Ubuntu Manpage: stress-ng - a tool to load and stress a computer system

Provided by: stress-ng_0.13.12-2ubuntu1_amd64

NAME

       stress-ng - 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.

--class name
specify the class of stressors to run. Stressors are classified into one or more of
the following classes: cpu, cpu-cache, device, io, interrupt, filesystem, memory,
network, os, pipe, scheduler 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.

-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.

--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.

--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.

--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.

--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. The metrics are just a useful way
to observe 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.
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 total bogo operations per second based on
time) 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%.

--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.

--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 quickly
consume resources in such a way that they can rapidly hang a system before the
kernel can OOM kill them. These stressors are not enabled by default, this option
enables them, but you probably don't want to do this. You have been warned.

--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.

-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.

--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.

--stdout
all output goes to stdout. By default all output goes to stderr (which is a
historical oversight that will cause breakage to users if it is now changed). This
option allows the output to be written to stdout.

--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), 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 a non-interritable 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.

--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.

--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.

--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. Currently a Linux only option.

-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 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.

--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-ops N
stop affinity workers after N bogo affinity operations. Note that the counters
across the 16 processes are not locked to improve affinity test rates so the final
number of bogo-ops will be equal or more than the specified ops stop threshold
because of racy unlocked bogo-op counting.

--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-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.

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

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

--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.

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

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

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

--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 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.

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

--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 real physical memory.

--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-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.

-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.

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

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

--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.

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

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

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

--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 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 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 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 50000ns 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 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-ops N
stop clone stress workers after N bogo clone operations.

--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.

--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.

--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 N
start N stressors that copy a file using the Linux copy_file_range(2) system call.
2MB 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-ops N
stop after N copy_file_range() calls.

--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.

-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.

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

-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
cpuid fetch cpu specific information using the cpuid
instruction (x86 only)
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
div16 50,000 16 bit unsigned integer divisions
div32 50,000 32 bit unsigned integer divisions
div64 50,000 64 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 naive 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-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-all
The default is to never offline the first CPU. This option will offline and online
all the CPUs include CPU 0. This may cause some systems to shutdown.

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

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

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

--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. 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-ops N
stop after N sleeps.

--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-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-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 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.

--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-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.

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

--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-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.

--dir N
start N workers that create and remove directories using mkdir and rmdir.

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

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

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

--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-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.

--dirmany N
start N stressors that create as many empty 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 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-ops N
stop dirmany stressors after N empty files have been created.

--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 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.

--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.

--efivar N
start N works that exercise the Linux /sys/firmware/efi/vars interface by reading
the EFI variables. This is a Linux only stress test for platforms that support the
EFI vars interface and requires the CAP_SYS_ADMIN capability.

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

--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

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

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

--eventfd-nonblock N
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.

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

--exec-max P
create P child processes that exec stress-ng 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 --exec-max and --exec.

--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.

-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.

--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.

--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 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.

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

--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.

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

--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.

--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 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 /

--flock N
start N workers locking on a single file.

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

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

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

--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-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.

--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.

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

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

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

--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.

--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.

--funccall N
start N workers that call functions of 1 through to 9 arguments. By default
functions with uint64_t arguments are called, however, this can be changed using
the --funccall-method option.

--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 uint64_t
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.

--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.

--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.

--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.

--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.

--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.

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

--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.

--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.

--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-ops N
stop after N hashing rounds

--hash-method M
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
mulxror64 64 bit multiply, xor and rotate right. Mangles
64 bits where possible. Designed by Colin Ian
King
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
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
xxhash the "Extremely fast" hash in non-streaming mode

-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.

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

--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).

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

--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.

--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-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.

--icache N
start N workers that stress the instruction cache by forcing instruction cache
reloads. This is achieved by modifying an instruction cache line, causing the
processor to reload it when we call a function in inside it. Currently only
verified and enabled for Intel x86 CPUs.

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

--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-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-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 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.

-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 options.

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

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

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

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

--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.

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

--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-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.

--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 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.

--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.

--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.

--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 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.

--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-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 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.

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

--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.

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

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

--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.

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

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

--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.

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

--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.

--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.

--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).

--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.

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

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

--malloc N
start N workers continuously calling malloc(3), calloc(3), realloc(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 malloc, calloc or
realloc) 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-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.

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

--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-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.

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

--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-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.

--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.

--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.

--memcpy N
start N workers that copy 2MB of data from a shared region to a buffer using
memcpy(3) and then move the data in the buffer with memmove(3) with 3 different
alignments. This will exercise processor cache and system memory.

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

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

Method Description
all use libc, builtin and naive 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 naive byte by byte copying and memory moving build
with default compiler optimization flags
naive_o0 use unoptimized naive byte by byte copying and memory
moving

naive_o3 use optimized naive byte by byte copying and memory moving
build with -O3 optimization and where possible use CPU
specific optimizations

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

--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.

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

--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.

--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.

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

--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
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
mfence stores with write serialization
prefetch prefetch data at random memory locations
random randomly run any of the memthrash methods except for
'random' and 'all'
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

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

--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).

--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 N
start N workers that perform misaligned read and writes. By default, this will
exercise 128 bit misaligned read and writes in 8 x 16 bits, 4 x 32 bits, 2 x 64
bits and 1 x 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-ops N
stop after N misaligned bogo operation. A misaligned bogo op is equivalent to 65536
x 128 bit reads or writes.

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

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

--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.

--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.

--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.

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

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

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

--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.

--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 to an address
that is several pages higher in memory. Mappings and remappings are madvised with
random madvise options to further exercise the mappings.

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

--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-ops N
stop after N mmaphuge bogo operations

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

--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-ops N
stop after N mmapmany bogo operations

--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.

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

--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 remapped pages into memory prohibiting them from being paged out.
This is a no-op if mlock(2) is not available.

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

--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.

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

--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.

--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.

--nanosleep N
start N workers that each run 256 pthreads that call nanosleep with random delays
from 1 to 2^18 nanoseconds. This should exercise the high resolution timers and
scheduler.

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

--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-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 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

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

--nop-instr INSTR
use alternative nop instruction INSTR. For x86 CPUs INSTR can be one of nop, pause,
nop2 (2 byte nop) through to nop11 (11 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.

--null N
start N workers writing to /dev/null.

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

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

--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.

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

--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.

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

--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.

--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 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 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.

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

--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.

--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.

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

--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-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. Default size is 512 bytes.

--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.

--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.

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

--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.

--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

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

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

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

--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.

--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.

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

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

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

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

--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 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.

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

--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).

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

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

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

--rawdev-method M
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.

--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.

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

--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-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.

--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.

--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.

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

--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.

--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).

--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 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.

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

-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.

--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.

--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-ops N
stop after N resource child forks.

--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.

--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.

--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.

--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 mistmatch
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.

--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.

--schedpolicy N
start N workers that work 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.

--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-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.

--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.

--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.

--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.

--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.

--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.

--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 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.

--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.

--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 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).

--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-ops N
stop after N POSIX shared memory create and destroy bogo operations are complete.

--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-objs N
specify the number of shared memory objects to be created.

--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-ops N
stop after N shared memory create and destroy bogo operations are complete.

--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-segs N
specify the number of shared memory segments to be created. The default is 8
segments.

--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.

--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 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 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 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.

--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.

--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.

--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 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.

--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.

--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.

--sigsegv N
start N workers that rapidly create and catch segmentation faults.

--sigsegv-ops N
stop sigsegv stress workers after N bogo segmentation faults.

--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 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.

--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.

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

--sleep-max P
start P threads per worker. The default is 1024, the maximum allowed is 30000.

--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 naive benchmarking.

--smi-ops N
stop after N attempts to trigger the SMI.

-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-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-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-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 thse 3 on each iteration. Note that sendmmsg is only available for Linux
systems that support this system call.

--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.

--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.

--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.

--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.

--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-ops N
stop after N connections.

--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 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.

--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 x 500 sparse matrix is used and 5000 items are put
into the sparse matrix making it 2% utilized.

--sparsematrix-ops N
stop after N sparsematrix test iterations.

--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.

--sparsematrix-size N
use a N × N sized 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
each unique value 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 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.

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

--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.

--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 prohibiting them from being paged out.
This is a no-op if mlock(2) is not available.

--stack-ops N
stop stack stress workers after N bogo stack overflows.

--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.

--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 N
start N workers exercising a memory bandwidth stressor 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.

--stream-ops N
stop after N stream bogo operations, where a bogo operation is one round of copy,
scale, add and triad operations.

--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-madvise [ 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'.

--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.

-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-ops N
stop context switching workers after N bogo operations.

--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.

--symlink N
start N workers creating and removing symbolic links.

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

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

--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.

--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-ops N
stop syncload workers after N load/sleep cycles.

--syncload-msbusy M
specify the busy load duration in milliseconds.

--syncload-mssleep M
specify the sleep duration in milliseconds.

--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.

--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.

--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.

--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.

--sys-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 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.

-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-ops N
stop timer stress workers after N bogo timer events (Linux only).

--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-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 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.

--timerfd-ops N
stop timerfd stress workers after N bogo timerfd events (Linux only).

--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-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.

--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 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-ops N
stop tmpfs stressors after N bogo mmap operations.

--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.

--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) 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.

--tree-method [ all | avl | binary | rb | splay ]
specify the tree to be used. By default, both the rb ad splay trees are used (the
'all' option).

--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 and the rdcycle instruction for RISC-V.

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

--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.

--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 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, ipv6 and unix are
supported.

--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-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-ops N
stop udp-flood stress workers after N bogo operations.

--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 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.

-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).

--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-ops N
stop userfaultfd stress workers after N page faults.

--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.

--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.

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

--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.

--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-ops N
stop after N vDSO functions calls.

--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.

--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.

--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).

--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 N
start N workers continually vforking children that immediately exit.

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

--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-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 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.

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

--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 m
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.
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.
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.
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 x 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 x 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 x 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 x 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.
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-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).

--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-ops N
stop N workers after N bogo addressing passes.

--vm-addr-method M
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.
pwr2 work through memory addresses in steps of powers of two.
pwr2inv like pwr2, but with the all relevant address bits
inverted.
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.
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.
inc work through the address range forwards sequentially, byte
by byte.
incinv like inc, but with all the relevant address bits inverted.
dec work through the address range backwards sequentially,
byte by byte.
decinv like dec, but with all the relevant address bits inverted.

--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-ops N
stop vm-rw workers after N memory read/writes.

--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-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.

--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-ops N
stop after N bogo vm-splice operations.

--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.

--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.

--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.

--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.

--x86syscall N
start N workers that repeatedly exercise the x86-64 syscall instruction to call the
getcpu(2), gettimeofday(2) and time(2) system using the Linux vsyscall handler.
Only for Linux.

--x86syscall-ops N
stop after N x86syscall system calls.

--x86syscall-func F
Instead of exercising the 3 syscall system calls, just call the syscall function F.
The function F must be one of getcpu, gettimeofday and time.

--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.

-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.

--zero N
start N workers reading /dev/zero.

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

--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-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-level L
specify the compression level (0..9), where 0 = no compression, 1 = fastest
compression and 9 = best compression.

--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.

gray 16 bit gray codes generated from an incrementing counter.
latin Random latin sentences from a sample of Lorem Ipsum text.
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.
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).
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.
text random ASCII text.
utf8 random 8 bit data encoded to UTF-8.
zero all zeros, compresses very easily.

--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.

Values:
-8-(-15): raw deflate format
8-15: zlib format
24-31: gzip format
40-47: inflate auto format detection using zlib deflate format

--zlib-mem-level L specify the reserved compression state memory for zlib. Default is 8.

Values:
1 = minimum memory usage
9 = maximum memory usage

--zlib-strategy S
specifies the strategy to use when deflating data. This is used to tune the
compression algorithm. Default is 0.

Values:
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.

Values:
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.

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

--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.

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  --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
       for  contributions  from  Abdul  Haleem,  Aboorva  Devarajan,  Adrian  Ratiu,  André Wild,
       Alexander Kanavin, Baruch Siach, Carlos  Santos  Christian  Ehrhardt,  Chunyu  Hu,  Danilo
       Krummrich,  David  Turner,  Dominik  B  Czarnota,  Fabien Malfoy, Fabrice Fontaine, Helmut
       Grohne, James Hunt, James Wang, Jianshen Liu, Jim Rowan, John Kacur,  Joseph  DeVincentis,
       Jules  Maselbas,  Khalid Elmously, Khem Raj, Luca Pizzamiglio, Luis Henriques, Manoj Iyer,
       Matthew Tippett, Mauricio  Faria  de  Oliveira,  Maxime  Chevallier,  Piyush  Goyal,  Ralf
       Ramsauer,  Rob  Colclaser,  Thadeu  Lima  de  Souza Cascardo, Thia Wyrod, Tim Gardner, Tim
       Orling, Tommi Rantala, Witold Baryluk, Zhiyi Sun and others.

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.  stress-ng
       does not support any GPU stress tests.

       The bogo operations metrics may change with each release  because  of  bug  fixes  to  the
       code, new features, compiler optimisations or changes in system call performance.

COPYRIGHT

       Copyright © 2013-2021 Canonical Ltd, Copyright © 2021 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.

                                           6 March 2022                              STRESS-NG(1)