector of 128 double precision floating point
values
doublev64div division of a vector of 64 double precision floating point
values
doublev32div division of a vector of 32 double precision floating point
values
doublev16div division of a vector of 16 double precision floating point
values
doublev8div division of a vector of 8 double precision floating point
values
doublev128neg negation of a vector of 128 double precision floating point
values
doublev64neg negation of a vector of 64 double precision floating point
values
doublev32neg negation of a vector of 32 double precision floating point
values
doublev16neg negation of a vector of 16 double precision floating point
values
doublev8neg negation of a vector of 8 double precision floating point
values

--vecfp-ops N
stop after N vector floating point bogo-operations. Each bogo-op is equivalent
to 65536 loops of 2 vector operations. For example, one bogo-op on a 16 wide
vector is equivalent to 65536 × 2 × 16 floating point operations.

Vector math operations stressor
--vecmath N
start N workers that perform various unsigned integer math operations on
various 128 bit vectors. A mix of vector math operations are performed on the
following vectors: 16 × 8 bits, 8 × 16 bits, 4 × 32 bits, 2 × 64 bits. The
metrics produced by this mix depend on the processor architecture and the
vector math optimisations produced by the compiler.

--vecmath-ops N
stop after N bogo vector integer math operations.

Shuffled vector math operations stressor
--vecshuf N
start N workers that shuffle data on various 64 byte vectors comprised of 8,
16, 32, 64 and 128 bit unsigned integers. The integers are shuffled around the
vector with 4 shuffle operations per loop, 65536 loops make up one bogo-op of
shuffling. The data shuffling rates and shuffle operation rates are logged
when using the -v option. This stressor exercises vector load,
shuffle/permute, packing/unpacking and store operations.

--vecshuf-method method
specify a vector shuffling stress method. By default, all the stress methods
are exercised sequentially, however one can specify just one method to be used
if required.

Method Description
all iterate through all of the following vector methods
u8x64 shuffle a vector of 64 unsigned 8 bit integers
u16x32 shuffle a vector of 32 unsigned 16 bit integers
u32x16 shuffle a vector of 16 unsigned 32 bit integers
u64x8 shuffle a vector of 8 unsigned 64 bit integers
u128x4 shuffle a vector of 4 unsigned 128 bit integers (when supported)

--vecshuf-ops N
stop after N bogo vector shuffle ops. One bogo-op is equavlent of 4 × 65536
vector shuffle operations on 64 bytes of vector data.

Wide vector math operations stressor
--vecwide N
start N workers that perform various 8 bit math operations on vectors of 4, 8,
16, 32, 64, 128, 256, 512, 1024 and 2048 bytes. With the -v option the
relative compute performance vs the expected compute performance based on
total run time is shown for the first vecwide worker. The vecwide stressor
exercises various processor vector instruction mixes and how well the compiler
can map the vector operations to the target instruction set.

--vecwide-ops N
stop after N bogo vector operations (2048 iterations of a mix of vector
instruction operations).

File based authenticy protection (verity) stressor
--verity N
start N workers that exercise read-only file based authenticy protection using
the verity ioctls FS_IOC_ENABLE_VERITY and FS_IOC_MEASURE_VERITY. This
requires file systems with verity support (currently ext4 and f2fs on Linux)
with the verity feature enabled. The test attempts to creates a small file
with multiple small extents and enables verity on the file and verifies it. It
also checks to see if the file has verity enabled with the FS_VERITY_FL bit
set on the file flags.

--verity-ops N
stop the verity workers after N file create, enable verity, check verity and
unlink cycles.

vfork stressor
--vfork N
start N workers continually vforking children that immediately exit.

--vfork-max P
create P processes and then wait for them to exit per iteration. The default
is just 1; higher values will create many temporary zombie processes that are
waiting to be reaped. One can potentially fill up the process table using high
values for --vfork-max and --vfork.

--vfork-ops N
stop vfork stress workers after N bogo operations.

--vfork-vm
deprecated since stress-ng V0.14.03

vfork processes as much as possible stressor
--vforkmany N
start N workers that spawn off a chain of vfork children until the process
table fills up and/or vfork fails. vfork can rapidly create child processes
and the parent process has to wait until the child dies, so this stressor
rapidly fills up the process table.

--vforkmany-ops N
stop vforkmany stressors after N vforks have been made.

--vforkmany-vm
enable detrimental performance virtual memory advice using madvise on all
pages of the vforked process. Where possible this will try to set every page
in the new process with using madvise MADV_MERGEABLE, MADV_WILLNEED,
MADV_HUGEPAGE and MADV_RANDOM flags. Linux only.

--vforkmany-vm-bytes N
mmap N bytes per vm worker for more memory pressure, the default is 64MB. This
also enables the --vforkmany-vm option. One can specify the size as % of
total available memory or in units of Bytes, KBytes, MBytes and GBytes using
the suffix b, k, m or g.

Memory allocate and write stressor
-m N, --vm N
start N workers continuously calling mmap(2)/munmap(2) and writing to the
allocated memory. Note that this can cause systems to trip the kernel OOM
killer on Linux systems if not enough physical memory and swap is not
available.

--vm-bytes N
mmap N bytes per vm worker, the default is 256MB. One can specify the size as
% of total available memory or in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g.

--vm-hang N
sleep N seconds before unmapping memory, the default is zero seconds.
Specifying 0 will do an infinite wait.

--vm-keep
do not continually unmap and map memory, just keep on re-writing to it.

--vm-locked
Lock the pages of the mapped region into memory using mmap MAP_LOCKED (since
Linux 2.5.37). This is similar to locking memory as described in mlock(2).

--vm-madvise advice
Specify the madvise 'advice' option used on the memory mapped regions used in
the vm stressor. Non-linux systems will only have the 'normal' madvise advice,
linux systems support 'dontneed', 'hugepage', 'mergeable' , 'nohugepage',
'normal', 'random', 'sequential', 'unmergeable' and 'willneed' advice. If this
option is not used then the default is to pick random madvise advice for each
mmap call. See madvise(2) for more details.

--vm-method method
specify a vm stress method. By default, all the stress methods are exercised
sequentially, however one can specify just one method to be used if required.
Each of the vm workers have 3 phases:

1. Initialised. The anonymously memory mapped region is set to a known
pattern.

2. Exercised. Memory is modified in a known predictable way. Some vm workers
alter memory sequentially, some use small or large strides to step along
memory.

3. Checked. The modified memory is checked to see if it matches the expected
result.

The vm methods containing 'prime' in their name have a stride of the largest
prime less than 2↑64, allowing to them to thoroughly step through memory and
touch all locations just once while also doing without touching memory cells
next to each other. This strategy exercises the cache and page non-locality.

Since the memory being exercised is virtually mapped then there is no
guarantee of touching page addresses in any particular physical order. These
workers should not be used to test that all the system's memory is working
correctly either, use tools such as memtest86 instead.

The vm stress methods are intended to exercise memory in ways to possibly find
memory issues and to try to force thermal errors.

Available vm stress methods are described as follows:

Method Description
all iterate over all the vm stress methods as listed below.

cache-lines work through memory in 64 byte cache sized steps writing a
single byte per cache line. Once the write is complete, the
memory is read to verify the values are written correctly.
cache-stripe work through memory in 64 byte cache sized chunks, writing in
ascending address order on even offsets and descending address
order on odd offsets.
checkboard work through memory writing alternative zero/one bit values into
memory in a mixed checkerboard pattern. Memory is swapped around
to ensure every bit is read, bit flipped and re-written and then
re-read for verification.
flip sequentially work through memory 8 times, each time just one bit
in memory flipped (inverted). This will effectively invert each
byte in 8 passes.
fwdrev write to even addressed bytes in a forward direction and odd
addressed bytes in reverse direction. rhe contents are sanity
checked once all the addresses have been written to.
galpat-0 galloping pattern zeros. This sets all bits to 0 and flips just
1 in 4096 bits to 1. It then checks to see if the 1s are pulled
down to 0 by their neighbours or of the neighbours have been
pulled up to 1.
galpat-1 galloping pattern ones. This sets all bits to 1 and flips just 1
in 4096 bits to 0. It then checks to see if the 0s are pulled up
to 1 by their neighbours or of the neighbours have been pulled
down to 0.
gray fill the memory with sequential gray codes (these only change 1
bit at a time between adjacent bytes) and then check if they are
set correctly.
grayflip fill memory with adjacent bytes of gray code and inverted gray
code pairs to change as many bits at a time between adjacent
bytes and check if these are set correctly.
incdec work sequentially through memory twice, the first pass
increments each byte by a specific value and the second pass
decrements each byte back to the original start value. The
increment/decrement value changes on each invocation of the
stressor.
inc-nybble initialise memory to a set value (that changes on each
invocation of the stressor) and then sequentially work through
each byte incrementing the bottom 4 bits by 1 and the top 4 bits
by 15.
lfsr32 fill memory with values generated from a 32 bit Galois linear
feedback shift register using the polynomial x↑32 + x↑31 + x↑29
+ x + 1. This generates a ring of 2↑32 - 1 unique values (all
32 bit values except for 0).
rand-set sequentially work through memory in 64 bit chunks setting bytes
in the chunk to the same 8 bit random value. The random value
changes on each chunk. Check that the values have not changed.
rand-sum sequentially set all memory to random values and then summate
the number of bits that have changed from the original set
values.
read64 sequentially read memory using 32 × 64 bit reads per bogo loop.
Each loop equates to one bogo operation. This exercises raw
memory reads.
ror fill memory with a random pattern and then sequentially rotate
64 bits of memory right by one bit, then check the final
load/rotate/stored values.
swap fill memory in 64 byte chunks with random patterns. Then swap
each 64 chunk with a randomly chosen chunk. Finally, reverse the
swap to put the chunks back to their original place and check if
the data is correct. This exercises adjacent and random memory
load/stores.
move-inv sequentially fill memory 64 bits of memory at a time with random
values, and then check if the memory is set correctly. Next,
sequentially invert each 64 bit pattern and again check if the
memory is set as expected.
modulo-x fill memory over 23 iterations. Each iteration starts one byte
further along from the start of the memory and steps along in 23
byte strides. In each stride, the first byte is set to a random
pattern and all other bytes are set to the inverse. Then it
checks see if the first byte contains the expected random
pattern. This exercises cache store/reads as well as seeing if
neighbouring cells influence each other.
mscan fill each bit in each byte with 1s then check these are set,
fill each bit in each byte with 0s and check these are clear.
prime-0 iterate 8 times by stepping through memory in very large prime
strides clearing just on bit at a time in every byte. Then check
to see if all bits are set to zero.
prime-1 iterate 8 times by stepping through memory in very large prime
strides setting just on bit at a time in every byte. Then check
to see if all bits are set to one.
prime-gray-0 first step through memory in very large prime strides clearing
just on bit (based on a gray code) in every byte. Next, repeat
this but clear the other 7 bits. Then check to see if all bits
are set to zero.
prime-gray-1 first step through memory in very large prime strides setting
just on bit (based on a gray code) in every byte. Next, repeat
this but set the other 7 bits. Then check to see if all bits are
set to one.
rowhammer try to force memory corruption using the rowhammer memory
stressor. This fetches two 32 bit integers from memory and
forces a cache flush on the two addresses multiple times. This
has been known to force bit flipping on some hardware,
especially with lower frequency memory refresh cycles.
walk-0d for each byte in memory, walk through each data line setting
them to low (and the others are set high) and check that the
written value is as expected. This checks if any data lines are
stuck.
walk-1d for each byte in memory, walk through each data line setting
them to high (and the others are set low) and check that the
written value is as expected. This checks if any data lines are
stuck.
walk-0a in the given memory mapping, work through a range of specially
chosen addresses working through address lines to see if any
address lines are stuck low. This works best with physical
memory addressing, however, exercising these virtual addresses
has some value too.
walk-1a in the given memory mapping, work through a range of specially
chosen addresses working through address lines to see if any
address lines are stuck high. This works best with physical
memory addressing, however, exercising these virtual addresses
has some value too.

write64 sequentially write to memory using 32 × 64 bit writes per bogo
loop. Each loop equates to one bogo operation. This exercises
raw memory writes. Note that memory writes are not checked at
the end of each test iteration.
write64nt sequentially write to memory using 32 × 64 bit non-temporal
writes per bogo loop. Each loop equates to one bogo operation.
This exercises cacheless raw memory writes and is only available
on x86 sse2 capable systems built with gcc and clang compilers.
Note that memory writes are not checked at the end of each test
iteration.
write1024v sequentially write to memory using 1 × 1024 bit vector write per
bogo loop (only available if the compiler supports vector
types). Each loop equates to one bogo operation. This
exercises raw memory writes. Note that memory writes are not
checked at the end of each test iteration.
wrrd128nt write to memory in 128 bit chunks using non-temporal writes
(bypassing the cache). Each chunk is written 4 times to hammer
the memory. Then check to see if the data is correct using non-
temporal reads if they are available or normal memory reads if
not. Only available with processors that provide non-temporal
128 bit writes.
zero-one set all memory bits to zero and then check if any bits are not
zero. Next, set all the memory bits to one and check if any bits
are not one.

--vm-ops N
stop vm workers after N bogo operations.

--vm-populate
populate (prefault) page tables for the memory mappings; this can stress
swapping. Only available on systems that support MAP_POPULATE (since Linux
2.5.46).

Virtual memory addressing stressor
--vm-addr N
start N workers that exercise virtual memory addressing using various methods
to walk through a memory mapped address range. This will exercise mapped
private addresses from 8MB to 64MB per worker and try to generate cache and
TLB inefficient addressing patterns. Each method will set the memory to a
random pattern in a write phase and then sanity check this in a read phase.

--vm-addr-method method
specify a vm address stress method. By default, all the stress methods are
exercised sequentially, however one can specify just one method to be used if
required.

Available vm address stress methods are described as follows:

Method Description
all iterate over all the vm stress methods as listed below.
bitposn iteratively write to memory in powers of 2 strides of max_stride to 1
and then read check memory in powers of 2 strides 1 to max_stride
where max_stride is half the size of the memory mapped region. All
bit positions of the memory address space are bit flipped in the
striding.
dec work through the address range backwards sequentially, byte by byte.
decinv like dec, but with all the relevant address bits inverted.
flip address memory using gray coded addresses and their inverse to flip
as many address bits per write/read operation
gray work through memory with gray coded addresses so that each change of
address just changes 1 bit compared to the previous address.
grayinv like gray, but with the all relevant address bits inverted, hence all
bits change apart from 1 in the address range.
inc work through the address range forwards sequentially, byte by byte.
incinv like inc, but with all the relevant address bits inverted.
pwr2 work through memory addresses in steps of powers of two.
pwr2inv like pwr2, but with the all relevant address bits inverted.
rev work through the address range with the bits in the address range
reversed.
revinv like rev, but with all the relevant address bits inverted.

--vm-addr-mlock
attempt to mlock pages into memory causing more memory pressure by preventing
pages from swapped out.

--vm-addr-ops N
stop N workers after N bogo addressing passes.

Memory transfer between parent and child processes stressor (Linux)
--vm-rw N
start N workers that transfer memory to/from a parent/child using
process_vm_writev(2) and process_vm_readv(2). This is feature is only
supported on Linux. Memory transfers are only verified if the --verify option
is enabled.

--vm-rw-bytes N
mmap N bytes per vm-rw worker, the default is 16MB. One can specify the size
as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes
using the suffix b, k, m or g.

--vm-rw-ops N
stop vm-rw workers after N memory read/writes.

Memory unmap from a child process stressor
--vm-segv N
start N workers that create a child process that unmaps its address space
causing a SIGSEGV on return from the unmap.

--vm-segv-ops N
stop after N bogo vm-segv SIGSEGV faults.

Vmsplice stressor (Linux)
--vm-splice N
move data from memory to /dev/null through a pipe without any copying between
kernel address space and user address space using vmsplice(2) and splice(2).
This is only available for Linux.

--vm-splice-bytes N
transfer N bytes per vmsplice call, the default is 64K. One can specify the
size as % of total available memory or in units of Bytes, KBytes, MBytes and
GBytes using the suffix b, k, m or g.

--vm-splice-ops N
stop after N bogo vm-splice operations.

Virtual Memory Area (VMA) stressor
--vma N
start M workers that create pthreads to mmap, munmap, mlock, munlock, madvise,
msync, mprotect, mincore and access 16 pages in a randomly selected virtual
memory address space. This is designed to trip races on VMA page
modifications. Every 15 seconds a different virtual address space is randonly
chosen.

--vma-ops N
stop the vma stressors after N successful memory mappings.

Vector neural network instructions stressor
--vnni N
start N workers that exercise vector neural network instructions (VNNI) used
in convolutional neural network loops. A 256 byte vector is operated upon
using 8 bit multiply with 16 bit summation, 16 bit multiply and 32 bit
summation, and 8 bit summation. When processor features allow, these
operations using 512, 256 and 128 bit vector operations. Generic non-
vectorized code variants also provided (which may be vectorized by more
advanced optimising compilers).

--vnni-intrinsic
just use the vnni methods that use intrinsic VNNI instructions and ignore the
generic non-vectorized methods.

--vnni-method N
select the VNNI method to be exercised, may be one of:

Method Description
all exercise all the following VNNI methods
vpaddb512 8 bit vector addition using 512 bit vector operations on 64 × 8
bit integers, (x86 vpaddb)
vpaddb256 8 bit vector addition using 256 bit vector operations on 32 × 8
bit integers, (x86 vpaddb)
vpaddb128 8 bit vector addition using 128 bit vectors operations on 32 × 8
bit integers, (x86 vpaddb)
vpaddb 8 bit vector addition using 8 bit sequential addition (may be
vectorized by the compiler)
vpdpbusd512 8 bit vector multiplication of unsigned and signed 8 bit values
followed by 16 bit summation using 512 bit vector operations on
64 × 8 bit integers, (x86 vpdpbusd)
vpdpbusd256 8 bit vector multiplication of unsigned and signed 8 bit values
followed by 16 bit summation using 256 bit vector operations on
32 × 8 bit integers, (x86 vpdpbusd)
vpdpbusd128 8 bit vector multiplication of unsigned and signed 8 bit values
followed by 16 bit summation using 128 bit vector operations on
32 × 8 bit integers, (x86 vpdpbusd)
vpdpbusd 8 bit vector multiplication of unsigned and signed 8 bit values
followed by 16 bit summation using sequential operations (may be
vectorized by the compiler)
vpdpwssd512 16 bit vector multiplication of unsigned and signed 16 bit values
followed by 32 bit summation using 512 bit vector operations on
64 × 8 bit integers, (x86 vpdpwssd)
vpdpwssd256 16 bit vector multiplication of unsigned and signed 16 bit values
followed by 32 bit summation using 256 bit vector operations on
64 × 8 bit integers, (x86 vpdpwssd)
vpdpwssd128 16 bit vector multiplication of unsigned and signed 16 bit values
followed by 32 bit summation using 128 bit vector operations on
64 × 8 bit integers, (x86 vpdpwssd)
vpdpwssd 16 bit vector multiplication of unsigned and signed 16 bit values
followed by 32 bit summation using sequential operations (may be
vectorized by the compiler)

--vnni-ops N
stop after N bogo VNNI computation operations. 1 bogo-op is equivalent to 1024
convolution loops operating on 256 bytes of data.

Pausing and resuming threads stressor
--wait N
start N workers that spawn off two children; one spins in a pause(2) loop, the
other continually stops and continues the first. The controlling process waits
on the first child to be resumed by the delivery of SIGCONT using waitpid(2)
and waitid(2).

--wait-ops N
stop after N bogo wait operations.

CPU wait instruction stressor
--waitcpu N
start N workers that exercise processor wait instructions. For x86 these are
pause, tpause and umwait (when available) and nop. For ARM the yield
instruction is used. For other architectures currently nop instructions are
used.

--waitcpu-ops N
stop after N bogo processor wait operations.

Watchdog stressor
--watchdog N
start N workers that exercising the /dev/watchdog watchdog interface by
opening it, perform various watchdog specific ioctl(2) commands on the device
and close it. Before closing the special watchdog magic close message is
written to the device to try and force it to never trip a watchdog reboot
after the stressor has been run. Note that this stressor needs to be run as
root with the --pathological option and is only available on Linux.

--watchdog-ops N
stop after N bogo operations on the watchdog device.

Libc wide characterstring function stressor
--wcs N
start N workers that exercise various libc wide character string functions on
random strings.

--wcs-method wcsfunc
select a specific libc wide character string function to stress. Available
string functions to stress are: all, wcscasecmp, wcscat, wcschr, wcscoll,
wcscmp, wcscpy, wcslen, wcsncasecmp, wcsncat, wcsncmp, wcsrchr and wcsxfrm.
The 'all' method is the default and will exercise all the string methods.

--wcs-ops N
stop after N bogo wide character string operations.

scheduler workload stressor
--workload N
start N workers that exercise the scheduler with items of work that are
started at random times with random sleep delays between work items. By
default a 100,000 microsecond slice of time has 100 work items that start at
random times during the slice. The work items by default run for a quanta of
1000 microseconds scaled by the percentage work load (default of 30%). For a
slice of S microseconds and a work item quanta duration of Q microseconds, S /
Q work items are executed per slice. For a work load of L percent, the run
time per item is the quanta Q × L / 100 microseconds. The --workload-hreads
option allows work items to be taken from a queue and run concurrently if the
scheduling run times overlap.
If a work item is already running when a new work item is scheduled to run
then the new work item is delayed and starts directly after the completion of
the currently running work item when running with the default of zero worker
threads. This emulates bursty scheduled compute, such as handling input
packets where one may have lots of work items bunched together or with random
unpredictable delays between work items.

--workload-load L
specify the percentage run time load of each work item with respect to the run
quanta duration. Essentially the run duration of each work item is the quanta
duration Q × L / 100.

--workload-method method
select the workload method. Each quanta of execution time is consumed using a
tight spin-loop executing a workload method. The available methods are
described as follows:

Method Description
all randomly select any one of all the following methods:
fma perform multiply-add operations, on modern processors
these may be compiled into fused-multiply-add
instructions.
getpid get the stressor's PID via getpid(2).
time get the current time via time(2).
inc64 increment a 64 bit integer.
memmove copy (move) a 1MB buffer using memmove(3).
memread read from a 1MB buffer using fast memory reads.
memset write to a 1MB buffer using memset(3).
mcw64 compute 64 bit random numbers using a mwc random
generator.
nop waste cycles using no-op instructions.
pause stop execution using CPU pause/yield or memory barrier
instructions where available.
random a random mix of all the workload methods, changing the
workload method on every spin-loop.
sqrt perform double precision floating point sqrt(3) and
hypot(3) math operations.

--workload-slice-us S
specify the duration of each scheduling slice in microseconds. The default is
100,000 microseconds (0.1 seconds).

--workload-quanta-us Q
specify the duration of each work item in microseconds. The default is 1000
microseconds (1 millisecond).

--workload-threads N
use N process threads to take scheduler work items of a workqueue and run the
work item. When N is 0 (default), no threads are used and the work items are
run back-to-back sequentially without using work queue. Using more than 2
threads allows work items to be handled concurrently if enough idle processors
are available.

Method Description
cluster cluster 2/3 of the start times to try to start at the random time
during the time slice, with the other 1/3 of start times evenly
randomly distributed using a single random variable. The clustered
start times causes a burst of items to be scheduled in a bunch with
no delays between each clustered work item.
even evenly distribute scheduling start times across the workload slice
poisson generate scheduling events that occur individually at random moments,
but which tend to occur at an average rate (known as a Poisson
process).
random1 evenly randomly distribute scheduling start times using a single
random variable.
random2 randomly distribute scheduling start times using a sum of two random
variables, much like throwing 2 dice.
random3 randomly distribute scheduling start times using a sum of three
random variables, much like throwing 3 dice.

--workload-ops N
stop the workload workers after N workload bogo-operations.

x86 cpuid stressor
--x86cpuid N
start N workers that exercise the x86 cpuid instruction with 18 different leaf
types.

--x86cpuid-ops N
stop after N iterations that exercise the different cpuid leaf types.

x86-64 syscall stressor (Linux)
--x86syscall N
start N workers that repeatedly exercise the x86-64 syscall instruction to
call the getcpu(2), geteuid(2), getgid(2), getpid(2), gettimeofday(2) and
time(2) system calls using the Linux vsyscall handler. Only for Linux.

--x86syscall-func F
Instead of exercising the 6 syscall system calls, just call the syscall
function F. The function F must be one of getcpu, geteuid, getgid, getpid,
gettimeofday or time.

--x86syscall-ops N
stop after N x86syscall system calls.

Extended file attributes stressor
--xattr N
start N workers that create, update and delete batches of extended attributes
on a file.

--xattr-ops N
stop after N bogo extended attribute operations.

Yield scheduling stressor
-y N, --yield N
start N workers that call sched_yield(2). This stressor ensures that at least
2 child processes per CPU exercise shield_yield(2) no matter how many workers
are specified, thus always ensuring rapid context switching.

--yield-ops N
stop yield stress workers after N sched_yield(2) bogo operations.

/dev/zero stressor
--zero N
start N workers that exercise /dev/zero with reads, lseeks, ioctls and mmaps.
For just /dev/zero read benchmarking use the --zero-read option.

--zero-ops N
stop zero stress workers after N /dev/zero bogo read operations.

--zero-read
just read /dev/zero with 4K reads with no additional exercising on /dev/zero.

Zlib stressor
--zlib N
start N workers compressing and decompressing random data using zlib. Each
worker has two processes, one that compresses random data and pipes it to
another process that decompresses the data. This stressor exercises CPU, cache
and memory.

--zlib-level L
specify the compression level (0..9), where 0 = no compression, 1 = fastest
compression and 9 = best compression.

--zlib-mem-level L
specify the reserved compression state memory for zlib. Default is 8.

Value
1 minimum memory usage.
9 maximum memory usage.

--zlib-method method
specify the type of random data to send to the zlib library. By default, the
data stream is created from a random selection of the different data
generation processes. However one can specify just one method to be used if
required. Available zlib data generation methods are described as follows:

Method Description
00ff randomly distributed 0x00 and 0xFF values.
ascii01 randomly distributed ASCII 0 and 1 characters.
asciidigits randomly distributed ASCII digits in the range of 0 and 9.
bcd packed binary coded decimals, 0..99 packed into 2 4-bit nybbles.
binary 32 bit random numbers.
brown 8 bit brown noise (Brownian motion/Random Walk noise).
double double precision floating point numbers from sin(θ).
fixed data stream is repeated 0x04030201.
gcr random values as 4 × 4 bit data turned into 4 × 5 bit group coded
recording (GCR) patterns. Each 5 bit GCR value starts or ends
with at most one zero bit so that concatenated GCR codes have no
more than two zero bits in a row.
gray 16 bit gray codes generated from an incrementing counter.
inc16 16 bit incrementing values starting from a random 16 bit value.
latin Random latin sentences from a sample of Lorem Ipsum text.
lehmer Fast random values generated using Lehmer's generator using a 128
bit multiply.
lfsr32 Values generated from a 32 bit Galois linear feedback shift
register using the polynomial x↑32 + x↑31 + x↑29 + x + 1. This
generates a ring of 2↑32 - 1 unique values (all 32 bit values
except for 0).
logmap Values generated from a logistical map of the equation Χn+1 = r ×
Χn × (1 - Χn) where r > ≈ 3.56994567 to produce chaotic data. The
values are scaled by a large arbitrary value and the lower 8 bits
of this value are compressed.
lrand48 Uniformly distributed pseudo-random 32 bit values generated from
lrand48(3).
morse Morse code generated from random latin sentences from a sample of
Lorem Ipsum text.
nybble randomly distributed bytes in the range of 0x00 to 0x0f.
objcode object code selected from a random start point in the stress-ng
text segment.
parity 7 bit binary data with 1 parity bit.
pink pink noise in the range 0..255 generated using the Gardner method
with the McCartney selection tree optimization. Pink noise is
where the power spectral density is inversely proportional to the
frequency of the signal and hence is slightly compressible.
random segments of the data stream are created by randomly calling the
different data generation methods.
rarely1 data that has a single 1 in every 32 bits, randomly located.
rarely0 data that has a single 0 in every 32 bits, randomly located.
rdrand generate random data using rdrand instruction (x86) or use 64 bit
mwc psuedo-random number generator for non-x86 systems.
ror32 generate a 32 bit random value, rotate it right 0 to 7 places and
store the rotated value for each of the rotations.
text random ASCII text.
utf8 random 8 bit data encoded to UTF-8.
zero all zeros, compresses very easily.

--zlib-ops N
stop after N bogo compression operations, each bogo compression operation is a
compression of 64K of random data at the highest compression level.

--zlib-strategy S
specifies the strategy to use when deflating data. This is used to tune the
compression algorithm. Default is 0.

Value
0 used for normal data (Z_DEFAULT_STRATEGY).
1 for data generated by a filter or predictor (Z_FILTERED)
2 forces huffman encoding (Z_HUFFMAN_ONLY).
3 Limit match distances to one run-length-encoding (Z_RLE).
4 prevents dynamic huffman codes (Z_FIXED).

--zlib-stream-bytes S
specify the amount of bytes to deflate until deflate should finish the block
and return with Z_STREAM_END. One can specify the size in units of Bytes,
KBytes, MBytes and GBytes using the suffix b, k, m or g. Default is 0 which
creates and endless stream until stressor ends.

Value
0 creates an endless deflate stream until stressor stops.

n creates an stream of n bytes over and over again.
Each block will be closed with Z_STREAM_END.

--zlib-window-bits W
specify the window bits used to specify the history buffer size. The value is
specified as the base two logarithm of the buffer size (e.g. value 9 is 2↑9 =
512 bytes). Default is 15.

Value
-8-(-15) raw deflate format.
8-15 zlib format.
24-31 gzip format.
40-47 inflate auto format detection using zlib deflate format.

Zombie processes stressor
--zombie N
start N workers that create zombie processes. This will rapidly try to create
a default of 8192 child processes that immediately die and wait in a zombie
state until they are reaped. Once the maximum number of processes is reached
(or fork fails because one has reached the maximum allowed number of children)
the oldest child is reaped and a new process is then created in a first-in
first-out manner, and then repeated.

--zombie-max N
try to create as many as N zombie processes. This may not be reached if the
system limit is less than N.

--zombie-ops N
stop zombie stress workers after N bogo zombie operations.

EXAMPLES

       stress-ng --vm 8 --vm-bytes 80% -t 1h

              run 8 virtual memory stressors that combined use 80% of the available memory for  1
              hour. Thus each stressor uses 10% of the available memory.

       stress-ng --cpu 4 --io 2 --vm 1 --vm-bytes 1G --timeout 60s

              runs  for  60  seconds with 4 cpu stressors, 2 io stressors and 1 vm stressor using
              1GB of virtual memory.

       stress-ng --iomix 2 --iomix-bytes 10% -t 10m

              runs 2 instances of the mixed I/O stressors using a total of 10% of  the  available
              file  system  space for 10 minutes. Each stressor will use 5% of the available file
              system space.

       stress-ng --with cpu,matrix,vecmath,fp --seq 8 -t 1m

              run 8 instances of cpu, matrix, vecmath and fp  stressors  sequentially  one  after
              another, for 1 minute per stressor.

       stress-ng --with cpu,matrix,vecmath,fp --permute 5 -t 10s

              run  permutations  of  5  instances  of  cpu,  matrix,  vecmath  and  fp  stressors
              sequentially one after another, for 10 seconds per permutation mix.

       stress-ng  --cyclic  1  --cyclic-dist  2500  --cyclic-method  clock_ns  --cyclic-prio  100
       --cyclic-sleep 10000 --hdd 0 -t 1m

              measures  real time scheduling latencies created by the hdd stressor. This uses the
              high resolution nanosecond clock to  measure  latencies  during  sleeps  of  10,000
              nanoseconds.  At  the  end  of 1 minute of stressing, the latency distribution with
              2500 ns intervals will be displayed. NOTE: this must be run with  the  CAP_SYS_NICE
              capability to enable the real time scheduling to get accurate measurements.

       stress-ng --cpu 8 --cpu-ops 800000

              runs 8 cpu stressors and stops after 800000 bogo operations.

       stress-ng --sequential 2 --timeout 2m --metrics

              run 2 simultaneous instances of all the stressors sequentially one by one, each for
              2 minutes and summarise with performance metrics at the end.

       stress-ng --cpu 4 --cpu-method fft --cpu-ops 10000 --metrics-brief

              run 4 FFT cpu stressors, stop after 10000 bogo operations  and  produce  a  summary
              just for the FFT results.

       stress-ng --cpu -1 --cpu-method all -t 1h --cpu-load 90

              run  cpu  stressors  on  all  online  CPUs  working  through  all the available CPU
              stressors for 1 hour, loading the CPUs at 90% load capacity.

       stress-ng --cpu 0 --cpu-method all -t 20m

              run cpu stressors on all configured CPUs working  through  all  the  available  CPU
              stressors for 20 minutes

       stress-ng --all 4 --timeout 5m

              run 4 instances of all the stressors for 5 minutes.

       stress-ng --random 64

              run 64 stressors that are randomly chosen from all the available stressors.

       stress-ng --cpu 64 --cpu-method all --verify -t 10m --metrics-brief

              run  64  instances  of  all  the  different  cpu  stressors  and  verify  that  the
              computations are correct for 10 minutes with a bogo operations summary at the end.

       stress-ng --sequential -1 -t 10m

              run all the stressors one by one for 10 minutes, with the number  of  instances  of
              each stressor matching the number of online CPUs.

       stress-ng --sequential 8 --class io -t 5m --times

              run  all  the  stressors  in  the  io  class  one by one for 5 minutes each, with 8
              instances of each stressor running concurrently and show overall  time  utilisation
              statistics at the end of the run.

       stress-ng --all -1 --maximize --aggressive

              run  all the stressors (1 instance of each per online CPU) simultaneously, maximize
              the  settings  (memory  sizes,  file  allocations,  etc.)  and  select   the   most
              demanding/aggressive options.

       stress-ng --random 32 -x numa,hdd,key

              run 32 randomly selected stressors and exclude the numa, hdd and key stressors

       stress-ng --sequential 4 --class vm --exclude bigheap,brk,stack

              run  4  instances  of the VM stressors one after each other, excluding the bigheap,
              brk and stack stressors

       stress-ng --taskset 0,2-3 --cpu 3

              run 3 instances of the CPU stressor and pin them to CPUs 0, 2 and 3.

EXIT STATUS

         Status     Description
           0        Success.
           1        Error; incorrect user options or a fatal  resource  issue  in  the  stress-ng
                    stressor harness (for example, out of memory).
           2        One or more stressors failed.
           3        One  or more stressors failed to initialise because of lack of resources, for
                    example ENOMEM (no memory), ENOSPC (no space on file system) or a missing  or
                    unimplemented system call.
           4        One  or  more  stressors  were  not implemented on a specific architecture or
                    operating system.
           5        A stressor has been killed by an unexpected signal.
           6        A stressor exited by exit(2) which was not expected and timing metrics  could
                    not be gathered.
           7        The bogo ops metrics maybe untrustworthy. This is most likely to occur when a
                    stress test is terminated during the update of a  bogo-ops  counter  such  as
                    when  it  has been OOM killed. A less likely reason is that the counter ready
                    indicator has been corrupted.

BUGS

       File bug reports at: https://github.com/ColinIanKing/stress-ng/issues

AUTHOR

       stress-ng was written by Colin Ian King <colin.i.king@gmail.com> and is a clean  room  re-
       implementation and extension of the original stress tool by Amos Waterland. Thanks also to
       the many contributors to stress-ng. The README.md file in the source contains a full  list
       of the contributors.

NOTES

       Sending  a  SIGALRM, SIGINT or SIGHUP to stress-ng causes it to terminate all the stressor
       processes and ensures temporary files and shared memory segments are removed cleanly.

       Sending a SIGUSR2 to  stress-ng  will  dump  out  the  current  load  average  and  memory
       statistics.

       Note  that  the  stress-ng  cpu, io, vm and hdd tests are different implementations of the
       original stress tests and hence may produce different stress characteristics.

       The bogo operations metrics may change with each release  because  of  bug  fixes  to  the
       code,  new  features,  compiler optimisations, changes in support libraries or system call
       performance.

COPYRIGHT

       Copyright © 2013-2021 Canonical Ltd, Copyright © 2021-2024 Colin Ian King.
       This is free software; see the source for copying conditions.  There is NO  warranty;  not
       even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

                                         26 February 2024                            STRESS-NG(1)