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NAME
proc - process information pseudo-filesystem
DESCRIPTION
The proc filesystem is a pseudo-filesystem which provides an interface to kernel data
structures. It is commonly mounted at /proc. Most of it is read-only, but some files
allow kernel variables to be changed.
Mount options
The proc filesystem supports the following mount options:
hidepid=n (since Linux 3.3)
This option controls who can access the information in /proc/[pid] directories.
The argument, n, is one of the following values:
0 Everybody may access all /proc/[pid] directories. This is the traditional
behavior, and the default if this mount option is not specified.
1 Users may not access files and subdirectories inside any /proc/[pid]
directories but their own (the /proc/[pid] directories themselves remain
visible). Sensitive files such as /proc/[pid]/cmdline and /proc/[pid]/status
are now protected against other users. This makes it impossible to learn
whether any user is running a specific program (so long as the program doesn't
otherwise reveal itself by its behavior).
2 As for mode 1, but in addition the /proc/[pid] directories belonging to other
users become invisible. This means that /proc/[pid] entries can no longer be
used to discover the PIDs on the system. This doesn't hide the fact that a
process with a specific PID value exists (it can be learned by other means, for
example, by "kill -0 $PID"), but it hides a process's UID and GID, which could
otherwise be learned by employing stat(2) on a /proc/[pid] directory. This
greatly complicates an attacker's task of gathering information about running
processes (e.g., discovering whether some daemon is running with elevated
privileges, whether another user is running some sensitive program, whether
other users are running any program at all, and so on).
gid=gid (since Linux 3.3)
Specifies the ID of a group whose members are authorized to learn process
information otherwise prohibited by hidepid (ie/e/, users in this group behave as
though /proc was mounted with hidepid=0. This group should be used instead of
approaches such as putting nonroot users into the sudoers(5) file.
Files and directories
The following list describes many of the files and directories under the /proc hierarchy.
/proc/[pid]
There is a numerical subdirectory for each running process; the subdirectory is
named by the process ID. Each such subdirectory contains the following pseudo-
files and directories.
/proc/[pid]/attr
The files in this directory provide an API for security modules. The contents of
this directory are files that can be read and written in order to set security-
related attributes. This directory was added to support SELinux, but the intention
was that the API be general enough to support other security modules. For the
purpose of explanation, examples of how SELinux uses these files are provided
below.
This directory is present only if the kernel was configured with CONFIG_SECURITY.
/proc/[pid]/attr/current (since Linux 2.6.0)
The contents of this file represent the current security attributes of the process.
In SELinux, this file is used to get the security context of a process. Prior to
Linux 2.6.11, this file could not be used to set the security context (a write was
always denied), since SELinux limited process security transitions to execve(2)
(see the description of /proc/[pid]/attr/exec, below). Since Linux 2.6.11, SELinux
lifted this restriction and began supporting "set" operations via writes to this
node if authorized by policy, although use of this operation is only suitable for
applications that are trusted to maintain any desired separation between the old
and new security contexts. Prior to Linux 2.6.28, SELinux did not allow threads
within a multi-threaded process to set their security context via this node as it
would yield an inconsistency among the security contexts of the threads sharing the
same memory space. Since Linux 2.6.28, SELinux lifted this restriction and began
supporting "set" operations for threads within a multithreaded process if the new
security context is bounded by the old security context, where the bounded relation
is defined in policy and guarantees that the new security context has a subset of
the permissions of the old security context. Other security modules may choose to
support "set" operations via writes to this node.
/proc/[pid]/attr/exec (since Linux 2.6.0)
This file represents the attributes to assign to the process upon a subsequent
execve(2).
In SELinux, this is needed to support role/domain transitions, and execve(2) is the
preferred point to make such transitions because it offers better control over the
initialization of the process in the new security label and the inheritance of
state. In SELinux, this attribute is reset on execve(2) so that the new program
reverts to the default behavior for any execve(2) calls that it may make. In
SELinux, a process can set only its own /proc/[pid]/attr/exec attribute.
/proc/[pid]/attr/fscreate (since Linux 2.6.0)
This file represents the attributes to assign to files created by subsequent calls
to open(2), mkdir(2), symlink(2), and mknod(2)
SELinux employs this file to support creation of a file (using the aforementioned
system calls) in a secure state, so that there is no risk of inappropriate access
being obtained between the time of creation and the time that attributes are set.
In SELinux, this attribute is reset on execve(2), so that the new program reverts
to the default behavior for any file creation calls it may make, but the attribute
will persist across multiple file creation calls within a program unless it is
explicitly reset. In SELinux, a process can set only its own
/proc/[pid]/attr/fscreate attribute.
/proc/[pid]/attr/prev (since Linux 2.6.0)
This file contains the security context of the process before the last execve(2);
that is, the previous value of /proc/[pid]/attr/current.
/proc/[pid]/attr/keycreate (since Linux 2.6.18)
If a process writes a security context into this file, all subsequently created
keys (add_key(2)) will be labeled with this context. For further information, see
the kernel source file Documentation/keys.txt.
/proc/[pid]/attr/socketcreate (since Linux 2.6.18)
If a process writes a security context into this file, all subsequently created
sockets will be labeled with this context.
/proc/[pid]/auxv (since 2.6.0-test7)
This contains the contents of the ELF interpreter information passed to the process
at exec time. The format is one unsigned long ID plus one unsigned long value for
each entry. The last entry contains two zeros. See also getauxval(3).
/proc/[pid]/cgroup (since Linux 2.6.24)
This file describes control groups to which the process/task belongs. For each
cgroup hierarchy there is one entry containing colon-separated fields of the form:
5:cpuacct,cpu,cpuset:/daemons
The colon-separated fields are, from left to right:
1. hierarchy ID number
2. set of subsystems bound to the hierarchy
3. control group in the hierarchy to which the process belongs
This file is present only if the CONFIG_CGROUPS kernel configuration option is
enabled.
/proc/[pid]/clear_refs (since Linux 2.6.22)
This is a write-only file, writable only by owner of the process.
The following values may be written to the file:
1 (since Linux 2.6.22)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all the pages associated
with the process. (Before kernel 2.6.32, writing any nonzero value to this
file had this effect.)
2 (since Linux 2.6.32)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all anonymous pages
associated with the process.
3 (since Linux 2.6.32)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all file-mapped pages
associated with the process.
Clearing the PG_Referenced and ACCESSED/YOUNG bits provides a method to measure
approximately how much memory a process is using. One first inspects the values in
the "Referenced" fields for the VMAs shown in /proc/[pid]/smaps to get an idea of
the memory footprint of the process. One then clears the PG_Referenced and
ACCESSED/YOUNG bits and, after some measured time interval, once again inspects the
values in the "Referenced" fields to get an idea of the change in memory footprint
of the process during the measured interval. If one is interested only in
inspecting the selected mapping types, then the value 2 or 3 can be used instead of
1.
A further value can be written to affect a different bit:
4 (since Linux 3.11)
Clear the soft-dirty bit for all the pages associated with the process.
This is used (in conjunction with /proc/[pid]/pagemap) by the check-point
restore system to discover which pages of a process have been dirtied since
the file /proc/[pid]/clear_refs was written to.
Writing any value to /proc/[pid]/clear_refs other than those listed above has no
effect.
The /proc/[pid]/clear_refs file is present only if the CONFIG_PROC_PAGE_MONITOR
kernel configuration option is enabled.
/proc/[pid]/cmdline
This read-only file holds the complete command line for the process, unless the
process is a zombie. In the latter case, there is nothing in this file: that is, a
read on this file will return 0 characters. The command-line arguments appear in
this file as a set of strings separated by null bytes ('\0'), with a further null
byte after the last string.
/proc/[pid]/comm (since Linux 2.6.33)
This file exposes the process's comm value—that is, the command name associated
with the process. Different threads in the same process may have different comm
values, accessible via /proc/[pid]/task/[tid]/comm. A thread may modify its comm
value, or that of any of other thread in the same thread group (see the discussion
of CLONE_THREAD in clone(2)), by writing to the file /proc/self/task/[tid]/comm.
Strings longer than TASK_COMM_LEN (16) characters are silently truncated.
This file provides a superset of the prctl(2) PR_SET_NAME and PR_GET_NAME
operations, and is employed by pthread_setname_np(3) when used to rename threads
other than the caller.
/proc/[pid]/coredump_filter (since Linux 2.6.23)
See core(5).
/proc/[pid]/cpuset (since Linux 2.6.12)
See cpuset(7).
/proc/[pid]/cwd
This is a symbolic link to the current working directory of the process. To find
out the current working directory of process 20, for instance, you can do this:
$ cd /proc/20/cwd; /bin/pwd
Note that the pwd command is often a shell built-in, and might not work properly.
In bash(1), you may use pwd -P.
In a multithreaded process, the contents of this symbolic link are not available if
the main thread has already terminated (typically by calling pthread_exit(3)).
/proc/[pid]/environ
This file contains the environment for the process. The entries are separated by
null bytes ('\0'), and there may be a null byte at the end. Thus, to print out the
environment of process 1, you would do:
$ strings /proc/1/environ
/proc/[pid]/exe
Under Linux 2.2 and later, this file is a symbolic link containing the actual
pathname of the executed command. This symbolic link can be dereferenced normally;
attempting to open it will open the executable. You can even type /proc/[pid]/exe
to run another copy of the same executable that is being run by process [pid]. If
the pathname has been unlinked, the symbolic link will contain the string
'(deleted)' appended to the original pathname. In a multithreaded process, the
contents of this symbolic link are not available if the main thread has already
terminated (typically by calling pthread_exit(3)).
Under Linux 2.0 and earlier, /proc/[pid]/exe is a pointer to the binary which was
executed, and appears as a symbolic link. A readlink(2) call on this file under
Linux 2.0 returns a string in the format:
[device]:inode
For example, [0301]:1502 would be inode 1502 on device major 03 (IDE, MFM, etc.
drives) minor 01 (first partition on the first drive).
find(1) with the -inum option can be used to locate the file.
/proc/[pid]/fd/
This is a subdirectory containing one entry for each file which the process has
open, named by its file descriptor, and which is a symbolic link to the actual
file. Thus, 0 is standard input, 1 standard output, 2 standard error, and so on.
For file descriptors for pipes and sockets, the entries will be symbolic links
whose content is the file type with the inode. A readlink(2) call on this file
returns a string in the format:
type:[inode]
For example, socket:[2248868] will be a socket and its inode is 2248868. For
sockets, that inode can be used to find more information in one of the files under
/proc/net/.
For file descriptors that have no corresponding inode (e.g., file descriptors
produced by epoll_create(2), eventfd(2), inotify_init(2), signalfd(2), and
timerfd(2)), the entry will be a symbolic link with contents of the form
anon_inode:<file-type>
In some cases, the file-type is surrounded by square brackets.
For example, an epoll file descriptor will have a symbolic link whose content is
the string anon_inode:[eventpoll].
In a multithreaded process, the contents of this directory are not available if the
main thread has already terminated (typically by calling pthread_exit(3)).
Programs that will take a filename as a command-line argument, but will not take
input from standard input if no argument is supplied, or that write to a file named
as a command-line argument, but will not send their output to standard output if no
argument is supplied, can nevertheless be made to use standard input or standard
out using /proc/[pid]/fd. For example, assuming that -i is the flag designating an
input file and -o is the flag designating an output file:
$ foobar -i /proc/self/fd/0 -o /proc/self/fd/1 ...
and you have a working filter.
/proc/self/fd/N is approximately the same as /dev/fd/N in some UNIX and UNIX-like
systems. Most Linux MAKEDEV scripts symbolically link /dev/fd to /proc/self/fd, in
fact.
Most systems provide symbolic links /dev/stdin, /dev/stdout, and /dev/stderr, which
respectively link to the files 0, 1, and 2 in /proc/self/fd. Thus the example
command above could be written as:
$ foobar -i /dev/stdin -o /dev/stdout ...
/proc/[pid]/fdinfo/ (since Linux 2.6.22)
This is a subdirectory containing one entry for each file which the process has
open, named by its file descriptor. The files in this directory are readable only
by the owner of the process. The contents of each file can be read to obtain
information about the corresponding file descriptor. The content depends on the
type of file referred to by the corresponding descriptor.
For regular files and directories, we see something like:
$ cat /proc/12015/fdinfo/4
pos: 1000
flags: 01002002
mnt_id: 21
The pos field is a decimal number showing the current file offset. The flags field
is an octal number that displays the file access mode and file status flags (see
open(2)). The mnt_id field, present since Linux 3.15, is the ID of the mount point
containing this file. See the description of /proc/[pid]/mountinfo.
For eventfd file descriptors (see eventfd(2)), we see the following fields:
pos: 0
flags: 02
mnt_id: 10
eventfd-count: 40
eventfd-count is the current value of the eventfd counter, in hexadecimal.
For epoll file descriptors (see epoll(7)), we see the following fields:
pos: 0
flags: 02
mnt_id: 10
tfd: 9 events: 19 data: 74253d2500000009
tfd: 7 events: 19 data: 74253d2500000007
Each of the lines beginning tfd describes one of the file descriptors being
monitored via the epoll file descriptor (see epoll_ctl(2) for some details). The
tfd field is the number of the file descriptor. The events field is a hexadecimal
mask of the events being monitored for this file descriptor. The data field is the
data value associated with this file descriptor.
For signalfd file descriptors (see signalfd(2)), we see the following fields:
pos: 0
flags: 02
mnt_id: 10
sigmask: 0000000000000006
sigmask is the hexadecimal mask of signals that are accepted via this signalfd file
descriptor. (In this example, bits 2 and 3 are set, corresponding to the signals
SIGINT and SIGQUIT; see signal(7).)
/proc/[pid]/io (since kernel 2.6.20)
This file contains I/O statistics for the process, for example:
# cat /proc/3828/io
rchar: 323934931
wchar: 323929600
syscr: 632687
syscw: 632675
read_bytes: 0
write_bytes: 323932160
cancelled_write_bytes: 0
The fields are as follows:
rchar: characters read
The number of bytes which this task has caused to be read from storage.
This is simply the sum of bytes which this process passed to read(2) and
similar system calls. It includes things such as terminal I/O and is
unaffected by whether or not actual physical disk I/O was required (the read
might have been satisfied from pagecache).
wchar: characters written
The number of bytes which this task has caused, or shall cause to be written
to disk. Similar caveats apply here as with rchar.
syscr: read syscalls
Attempt to count the number of read I/O operations—that is, system calls
such as read(2) and pread(2).
syscw: write syscalls
Attempt to count the number of write I/O operations—that is, system calls
such as write(2) and pwrite(2).
read_bytes: bytes read
Attempt to count the number of bytes which this process really did cause to
be fetched from the storage layer. This is accurate for block-backed
filesystems.
write_bytes: bytes written
Attempt to count the number of bytes which this process caused to be sent to
the storage layer.
cancelled_write_bytes:
The big inaccuracy here is truncate. If a process writes 1MB to a file and
then deletes the file, it will in fact perform no writeout. But it will
have been accounted as having caused 1MB of write. In other words: this
field represents the number of bytes which this process caused to not
happen, by truncating pagecache. A task can cause "negative" I/O too. If
this task truncates some dirty pagecache, some I/O which another task has
been accounted for (in its write_bytes) will not be happening.
Note: In the current implementation, things are a bit racy on 32-bit systems: if
process A reads process B's /proc/[pid]/io while process B is updating one of these
64-bit counters, process A could see an intermediate result.
/proc/[pid]/gid_map (since Linux 3.5)
See user_namespaces(7).
/proc/[pid]/limits (since Linux 2.6.24)
This file displays the soft limit, hard limit, and units of measurement for each of
the process's resource limits (see getrlimit(2)). Up to and including Linux
2.6.35, this file is protected to allow reading only by the real UID of the
process. Since Linux 2.6.36, this file is readable by all users on the system.
/proc/[pid]/map_files/ (since kernel 3.3)
This subdirectory contains entries corresponding to memory-mapped files (see
mmap(2)). Entries are named by memory region start and end address pair (expressed
as hexadecimal numbers), and are symbolic links to the mapped files themselves.
Here is an example, with the output wrapped and reformatted to fit on an 80-column
display:
# ls -l /proc/self/map_files/
lr--------. 1 root root 64 Apr 16 21:31
3252e00000-3252e20000 -> /usr/lib64/ld-2.15.so
...
Although these entries are present for memory regions that were mapped with the
MAP_FILE flag, the way anonymous shared memory (regions created with the MAP_ANON |
MAP_SHARED flags) is implemented in Linux means that such regions also appear on
this directory. Here is an example where the target file is the deleted /dev/zero
one:
lrw-------. 1 root root 64 Apr 16 21:33
7fc075d2f000-7fc075e6f000 -> /dev/zero (deleted)
This directory appears only if the CONFIG_CHECKPOINT_RESTORE kernel configuration
option is enabled. Privilege (CAP_SYS_ADMIN) is required to view the contents of
this directory.
/proc/[pid]/maps
A file containing the currently mapped memory regions and their access permissions.
See mmap(2) for some further information about memory mappings.
The format of the file is:
address perms offset dev inode pathname
00400000-00452000 r-xp 00000000 08:02 173521 /usr/bin/dbus-daemon
00651000-00652000 r--p 00051000 08:02 173521 /usr/bin/dbus-daemon
00652000-00655000 rw-p 00052000 08:02 173521 /usr/bin/dbus-daemon
00e03000-00e24000 rw-p 00000000 00:00 0 [heap]
00e24000-011f7000 rw-p 00000000 00:00 0 [heap]
...
35b1800000-35b1820000 r-xp 00000000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a1f000-35b1a20000 r--p 0001f000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a20000-35b1a21000 rw-p 00020000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a21000-35b1a22000 rw-p 00000000 00:00 0
35b1c00000-35b1dac000 r-xp 00000000 08:02 135870 /usr/lib64/libc-2.15.so
35b1dac000-35b1fac000 ---p 001ac000 08:02 135870 /usr/lib64/libc-2.15.so
35b1fac000-35b1fb0000 r--p 001ac000 08:02 135870 /usr/lib64/libc-2.15.so
35b1fb0000-35b1fb2000 rw-p 001b0000 08:02 135870 /usr/lib64/libc-2.15.so
...
f2c6ff8c000-7f2c7078c000 rw-p 00000000 00:00 0 [stack:986]
...
7fffb2c0d000-7fffb2c2e000 rw-p 00000000 00:00 0 [stack]
7fffb2d48000-7fffb2d49000 r-xp 00000000 00:00 0 [vdso]
The address field is the address space in the process that the mapping occupies.
The perms field is a set of permissions:
r = read
w = write
x = execute
s = shared
p = private (copy on write)
The offset field is the offset into the file/whatever; dev is the device
(major:minor); inode is the inode on that device. 0 indicates that no inode is
associated with the memory region, as would be the case with BSS (uninitialized
data).
The pathname field will usually be the file that is backing the mapping. For ELF
files, you can easily coordinate with the offset field by looking at the Offset
field in the ELF program headers (readelf -l).
There are additional helpful pseudo-paths:
[stack]
The initial process's (also known as the main thread's) stack.
[stack:<tid>] (since Linux 3.4)
A thread's stack (where the <tid> is a thread ID). It corresponds to
the /proc/[pid]/task/[tid]/ path.
[vdso] The virtual dynamically linked shared object.
[heap] The process's heap.
If the pathname field is blank, this is an anonymous mapping as obtained via the
mmap(2) function. There is no easy way to coordinate this back to a process's
source, short of running it through gdb(1), strace(1), or similar.
Under Linux 2.0, there is no field giving pathname.
/proc/[pid]/mem
This file can be used to access the pages of a process's memory through open(2),
read(2), and lseek(2).
/proc/[pid]/mountinfo (since Linux 2.6.26)
This file contains information about mount points. It contains lines of the form:
36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
The numbers in parentheses are labels for the descriptions below:
(1) mount ID: unique identifier of the mount (may be reused after umount(2)).
(2) parent ID: ID of parent mount (or of self for the top of the mount tree).
(3) major:minor: value of st_dev for files on filesystem (see stat(2)).
(4) root: root of the mount within the filesystem.
(5) mount point: mount point relative to the process's root.
(6) mount options: per-mount options.
(7) optional fields: zero or more fields of the form "tag[:value]".
(8) separator: marks the end of the optional fields.
(9) filesystem type: name of filesystem in the form "type[.subtype]".
(10) mount source: filesystem-specific information or "none".
(11) super options: per-superblock options.
Parsers should ignore all unrecognized optional fields. Currently the possible
optional fields are:
shared:X mount is shared in peer group X
master:X mount is slave to peer group X
propagate_from:X mount is slave and receives propagation from peer group X
(*)
unbindable mount is unbindable
(*) X is the closest dominant peer group under the process's root. If X is the
immediate master of the mount, or if there is no dominant peer group under the same
root, then only the "master:X" field is present and not the "propagate_from:X"
field.
For more information on mount propagation see:
Documentation/filesystems/sharedsubtree.txt in the Linux kernel source tree.
/proc/[pid]/mounts (since Linux 2.4.19)
This is a list of all the filesystems currently mounted in the process's mount
namespace. The format of this file is documented in fstab(5). Since kernel
version 2.6.15, this file is pollable: after opening the file for reading, a change
in this file (i.e., a filesystem mount or unmount) causes select(2) to mark the
file descriptor as readable, and poll(2) and epoll_wait(2) mark the file as having
an error condition. See namespaces(7) for more information.
/proc/[pid]/mountstats (since Linux 2.6.17)
This file exports information (statistics, configuration information) about the
mount points in the process's mount namespace. Lines in this file have the form:
device /dev/sda7 mounted on /home with fstype ext3 [statistics]
( 1 ) ( 2 ) (3 ) (4)
The fields in each line are:
(1) The name of the mounted device (or "nodevice" if there is no corresponding
device).
(2) The mount point within the filesystem tree.
(3) The filesystem type.
(4) Optional statistics and configuration information. Currently (as at Linux
2.6.26), only NFS filesystems export information via this field.
This file is readable only by the owner of the process.
See namespaces(7) for more information.
/proc/[pid]/ns/ (since Linux 3.0)
This is a subdirectory containing one entry for each namespace that supports being
manipulated by setns(2). For more information, see namespaces(7).
/proc/[pid]/numa_maps (since Linux 2.6.14)
See numa(7).
/proc/[pid]/oom_adj (since Linux 2.6.11)
This file can be used to adjust the score used to select which process should be
killed in an out-of-memory (OOM) situation. The kernel uses this value for a bit-
shift operation of the process's oom_score value: valid values are in the range -16
to +15, plus the special value -17, which disables OOM-killing altogether for this
process. A positive score increases the likelihood of this process being killed by
the OOM-killer; a negative score decreases the likelihood.
The default value for this file is 0; a new process inherits its parent's oom_adj
setting. A process must be privileged (CAP_SYS_RESOURCE) to update this file.
Since Linux 2.6.36, use of this file is deprecated in favor of
/proc/[pid]/oom_score_adj.
/proc/[pid]/oom_score (since Linux 2.6.11)
This file displays the current score that the kernel gives to this process for the
purpose of selecting a process for the OOM-killer. A higher score means that the
process is more likely to be selected by the OOM-killer. The basis for this score
is the amount of memory used by the process, with increases (+) or decreases (-)
for factors including:
* whether the process creates a lot of children using fork(2) (+);
* whether the process has been running a long time, or has used a lot of CPU time
(-);
* whether the process has a low nice value (i.e., > 0) (+);
* whether the process is privileged (-); and
* whether the process is making direct hardware access (-).
The oom_score also reflects the adjustment specified by the oom_score_adj or
oom_adj setting for the process.
/proc/[pid]/oom_score_adj (since Linux 2.6.36)
This file can be used to adjust the badness heuristic used to select which process
gets killed in out-of-memory conditions.
The badness heuristic assigns a value to each candidate task ranging from 0 (never
kill) to 1000 (always kill) to determine which process is targeted. The units are
roughly a proportion along that range of allowed memory the process may allocate
from, based on an estimation of its current memory and swap use. For example, if a
task is using all allowed memory, its badness score will be 1000. If it is using
half of its allowed memory, its score will be 500.
There is an additional factor included in the badness score: root processes are
given 3% extra memory over other tasks.
The amount of "allowed" memory depends on the context in which the OOM-killer was
called. If it is due to the memory assigned to the allocating task's cpuset being
exhausted, the allowed memory represents the set of mems assigned to that cpuset
(see cpuset(7)). If it is due to a mempolicy's node(s) being exhausted, the
allowed memory represents the set of mempolicy nodes. If it is due to a memory
limit (or swap limit) being reached, the allowed memory is that configured limit.
Finally, if it is due to the entire system being out of memory, the allowed memory
represents all allocatable resources.
The value of oom_score_adj is added to the badness score before it is used to
determine which task to kill. Acceptable values range from -1000
(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows user space to
control the preference for OOM-killing, ranging from always preferring a certain
task or completely disabling it from OOM killing. The lowest possible value,
-1000, is equivalent to disabling OOM-killing entirely for that task, since it will
always report a badness score of 0.
Consequently, it is very simple for user space to define the amount of memory to
consider for each task. Setting a oom_score_adj value of +500, for example, is
roughly equivalent to allowing the remainder of tasks sharing the same system,
cpuset, mempolicy, or memory controller resources to use at least 50% more memory.
A value of -500, on the other hand, would be roughly equivalent to discounting 50%
of the task's allowed memory from being considered as scoring against the task.
For backward compatibility with previous kernels, /proc/[pid]/oom_adj can still be
used to tune the badness score. Its value is scaled linearly with oom_score_adj.
Writing to /proc/[pid]/oom_score_adj or /proc/[pid]/oom_adj will change the other
with its scaled value.
/proc/[pid]/pagemap (since Linux 2.6.25)
This file shows the mapping of each of the process's virtual pages into physical
page frames or swap area. It contains one 64-bit value for each virtual page, with
the bits set as follows:
63 If set, the page is present in RAM.
62 If set, the page is in swap space
61 (since Linux 3.5)
The page is a file-mapped page or a shared anonymous page.
60-56 (since Linux 3.11)
Zero
55 (Since Linux 3.11)
PTE is soft-dirty (see the kernel source file Documentation/vm/soft-
dirty.txt).
54-0 If the page is present in RAM (bit 63), then these bits provide the
page frame number, which can be used to index /proc/kpageflags and
/proc/kpagecount. If the page is present in swap (bit 62), then bits
4-0 give the swap type, and bits 54-5 encode the swap offset.
Before Linux 3.11, bits 60-55 were used to encode the base-2 log of the page size.
To employ /proc/[pid]/pagemap efficiently, use /proc/[pid]/maps to determine which
areas of memory are actually mapped and seek to skip over unmapped regions.
The /proc/[pid]/pagemap file is present only if the CONFIG_PROC_PAGE_MONITOR kernel
configuration option is enabled.
/proc/[pid]/personality (since Linux 2.6.28)
This read-only file exposes the process's execution domain, as set by
personality(2). The value is displayed in hexadecimal notation.
/proc/[pid]/root
UNIX and Linux support the idea of a per-process root of the filesystem, set by the
chroot(2) system call. This file is a symbolic link that points to the process's
root directory, and behaves in the same way as exe, and fd/*.
In a multithreaded process, the contents of this symbolic link are not available if
the main thread has already terminated (typically by calling pthread_exit(3)).
/proc/[pid]/seccomp (from Linux 2.6.12 to 2.6.22)
Read/set the seccomp mode for the process. If this file contains the value zero,
seccomp mode is not enabled. Writing the value 1 to this file (irreversibly)
places the process in seccomp mode: the only permitted system calls are read(2),
write(2), _exit(2), and sigreturn(2). This file went away in Linux 2.6.23, when it
was replaced by a prctl(2)-based mechanism.
/proc/[pid]/setgroups (since Linux 3.19)
See user_namespaces(7).
/proc/[pid]/smaps (since Linux 2.6.14)
This file shows memory consumption for each of the process's mappings. (The
pmap(1) command displays similar information, in a form that may be easier for
parsing.) For each mapping there is a series of lines such as the following:
00400000-0048a000 r-xp 00000000 fd:03 960637 /bin/bash
Size: 552 kB
Rss: 460 kB
Pss: 100 kB
Shared_Clean: 452 kB
Shared_Dirty: 0 kB
Private_Clean: 8 kB
Private_Dirty: 0 kB
Referenced: 460 kB
Anonymous: 0 kB
AnonHugePages: 0 kB
Swap: 0 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
Locked: 0 kB
The first of these lines shows the same information as is displayed for the mapping
in /proc/[pid]/maps. The remaining lines show the size of the mapping, the amount
of the mapping that is currently resident in RAM ("Rss"), the process' proportional
share of this mapping ("Pss"), the number of clean and dirty shared pages in the
mapping, and the number of clean and dirty private pages in the mapping.
"Referenced" indicates the amount of memory currently marked as referenced or
accessed. "Anonymous" shows the amount of memory that does not belong to any file.
"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
The "KernelPageSize" entry is the page size used by the kernel to back a VMA. This
matches the size used by the MMU in the majority of cases. However, one counter-
example occurs on PPC64 kernels whereby a kernel using 64K as a base page size may
still use 4K pages for the MMU on older processors. To distinguish, this patch
reports "MMUPageSize" as the page size used by the MMU.
The "Locked" indicates whether the mapping is locked in memory or not.
"VmFlags" field represents the kernel flags associated with the particular virtual
memory area in two letter encoded manner. The codes are the following:
rd - readable
wr - writable
ex - executable
sh - shared
mr - may read
mw - may write
me - may execute
ms - may share
gd - stack segment grows down
pf - pure PFN range
dw - disabled write to the mapped file
lo - pages are locked in memory
io - memory mapped I/O area
sr - sequential read advise provided
rr - random read advise provided
dc - do not copy area on fork
de - do not expand area on remapping
ac - area is accountable
nr - swap space is not reserved for the area
ht - area uses huge tlb pages
nl - non-linear mapping
ar - architecture specific flag
dd - do not include area into core dump
sd - soft-dirty flag
mm - mixed map area
hg - huge page advise flag
nh - no-huge page advise flag
mg - mergeable advise flag
The /proc/[pid]/smaps file is present only if the CONFIG_PROC_PAGE_MONITOR kernel
configuration option is enabled.
/proc/[pid]/stack (since Linux 2.6.29)
This file provides a symbolic trace of the function calls in this process's kernel
stack. This file is provided only if the kernel was built with the
CONFIG_STACKTRACE configuration option.
/proc/[pid]/stat
Status information about the process. This is used by ps(1). It is defined in the
kernel source file fs/proc/array.c.
The fields, in order, with their proper scanf(3) format specifiers, are:
(1) pid %d
The process ID.
(2) comm %s
The filename of the executable, in parentheses. This is visible whether
or not the executable is swapped out.
(3) state %c
One of the following characters, indicating process state:
R Running
S Sleeping in an interruptible wait
D Waiting in uninterruptible disk sleep
Z Zombie
T Stopped (on a signal) or (before Linux 2.6.33) trace stopped
t Tracing stop (Linux 2.6.33 onward)
W Paging (only before Linux 2.6.0)
X Dead (from Linux 2.6.0 onward)
x Dead (Linux 2.6.33 to 3.13 only)
K Wakekill (Linux 2.6.33 to 3.13 only)
W Waking (Linux 2.6.33 to 3.13 only)
P Parked (Linux 3.9 to 3.13 only)
(4) ppid %d
The PID of the parent of this process.
(5) pgrp %d
The process group ID of the process.
(6) session %d
The session ID of the process.
(7) tty_nr %d
The controlling terminal of the process. (The minor device number is
contained in the combination of bits 31 to 20 and 7 to 0; the major
device number is in bits 15 to 8.)
(8) tpgid %d
The ID of the foreground process group of the controlling terminal of the
process.
(9) flags %u
The kernel flags word of the process. For bit meanings, see the PF_*
defines in the Linux kernel source file include/linux/sched.h. Details
depend on the kernel version.
The format for this field was %lu before Linux 2.6.
(10) minflt %lu
The number of minor faults the process has made which have not required
loading a memory page from disk.
(11) cminflt %lu
The number of minor faults that the process's waited-for children have
made.
(12) majflt %lu
The number of major faults the process has made which have required
loading a memory page from disk.
(13) cmajflt %lu
The number of major faults that the process's waited-for children have
made.
(14) utime %lu
Amount of time that this process has been scheduled in user mode,
measured in clock ticks (divide by sysconf(_SC_CLK_TCK)). This includes
guest time, guest_time (time spent running a virtual CPU, see below), so
that applications that are not aware of the guest time field do not lose
that time from their calculations.
(15) stime %lu
Amount of time that this process has been scheduled in kernel mode,
measured in clock ticks (divide by sysconf(_SC_CLK_TCK)).
(16) cutime %ld
Amount of time that this process's waited-for children have been
scheduled in user mode, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)). (See also times(2).) This includes guest time,
cguest_time (time spent running a virtual CPU, see below).
(17) cstime %ld
Amount of time that this process's waited-for children have been
scheduled in kernel mode, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)).
(18) priority %ld
(Explanation for Linux 2.6) For processes running a real-time scheduling
policy (policy below; see sched_setscheduler(2)), this is the negated
scheduling priority, minus one; that is, a number in the range -2 to
-100, corresponding to real-time priorities 1 to 99. For processes
running under a non-real-time scheduling policy, this is the raw nice
value (setpriority(2)) as represented in the kernel. The kernel stores
nice values as numbers in the range 0 (high) to 39 (low), corresponding
to the user-visible nice range of -20 to 19.
Before Linux 2.6, this was a scaled value based on the scheduler
weighting given to this process.
(19) nice %ld
The nice value (see setpriority(2)), a value in the range 19 (low
priority) to -20 (high priority).
(20) num_threads %ld
Number of threads in this process (since Linux 2.6). Before kernel 2.6,
this field was hard coded to 0 as a placeholder for an earlier removed
field.
(21) itrealvalue %ld
The time in jiffies before the next SIGALRM is sent to the process due to
an interval timer. Since kernel 2.6.17, this field is no longer
maintained, and is hard coded as 0.
(22) starttime %llu
The time the process started after system boot. In kernels before Linux
2.6, this value was expressed in jiffies. Since Linux 2.6, the value is
expressed in clock ticks (divide by sysconf(_SC_CLK_TCK)).
The format for this field was %lu before Linux 2.6.
(23) vsize %lu
Virtual memory size in bytes.
(24) rss %ld
Resident Set Size: number of pages the process has in real memory. This
is just the pages which count toward text, data, or stack space. This
does not include pages which have not been demand-loaded in, or which are
swapped out.
(25) rsslim %lu
Current soft limit in bytes on the rss of the process; see the
description of RLIMIT_RSS in getrlimit(2).
(26) startcode %lu
The address above which program text can run.
(27) endcode %lu
The address below which program text can run.
(28) startstack %lu
The address of the start (i.e., bottom) of the stack.
(29) kstkesp %lu
The current value of ESP (stack pointer), as found in the kernel stack
page for the process.
(30) kstkeip %lu
The current EIP (instruction pointer).
(31) signal %lu
The bitmap of pending signals, displayed as a decimal number. Obsolete,
because it does not provide information on real-time signals; use
/proc/[pid]/status instead.
(32) blocked %lu
The bitmap of blocked signals, displayed as a decimal number. Obsolete,
because it does not provide information on real-time signals; use
/proc/[pid]/status instead.
(33) sigignore %lu
The bitmap of ignored signals, displayed as a decimal number. Obsolete,
because it does not provide information on real-time signals; use
/proc/[pid]/status instead.
(34) sigcatch %lu
The bitmap of caught signals, displayed as a decimal number. Obsolete,
because it does not provide information on real-time signals; use
/proc/[pid]/status instead.
(35) wchan %lu
This is the "channel" in which the process is waiting. It is the address
of a location in the kernel where the process is sleeping. The
corresponding symbolic name can be found in /proc/[pid]/wchan.
(36) nswap %lu
Number of pages swapped (not maintained).
(37) cnswap %lu
Cumulative nswap for child processes (not maintained).
(38) exit_signal %d (since Linux 2.1.22)
Signal to be sent to parent when we die.
(39) processor %d (since Linux 2.2.8)
CPU number last executed on.
(40) rt_priority %u (since Linux 2.5.19)
Real-time scheduling priority, a number in the range 1 to 99 for
processes scheduled under a real-time policy, or 0, for non-real-time
processes (see sched_setscheduler(2)).
(41) policy %u (since Linux 2.5.19)
Scheduling policy (see sched_setscheduler(2)). Decode using the SCHED_*
constants in linux/sched.h.
The format for this field was %lu before Linux 2.6.22.
(42) delayacct_blkio_ticks %llu (since Linux 2.6.18)
Aggregated block I/O delays, measured in clock ticks (centiseconds).
(43) guest_time %lu (since Linux 2.6.24)
Guest time of the process (time spent running a virtual CPU for a guest
operating system), measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)).
(44) cguest_time %ld (since Linux 2.6.24)
Guest time of the process's children, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)).
(45) start_data %lu (since Linux 3.3)
Address above which program initialized and uninitialized (BSS) data are
placed.
(46) end_data %lu (since Linux 3.3)
Address below which program initialized and uninitialized (BSS) data are
placed.
(47) start_brk %lu (since Linux 3.3)
Address above which program heap can be expanded with brk(2).
(48) arg_start %lu (since Linux 3.5)
Address above which program command-line arguments (argv) are placed.
(49) arg_end %lu (since Linux 3.5)
Address below program command-line arguments (argv) are placed.
(50) env_start %lu (since Linux 3.5)
Address above which program environment is placed.
(51) env_end %lu (since Linux 3.5)
Address below which program environment is placed.
(52) exit_code %d (since Linux 3.5)
The thread's exit status in the form reported by waitpid(2).
/proc/[pid]/statm
Provides information about memory usage, measured in pages. The columns are:
size (1) total program size
(same as VmSize in /proc/[pid]/status)
resident (2) resident set size
(same as VmRSS in /proc/[pid]/status)
share (3) shared pages (i.e., backed by a file)
text (4) text (code)
lib (5) library (unused in Linux 2.6)
data (6) data + stack
dt (7) dirty pages (unused in Linux 2.6)
/proc/[pid]/status
Provides much of the information in /proc/[pid]/stat and /proc/[pid]/statm in a
format that's easier for humans to parse. Here's an example:
$ cat /proc/$$/status
Name: bash
State: S (sleeping)
Tgid: 3515
Pid: 3515
PPid: 3452
TracerPid: 0
Uid: 1000 1000 1000 1000
Gid: 100 100 100 100
FDSize: 256
Groups: 16 33 100
VmPeak: 9136 kB
VmSize: 7896 kB
VmLck: 0 kB
VmPin: 0 kB
VmHWM: 7572 kB
VmRSS: 6316 kB
VmData: 5224 kB
VmStk: 88 kB
VmExe: 572 kB
VmLib: 1708 kB
VmPMD: 4 kB
VmPTE: 20 kB
VmSwap: 0 kB
Threads: 1
SigQ: 0/3067
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000010000
SigIgn: 0000000000384004
SigCgt: 000000004b813efb
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
CapAmb: 0000000000000000
Seccomp: 0
Cpus_allowed: 00000001
Cpus_allowed_list: 0
Mems_allowed: 1
Mems_allowed_list: 0
voluntary_ctxt_switches: 150
nonvoluntary_ctxt_switches: 545
The fields are as follows:
* Name: Command run by this process.
* State: Current state of the process. One of "R (running)", "S (sleeping)", "D
(disk sleep)", "T (stopped)", "T (tracing stop)", "Z (zombie)", or "X (dead)".
* Tgid: Thread group ID (i.e., Process ID).
* Pid: Thread ID (see gettid(2)).
* PPid: PID of parent process.
* TracerPid: PID of process tracing this process (0 if not being traced).
* Uid, Gid: Real, effective, saved set, and filesystem UIDs (GIDs).
* FDSize: Number of file descriptor slots currently allocated.
* Groups: Supplementary group list.
* VmPeak: Peak virtual memory size.
* VmSize: Virtual memory size.
* VmLck: Locked memory size (see mlock(3)).
* VmPin: Pinned memory size (since Linux 3.2). These are pages that can't be moved
because something needs to directly access physical memory.
* VmHWM: Peak resident set size ("high water mark").
* VmRSS: Resident set size.
* VmData, VmStk, VmExe: Size of data, stack, and text segments.
* VmLib: Shared library code size.
* VmPTE: Page table entries size (since Linux 2.6.10).
* VmPMD: Size of second-level page tables (since Linux 4.0).
* VmSwap: Swapped-out virtual memory size by anonymous private pages; shmem swap
usage is not included (since Linux 2.6.34).
* Threads: Number of threads in process containing this thread.
* SigQ: This field contains two slash-separated numbers that relate to queued
signals for the real user ID of this process. The first of these is the number
of currently queued signals for this real user ID, and the second is the resource
limit on the number of queued signals for this process (see the description of
RLIMIT_SIGPENDING in getrlimit(2)).
* SigPnd, ShdPnd: Number of signals pending for thread and for process as a whole
(see pthreads(7) and signal(7)).
* SigBlk, SigIgn, SigCgt: Masks indicating signals being blocked, ignored, and
caught (see signal(7)).
* CapInh, CapPrm, CapEff: Masks of capabilities enabled in inheritable, permitted,
and effective sets (see capabilities(7)).
* CapBnd: Capability Bounding set (since Linux 2.6.26, see capabilities(7)).
* CapAmb: Ambient capability set (since Linux 4.3, see capabilities(7)).
* Seccomp: Seccomp mode of the process (since Linux 3.8, see seccomp(2)). 0 means
SECCOMP_MODE_DISABLED; 1 means SECCOMP_MODE_STRICT; 2 means SECCOMP_MODE_FILTER.
This field is provided only if the kernel was built with the CONFIG_SECCOMP
kernel configuration option enabled.
* Cpus_allowed: Mask of CPUs on which this process may run (since Linux 2.6.24, see
cpuset(7)).
* Cpus_allowed_list: Same as previous, but in "list format" (since Linux 2.6.26,
see cpuset(7)).
* Mems_allowed: Mask of memory nodes allowed to this process (since Linux 2.6.24,
see cpuset(7)).
* Mems_allowed_list: Same as previous, but in "list format" (since Linux 2.6.26,
see cpuset(7)).
* voluntary_ctxt_switches, nonvoluntary_ctxt_switches: Number of voluntary and
involuntary context switches (since Linux 2.6.23).
/proc/[pid]/syscall (since Linux 2.6.27)
This file exposes the system call number and argument registers for the system call
currently being executed by the process, followed by the values of the stack
pointer and program counter registers. The values of all six argument registers
are exposed, although most system calls use fewer registers.
If the process is blocked, but not in a system call, then the file displays -1 in
place of the system call number, followed by just the values of the stack pointer
and program counter. If process is not blocked, then the file contains just the
string "running".
This file is present only if the kernel was configured with
CONFIG_HAVE_ARCH_TRACEHOOK.
/proc/[pid]/task (since Linux 2.6.0-test6)
This is a directory that contains one subdirectory for each thread in the process.
The name of each subdirectory is the numerical thread ID ([tid]) of the thread (see
gettid(2)). Within each of these subdirectories, there is a set of files with the
same names and contents as under the /proc/[pid] directories. For attributes that
are shared by all threads, the contents for each of the files under the task/[tid]
subdirectories will be the same as in the corresponding file in the parent
/proc/[pid] directory (e.g., in a multithreaded process, all of the task/[tid]/cwd
files will have the same value as the /proc/[pid]/cwd file in the parent directory,
since all of the threads in a process share a working directory). For attributes
that are distinct for each thread, the corresponding files under task/[tid] may
have different values (e.g., various fields in each of the task/[tid]/status files
may be different for each thread).
In a multithreaded process, the contents of the /proc/[pid]/task directory are not
available if the main thread has already terminated (typically by calling
pthread_exit(3)).
/proc/[pid]/timers (since Linux 3.10)
A list of the POSIX timers for this process. Each timer is listed with a line that
starts with the string "ID:". For example:
ID: 1
signal: 60/00007fff86e452a8
notify: signal/pid.2634
ClockID: 0
ID: 0
signal: 60/00007fff86e452a8
notify: signal/pid.2634
ClockID: 1
The lines shown for each timer have the following meanings:
ID The ID for this timer. This is not the same as the timer ID returned by
timer_create(2); rather, it is the same kernel-internal ID that is available
via the si_timerid field of the siginfo_t structure (see sigaction(2)).
signal This is the signal number that this timer uses to deliver notifications
followed by a slash, and then the sigev_value value supplied to the signal
handler. Valid only for timers that notify via a signal.
notify The part before the slash specifies the mechanism that this timer uses to
deliver notifications, and is one of "thread", "signal", or "none".
Immediately following the slash is either the string "tid" for timers with
SIGEV_THREAD_ID notification, or "pid" for timers that notify by other
mechanisms. Following the "." is the PID of the process (or the kernel
thread ID of the thread) that will be delivered a signal if the timer
delivers notifications via a signal.
ClockID
This field identifies the clock that the timer uses for measuring time. For
most clocks, this is a number that matches one of the user-space CLOCK_*
constants exposed via <time.h>. CLOCK_PROCESS_CPUTIME_ID timers display
with a value of -6 in this field. CLOCK_THREAD_CPUTIME_ID timers display
with a value of -2 in this field.
This file is available only when the kernel was configured with
CONFIG_CHECKPOINT_RESTORE.
/proc/[pid]/uid_map, /proc/[pid]/gid_map (since Linux 3.5)
See user_namespaces(7).
/proc/[pid]/wchan (since Linux 2.6.0)
The symbolic name corresponding to the location in the kernel where the process is
sleeping.
/proc/apm
Advanced power management version and battery information when CONFIG_APM is
defined at kernel compilation time.
/proc/buddyinfo
This file contains information which is used for diagnosing memory fragmentation
issues. Each line starts with the identification of the node and the name of the
zone which together identify a memory region This is then followed by the count of
available chunks of a certain order in which these zones are split. The size in
bytes of a certain order is given by the formula:
(2^order) * PAGE_SIZE
The binary buddy allocator algorithm inside the kernel will split one chunk into
two chunks of a smaller order (thus with half the size) or combine two contiguous
chunks into one larger chunk of a higher order (thus with double the size) to
satisfy allocation requests and to counter memory fragmentation. The order matches
the column number, when starting to count at zero.
For example on a x86_64 system:
Node 0, zone DMA 1 1 1 0 2 1 1 0 1 1 3
Node 0, zone DMA32 65 47 4 81 52 28 13 10 5 1 404
Node 0, zone Normal 216 55 189 101 84 38 37 27 5 3 587
In this example, there is one node containing three zones and there are 11
different chunk sizes. If the page size is 4 kilobytes, then the first zone called
DMA (on x86 the first 16 megabyte of memory) has 1 chunk of 4 kilobytes (order 0)
available and has 3 chunks of 4 megabytes (order 10) available.
If the memory is heavily fragmented, the counters for higher order chunks will be
zero and allocation of large contiguous areas will fail.
Further information about the zones can be found in /proc/zoneinfo.
/proc/bus
Contains subdirectories for installed busses.
/proc/bus/pccard
Subdirectory for PCMCIA devices when CONFIG_PCMCIA is set at kernel compilation
time.
/proc/bus/pccard/drivers
/proc/bus/pci
Contains various bus subdirectories and pseudo-files containing information about
PCI busses, installed devices, and device drivers. Some of these files are not
ASCII.
/proc/bus/pci/devices
Information about PCI devices. They may be accessed through lspci(8) and
setpci(8).
/proc/cmdline
Arguments passed to the Linux kernel at boot time. Often done via a boot manager
such as lilo(8) or grub(8).
/proc/config.gz (since Linux 2.6)
This file exposes the configuration options that were used to build the currently
running kernel, in the same format as they would be shown in the .config file that
resulted when configuring the kernel (using make xconfig, make config, or similar).
The file contents are compressed; view or search them using zcat(1) and zgrep(1).
As long as no changes have been made to the following file, the contents of
/proc/config.gz are the same as those provided by :
cat /lib/modules/$(uname -r)/build/.config
/proc/config.gz is provided only if the kernel is configured with
CONFIG_IKCONFIG_PROC.
/proc/crypto
A list of the ciphers provided by the kernel crypto API. For details, see the
kernel Linux Kernel Crypto API documentation available under the kernel source
directory Documentation/DocBook. (That documentation can be built using a command
such as make htmldocs in the root directory of the kernel source tree.)
/proc/cpuinfo
This is a collection of CPU and system architecture dependent items, for each
supported architecture a different list. Two common entries are processor which
gives CPU number and bogomips; a system constant that is calculated during kernel
initialization. SMP machines have information for each CPU. The lscpu(1) command
gathers its information from this file.
/proc/devices
Text listing of major numbers and device groups. This can be used by MAKEDEV
scripts for consistency with the kernel.
/proc/diskstats (since Linux 2.5.69)
This file contains disk I/O statistics for each disk device. See the Linux kernel
source file Documentation/iostats.txt for further information.
/proc/dma
This is a list of the registered ISA DMA (direct memory access) channels in use.
/proc/driver
Empty subdirectory.
/proc/execdomains
List of the execution domains (ABI personalities).
/proc/fb
Frame buffer information when CONFIG_FB is defined during kernel compilation.
/proc/filesystems
A text listing of the filesystems which are supported by the kernel, namely
filesystems which were compiled into the kernel or whose kernel modules are
currently loaded. (See also filesystems(5).) If a filesystem is marked with
"nodev", this means that it does not require a block device to be mounted (e.g.,
virtual filesystem, network filesystem).
Incidentally, this file may be used by mount(8) when no filesystem is specified and
it didn't manage to determine the filesystem type. Then filesystems contained in
this file are tried (excepted those that are marked with "nodev").
/proc/fs
Contains subdirectories that in turn contain files with information about (certain)
mounted filesystems.
/proc/ide
This directory exists on systems with the IDE bus. There are directories for each
IDE channel and attached device. Files include:
cache buffer size in KB
capacity number of sectors
driver driver version
geometry physical and logical geometry
identify in hexadecimal
media media type
model manufacturer's model number
settings drive settings
smart_thresholds in hexadecimal
smart_values in hexadecimal
The hdparm(8) utility provides access to this information in a friendly format.
/proc/interrupts
This is used to record the number of interrupts per CPU per IO device. Since Linux
2.6.24, for the i386 and x86_64 architectures, at least, this also includes
interrupts internal to the system (that is, not associated with a device as such),
such as NMI (nonmaskable interrupt), LOC (local timer interrupt), and for SMP
systems, TLB (TLB flush interrupt), RES (rescheduling interrupt), CAL (remote
function call interrupt), and possibly others. Very easy to read formatting, done
in ASCII.
/proc/iomem
I/O memory map in Linux 2.4.
/proc/ioports
This is a list of currently registered Input-Output port regions that are in use.
/proc/kallsyms (since Linux 2.5.71)
This holds the kernel exported symbol definitions used by the modules(X) tools to
dynamically link and bind loadable modules. In Linux 2.5.47 and earlier, a similar
file with slightly different syntax was named ksyms.
/proc/kcore
This file represents the physical memory of the system and is stored in the ELF
core file format. With this pseudo-file, and an unstripped kernel
(/usr/src/linux/vmlinux) binary, GDB can be used to examine the current state of
any kernel data structures.
The total length of the file is the size of physical memory (RAM) plus 4KB.
/proc/kmsg
This file can be used instead of the syslog(2) system call to read kernel messages.
A process must have superuser privileges to read this file, and only one process
should read this file. This file should not be read if a syslog process is running
which uses the syslog(2) system call facility to log kernel messages.
Information in this file is retrieved with the dmesg(1) program.
/proc/kpagecount (since Linux 2.6.25)
This file contains a 64-bit count of the number of times each physical page frame
is mapped, indexed by page frame number (see the discussion of
/proc/[pid]/pagemap).
The /proc/kpagecount file is present only if the CONFIG_PROC_PAGE_MONITOR kernel
configuration option is enabled.
/proc/kpageflags (since Linux 2.6.25)
This file contains 64-bit masks corresponding to each physical page frame; it is
indexed by page frame number (see the discussion of /proc/[pid]/pagemap). The bits
are as follows:
0 - KPF_LOCKED
1 - KPF_ERROR
2 - KPF_REFERENCED
3 - KPF_UPTODATE
4 - KPF_DIRTY
5 - KPF_LRU
6 - KPF_ACTIVE
7 - KPF_SLAB
8 - KPF_WRITEBACK
9 - KPF_RECLAIM
10 - KPF_BUDDY
11 - KPF_MMAP (since Linux 2.6.31)
12 - KPF_ANON (since Linux 2.6.31)
13 - KPF_SWAPCACHE (since Linux 2.6.31)
14 - KPF_SWAPBACKED (since Linux 2.6.31)
15 - KPF_COMPOUND_HEAD (since Linux 2.6.31)
16 - KPF_COMPOUND_TAIL (since Linux 2.6.31)
16 - KPF_HUGE (since Linux 2.6.31)
18 - KPF_UNEVICTABLE (since Linux 2.6.31)
19 - KPF_HWPOISON (since Linux 2.6.31)
20 - KPF_NOPAGE (since Linux 2.6.31)
21 - KPF_KSM (since Linux 2.6.32)
22 - KPF_THP (since Linux 3.4)
For further details on the meanings of these bits, see the kernel source file
Documentation/vm/pagemap.txt. Before kernel 2.6.29, KPF_WRITEBACK, KPF_RECLAIM,
KPF_BUDDY, and KPF_LOCKED did not report correctly.
The /proc/kpageflags file is present only if the CONFIG_PROC_PAGE_MONITOR kernel
configuration option is enabled.
/proc/ksyms (Linux 1.1.23-2.5.47)
See /proc/kallsyms.
/proc/loadavg
The first three fields in this file are load average figures giving the number of
jobs in the run queue (state R) or waiting for disk I/O (state D) averaged over 1,
5, and 15 minutes. They are the same as the load average numbers given by
uptime(1) and other programs. The fourth field consists of two numbers separated
by a slash (/). The first of these is the number of currently runnable kernel
scheduling entities (processes, threads). The value after the slash is the number
of kernel scheduling entities that currently exist on the system. The fifth field
is the PID of the process that was most recently created on the system.
/proc/locks
This file shows current file locks (flock(2) and fcntl(2)) and leases (fcntl(2)).
/proc/malloc (only up to and including Linux 2.2)
This file is present only if CONFIG_DEBUG_MALLOC was defined during compilation.
/proc/meminfo
This file reports statistics about memory usage on the system. It is used by
free(1) to report the amount of free and used memory (both physical and swap) on
the system as well as the shared memory and buffers used by the kernel. Each line
of the file consists of a parameter name, followed by a colon, the value of the
parameter, and an option unit of measurement (e.g., "kB"). The list below
describes the parameter names and the format specifier required to read the field
value. Except as noted below, all of the fields have been present since at least
Linux 2.6.0. Some fields are displayed only if the kernel was configured with
various options; those dependencies are noted in the list.
MemTotal %lu
Total usable RAM (i.e., physical RAM minus a few reserved bits and the
kernel binary code).
MemFree %lu
The sum of LowFree+HighFree.
Buffers %lu
Relatively temporary storage for raw disk blocks that shouldn't get
tremendously large (20MB or so).
Cached %lu
In-memory cache for files read from the disk (the page cache). Doesn't
include SwapCached.
SwapCached %lu
Memory that once was swapped out, is swapped back in but still also is in
the swap file. (If memory pressure is high, these pages don't need to be
swapped out again because they are already in the swap file. This saves
I/O.)
Active %lu
Memory that has been used more recently and usually not reclaimed unless
absolutely necessary.
Inactive %lu
Memory which has been less recently used. It is more eligible to be
reclaimed for other purposes.
Active(anon) %lu (since Linux 2.6.28)
[To be documented.]
Inactive(anon) %lu (since Linux 2.6.28)
[To be documented.]
Active(file) %lu (since Linux 2.6.28)
[To be documented.]
Inactive(file) %lu (since Linux 2.6.28)
[To be documented.]
Unevictable %lu (since Linux 2.6.28)
(From Linux 2.6.28 to 2.6.30, CONFIG_UNEVICTABLE_LRU was required.) [To be
documented.]
Mlocked %lu (since Linux 2.6.28)
(From Linux 2.6.28 to 2.6.30, CONFIG_UNEVICTABLE_LRU was required.) [To be
documented.]
HighTotal %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.) Total amount of
highmem. Highmem is all memory above ~860MB of physical memory. Highmem
areas are for use by user-space programs, or for the page cache. The kernel
must use tricks to access this memory, making it slower to access than
lowmem.
HighFree %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.) Amount of free
highmem.
LowTotal %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.) Total amount of
lowmem. Lowmem is memory which can be used for everything that highmem can
be used for, but it is also available for the kernel's use for its own data
structures. Among many other things, it is where everything from Slab is
allocated. Bad things happen when you're out of lowmem.
LowFree %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.) Amount of free
lowmem.
MmapCopy %lu (since Linux 2.6.29)
(CONFIG_MMU is required.) [To be documented.]
SwapTotal %lu
Total amount of swap space available.
SwapFree %lu
Amount of swap space that is currently unused.
Dirty %lu
Memory which is waiting to get written back to the disk.
Writeback %lu
Memory which is actively being written back to the disk.
AnonPages %lu (since Linux 2.6.18)
Non-file backed pages mapped into user-space page tables.
Mapped %lu
Files which have been mapped into memory (with mmap(2)), such as libraries.
Shmem %lu (since Linux 2.6.32)
[To be documented.]
Slab %lu
In-kernel data structures cache.
SReclaimable %lu (since Linux 2.6.19)
Part of Slab, that might be reclaimed, such as caches.
SUnreclaim %lu (since Linux 2.6.19)
Part of Slab, that cannot be reclaimed on memory pressure.
KernelStack %lu (since Linux 2.6.32)
Amount of memory allocated to kernel stacks.
PageTables %lu (since Linux 2.6.18)
Amount of memory dedicated to the lowest level of page tables.
Quicklists %lu (since Linux 2.6.27)
(CONFIG_QUICKLIST is required.) [To be documented.]
NFS_Unstable %lu (since Linux 2.6.18)
NFS pages sent to the server, but not yet committed to stable storage.
Bounce %lu (since Linux 2.6.18)
Memory used for block device "bounce buffers".
WritebackTmp %lu (since Linux 2.6.26)
Memory used by FUSE for temporary writeback buffers.
CommitLimit %lu (since Linux 2.6.10)
This is the total amount of memory currently available to be allocated on
the system, expressed in kilobytes. This limit is adhered to only if strict
overcommit accounting is enabled (mode 2 in /proc/sys/vm/overcommit_memory).
The limit is calculated according to the formula described under
/proc/sys/vm/overcommit_memory. For further details, see the kernel source
file Documentation/vm/overcommit-accounting.
Committed_AS %lu
The amount of memory presently allocated on the system. The committed
memory is a sum of all of the memory which has been allocated by processes,
even if it has not been "used" by them as of yet. A process which allocates
1GB of memory (using malloc(3) or similar), but touches only 300MB of that
memory will show up as using only 300MB of memory even if it has the address
space allocated for the entire 1GB.
This 1GB is memory which has been "committed" to by the VM and can be used
at any time by the allocating application. With strict overcommit enabled
on the system (mode 2 in IR /proc/sys/vm/overcommit_memory ), allocations
which would exceed the CommitLimit will not be permitted. This is useful if
one needs to guarantee that processes will not fail due to lack of memory
once that memory has been successfully allocated.
VmallocTotal %lu
Total size of vmalloc memory area.
VmallocUsed %lu
Amount of vmalloc area which is used.
VmallocChunk %lu
Largest contiguous block of vmalloc area which is free.
HardwareCorrupted %lu (since Linux 2.6.32)
(CONFIG_MEMORY_FAILURE is required.) [To be documented.]
AnonHugePages %lu (since Linux 2.6.38)
(CONFIG_TRANSPARENT_HUGEPAGE is required.) Non-file backed huge pages
mapped into user-space page tables.
HugePages_Total %lu
(CONFIG_HUGETLB_PAGE is required.) The size of the pool of huge pages.
HugePages_Free %lu
(CONFIG_HUGETLB_PAGE is required.) The number of huge pages in the pool
that are not yet allocated.
HugePages_Rsvd %lu (since Linux 2.6.17)
(CONFIG_HUGETLB_PAGE is required.) This is the number of huge pages for
which a commitment to allocate from the pool has been made, but no
allocation has yet been made. These reserved huge pages guarantee that an
application will be able to allocate a huge page from the pool of huge pages
at fault time.
HugePages_Surp %lu (since Linux 2.6.24)
(CONFIG_HUGETLB_PAGE is required.) This is the number of huge pages in the
pool above the value in /proc/sys/vm/nr_hugepages. The maximum number of
surplus huge pages is controlled by /proc/sys/vm/nr_overcommit_hugepages.
Hugepagesize %lu
(CONFIG_HUGETLB_PAGE is required.) The size of huge pages.
/proc/modules
A text list of the modules that have been loaded by the system. See also lsmod(8).
/proc/mounts
Before kernel 2.4.19, this file was a list of all the filesystems currently mounted
on the system. With the introduction of per-process mount namespaces in Linux
2.4.19, this file became a link to /proc/self/mounts, which lists the mount points
of the process's own mount namespace. The format of this file is documented in
fstab(5).
/proc/mtrr
Memory Type Range Registers. See the Linux kernel source file
Documentation/mtrr.txt for details.
/proc/net
various net pseudo-files, all of which give the status of some part of the
networking layer. These files contain ASCII structures and are, therefore,
readable with cat(1). However, the standard netstat(8) suite provides much cleaner
access to these files.
/proc/net/arp
This holds an ASCII readable dump of the kernel ARP table used for address
resolutions. It will show both dynamically learned and preprogrammed ARP entries.
The format is:
IP address HW type Flags HW address Mask Device
192.168.0.50 0x1 0x2 00:50:BF:25:68:F3 * eth0
192.168.0.250 0x1 0xc 00:00:00:00:00:00 * eth0
Here "IP address" is the IPv4 address of the machine and the "HW type" is the
hardware type of the address from RFC 826. The flags are the internal flags of the
ARP structure (as defined in /usr/include/linux/if_arp.h) and the "HW address" is
the data link layer mapping for that IP address if it is known.
/proc/net/dev
The dev pseudo-file contains network device status information. This gives the
number of received and sent packets, the number of errors and collisions and other
basic statistics. These are used by the ifconfig(8) program to report device
status. The format is:
Inter-| Receive | Transmit
face |bytes packets errs drop fifo frame compressed multicast|bytes packets errs drop fifo colls carrier compressed
lo: 2776770 11307 0 0 0 0 0 0 2776770 11307 0 0 0 0 0 0
eth0: 1215645 2751 0 0 0 0 0 0 1782404 4324 0 0 0 427 0 0
ppp0: 1622270 5552 1 0 0 0 0 0 354130 5669 0 0 0 0 0 0
tap0: 7714 81 0 0 0 0 0 0 7714 81 0 0 0 0 0 0
/proc/net/dev_mcast
Defined in /usr/src/linux/net/core/dev_mcast.c:
indx interface_name dmi_u dmi_g dmi_address
2 eth0 1 0 01005e000001
3 eth1 1 0 01005e000001
4 eth2 1 0 01005e000001
/proc/net/igmp
Internet Group Management Protocol. Defined in /usr/src/linux/net/core/igmp.c.
/proc/net/rarp
This file uses the same format as the arp file and contains the current reverse
mapping database used to provide rarp(8) reverse address lookup services. If RARP
is not configured into the kernel, this file will not be present.
/proc/net/raw
Holds a dump of the RAW socket table. Much of the information is not of use apart
from debugging. The "sl" value is the kernel hash slot for the socket, the
"local_address" is the local address and protocol number pair. "St" is the
internal status of the socket. The "tx_queue" and "rx_queue" are the outgoing and
incoming data queue in terms of kernel memory usage. The "tr", "tm->when", and
"rexmits" fields are not used by RAW. The "uid" field holds the effective UID of
the creator of the socket.
/proc/net/snmp
This file holds the ASCII data needed for the IP, ICMP, TCP, and UDP management
information bases for an SNMP agent.
/proc/net/tcp
Holds a dump of the TCP socket table. Much of the information is not of use apart
from debugging. The "sl" value is the kernel hash slot for the socket, the
"local_address" is the local address and port number pair. The "rem_address" is
the remote address and port number pair (if connected). "St" is the internal
status of the socket. The "tx_queue" and "rx_queue" are the outgoing and incoming
data queue in terms of kernel memory usage. The "tr", "tm->when", and "rexmits"
fields hold internal information of the kernel socket state and are useful only for
debugging. The "uid" field holds the effective UID of the creator of the socket.
/proc/net/udp
Holds a dump of the UDP socket table. Much of the information is not of use apart
from debugging. The "sl" value is the kernel hash slot for the socket, the
"local_address" is the local address and port number pair. The "rem_address" is
the remote address and port number pair (if connected). "St" is the internal
status of the socket. The "tx_queue" and "rx_queue" are the outgoing and incoming
data queue in terms of kernel memory usage. The "tr", "tm->when", and "rexmits"
fields are not used by UDP. The "uid" field holds the effective UID of the creator
of the socket. The format is:
sl local_address rem_address st tx_queue rx_queue tr rexmits tm->when uid
1: 01642C89:0201 0C642C89:03FF 01 00000000:00000001 01:000071BA 00000000 0
1: 00000000:0801 00000000:0000 0A 00000000:00000000 00:00000000 6F000100 0
1: 00000000:0201 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0
/proc/net/unix
Lists the UNIX domain sockets present within the system and their status. The
format is:
Num RefCount Protocol Flags Type St Path
0: 00000002 00000000 00000000 0001 03
1: 00000001 00000000 00010000 0001 01 /dev/printer
The fields are as follows:
Num: the kernel table slot number.
RefCount: the number of users of the socket.
Protocol: currently always 0.
Flags: the internal kernel flags holding the status of the socket.
Type: the socket type. For SOCK_STREAM sockets, this is 0001; for SOCK_DGRAM
sockets, it is 0002; and for SOCK_SEQPACKET sockets, it is 0005.
St: the internal state of the socket.
Path: the bound path (if any) of the socket. Sockets in the abstract namespace
are included in the list, and are shown with a Path that commences with
the character '@'.
/proc/net/netfilter/nfnetlink_queue
This file contains information about netfilter userspace queueing, if used. Each
line represents a queue. Queues that have not been subscribed to by userspace are
not shown.
1 4207 0 2 65535 0 0 0 1
(1) (2) (3)(4) (5) (6) (7) (8)
The fields in each line are:
(1) The ID of the queue. This matches what is specified in the --queue-num or
--queue-balance options to the iptables(8) NFQUEUE target. See iptables-
extensions(8) for more information.
(2) The netlink port ID subscribed to the queue.
(3) The number of packets currently queued and waiting to be processed by the
application.
(4) The copy mode of the queue. It is either 1 (metadata only) or 2 (also copy
payload data to userspace).
(5) Copy range; that is, how many bytes of packet payload should be copied to
userspace at most.
(6) queue dropped. Number of packets that had to be dropped by the kernel because
too many packets are already waiting for userspace to send back the mandatory
accept/drop verdicts.
(7) queue user dropped. Number of packets that were dropped within the netlink
subsystem. Such drops usually happen when the corresponding socket buffer is
full; that is, userspace is not able to read messages fast enough.
(8) sequence number. Every queued packet is associated with a (32-bit)
monotonically-increasing sequence number. This shows the ID of the most
recent packet queued.
The last number exists only for compatibility reasons and is always 1.
/proc/partitions
Contains the major and minor numbers of each partition as well as the number of
1024-byte blocks and the partition name.
/proc/pci
This is a listing of all PCI devices found during kernel initialization and their
configuration.
This file has been deprecated in favor of a new /proc interface for PCI
(/proc/bus/pci). It became optional in Linux 2.2 (available with
CONFIG_PCI_OLD_PROC set at kernel compilation). It became once more nonoptionally
enabled in Linux 2.4. Next, it was deprecated in Linux 2.6 (still available with
CONFIG_PCI_LEGACY_PROC set), and finally removed altogether since Linux 2.6.17.
/proc/profile (since Linux 2.4)
This file is present only if the kernel was booted with the profile=1 command-line
option. It exposes kernel profiling information in a binary format for use by
readprofile(1). Writing (e.g., an empty string) to this file resets the profiling
counters; on some architectures, writing a binary integer "profiling multiplier" of
size sizeof(int) sets the profiling interrupt frequency.
/proc/scsi
A directory with the scsi mid-level pseudo-file and various SCSI low-level driver
directories, which contain a file for each SCSI host in this system, all of which
give the status of some part of the SCSI IO subsystem. These files contain ASCII
structures and are, therefore, readable with cat(1).
You can also write to some of the files to reconfigure the subsystem or switch
certain features on or off.
/proc/scsi/scsi
This is a listing of all SCSI devices known to the kernel. The listing is similar
to the one seen during bootup. scsi currently supports only the add-single-device
command which allows root to add a hotplugged device to the list of known devices.
The command
echo 'scsi add-single-device 1 0 5 0' > /proc/scsi/scsi
will cause host scsi1 to scan on SCSI channel 0 for a device on ID 5 LUN 0. If
there is already a device known on this address or the address is invalid, an error
will be returned.
/proc/scsi/[drivername]
[drivername] can currently be NCR53c7xx, aha152x, aha1542, aha1740, aic7xxx,
buslogic, eata_dma, eata_pio, fdomain, in2000, pas16, qlogic, scsi_debug, seagate,
t128, u15-24f, ultrastore, or wd7000. These directories show up for all drivers
that registered at least one SCSI HBA. Every directory contains one file per
registered host. Every host-file is named after the number the host was assigned
during initialization.
Reading these files will usually show driver and host configuration, statistics,
and so on.
Writing to these files allows different things on different hosts. For example,
with the latency and nolatency commands, root can switch on and off command latency
measurement code in the eata_dma driver. With the lockup and unlock commands, root
can control bus lockups simulated by the scsi_debug driver.
/proc/self
This directory refers to the process accessing the /proc filesystem, and is
identical to the /proc directory named by the process ID of the same process.
/proc/slabinfo
Information about kernel caches. Since Linux 2.6.16 this file is present only if
the CONFIG_SLAB kernel configuration option is enabled. The columns in
/proc/slabinfo are:
cache-name
num-active-objs
total-objs
object-size
num-active-slabs
total-slabs
num-pages-per-slab
See slabinfo(5) for details.
/proc/stat
kernel/system statistics. Varies with architecture. Common entries include:
cpu 3357 0 4313 1362393
The amount of time, measured in units of USER_HZ (1/100ths of a second on
most architectures, use sysconf(_SC_CLK_TCK) to obtain the right value),
that the system spent in various states:
user (1) Time spent in user mode.
nice (2) Time spent in user mode with low priority (nice).
system (3) Time spent in system mode.
idle (4) Time spent in the idle task. This value should be USER_HZ times
the second entry in the /proc/uptime pseudo-file.
iowait (since Linux 2.5.41)
(5) Time waiting for I/O to complete.
irq (since Linux 2.6.0-test4)
(6) Time servicing interrupts.
softirq (since Linux 2.6.0-test4)
(7) Time servicing softirqs.
steal (since Linux 2.6.11)
(8) Stolen time, which is the time spent in other operating systems
when running in a virtualized environment
guest (since Linux 2.6.24)
(9) Time spent running a virtual CPU for guest operating systems
under the control of the Linux kernel.
guest_nice (since Linux 2.6.33)
(10) Time spent running a niced guest (virtual CPU for guest
operating systems under the control of the Linux kernel).
page 5741 1808
The number of pages the system paged in and the number that were paged out
(from disk).
swap 1 0
The number of swap pages that have been brought in and out.
intr 1462898
This line shows counts of interrupts serviced since boot time, for each of
the possible system interrupts. The first column is the total of all
interrupts serviced including unnumbered architecture specific interrupts;
each subsequent column is the total for that particular numbered interrupt.
Unnumbered interrupts are not shown, only summed into the total.
disk_io: (2,0):(31,30,5764,1,2) (3,0):...
(major,disk_idx):(noinfo, read_io_ops, blks_read, write_io_ops,
blks_written)
(Linux 2.4 only)
ctxt 115315
The number of context switches that the system underwent.
btime 769041601
boot time, in seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
processes 86031
Number of forks since boot.
procs_running 6
Number of processes in runnable state. (Linux 2.5.45 onward.)
procs_blocked 2
Number of processes blocked waiting for I/O to complete. (Linux 2.5.45
onward.)
/proc/swaps
Swap areas in use. See also swapon(8).
/proc/sys
This directory (present since 1.3.57) contains a number of files and subdirectories
corresponding to kernel variables. These variables can be read and sometimes
modified using the /proc filesystem, and the (deprecated) sysctl(2) system call.
String values may be terminated by either '\0' or '\n'.
Integer and long values may be written either in decimal or in hexadecimal notation
(e.g. 0x3FFF). When writing multiple integer or long values, these may be
separated by any of the following whitespace characters: ' ', '\t', or '\n'. Using
other separators leads to the error EINVAL.
/proc/sys/abi (since Linux 2.4.10)
This directory may contain files with application binary information. See the
Linux kernel source file Documentation/sysctl/abi.txt for more information.
/proc/sys/debug
This directory may be empty.
/proc/sys/dev
This directory contains device-specific information (e.g., dev/cdrom/info). On
some systems, it may be empty.
/proc/sys/fs
This directory contains the files and subdirectories for kernel variables related
to filesystems.
/proc/sys/fs/binfmt_misc
Documentation for files in this directory can be found in the Linux kernel sources
in Documentation/binfmt_misc.txt.
/proc/sys/fs/dentry-state (since Linux 2.2)
This file contains information about the status of the directory cache (dcache).
The file contains six numbers, nr_dentry, nr_unused, age_limit (age in seconds),
want_pages (pages requested by system) and two dummy values.
* nr_dentry is the number of allocated dentries (dcache entries). This field is
unused in Linux 2.2.
* nr_unused is the number of unused dentries.
* age_limit is the age in seconds after which dcache entries can be reclaimed when
memory is short.
* want_pages is nonzero when the kernel has called shrink_dcache_pages() and the
dcache isn't pruned yet.
/proc/sys/fs/dir-notify-enable
This file can be used to disable or enable the dnotify interface described in
fcntl(2) on a system-wide basis. A value of 0 in this file disables the interface,
and a value of 1 enables it.
/proc/sys/fs/dquot-max
This file shows the maximum number of cached disk quota entries. On some (2.4)
systems, it is not present. If the number of free cached disk quota entries is
very low and you have some awesome number of simultaneous system users, you might
want to raise the limit.
/proc/sys/fs/dquot-nr
This file shows the number of allocated disk quota entries and the number of free
disk quota entries.
/proc/sys/fs/epoll (since Linux 2.6.28)
This directory contains the file max_user_watches, which can be used to limit the
amount of kernel memory consumed by the epoll interface. For further details, see
epoll(7).
/proc/sys/fs/file-max
This file defines a system-wide limit on the number of open files for all
processes. System calls that fail when encountering this limit fail with the error
ENFILE. (See also setrlimit(2), which can be used by a process to set the per-
process limit, RLIMIT_NOFILE, on the number of files it may open.) If you get lots
of error messages in the kernel log about running out of file handles (look for
"VFS: file-max limit <number> reached"), try increasing this value:
echo 100000 > /proc/sys/fs/file-max
Privileged processes (CAP_SYS_ADMIN) can override the file-max limit.
/proc/sys/fs/file-nr
This (read-only) file contains three numbers: the number of allocated file handles
(i.e., the number of files presently opened); the number of free file handles; and
the maximum number of file handles (i.e., the same value as /proc/sys/fs/file-max).
If the number of allocated file handles is close to the maximum, you should
consider increasing the maximum. Before Linux 2.6, the kernel allocated file
handles dynamically, but it didn't free them again. Instead the free file handles
were kept in a list for reallocation; the "free file handles" value indicates the
size of that list. A large number of free file handles indicates that there was a
past peak in the usage of open file handles. Since Linux 2.6, the kernel does
deallocate freed file handles, and the "free file handles" value is always zero.
/proc/sys/fs/inode-max (only present until Linux 2.2)
This file contains the maximum number of in-memory inodes. This value should be
3-4 times larger than the value in file-max, since stdin, stdout and network
sockets also need an inode to handle them. When you regularly run out of inodes,
you need to increase this value.
Starting with Linux 2.4, there is no longer a static limit on the number of inodes,
and this file is removed.
/proc/sys/fs/inode-nr
This file contains the first two values from inode-state.
/proc/sys/fs/inode-state
This file contains seven numbers: nr_inodes, nr_free_inodes, preshrink, and four
dummy values (always zero).
nr_inodes is the number of inodes the system has allocated. nr_free_inodes
represents the number of free inodes.
preshrink is nonzero when the nr_inodes > inode-max and the system needs to prune
the inode list instead of allocating more; since Linux 2.4, this field is a dummy
value (always zero).
/proc/sys/fs/inotify (since Linux 2.6.13)
This directory contains files max_queued_events, max_user_instances, and
max_user_watches, that can be used to limit the amount of kernel memory consumed by
the inotify interface. For further details, see inotify(7).
/proc/sys/fs/lease-break-time
This file specifies the grace period that the kernel grants to a process holding a
file lease (fcntl(2)) after it has sent a signal to that process notifying it that
another process is waiting to open the file. If the lease holder does not remove
or downgrade the lease within this grace period, the kernel forcibly breaks the
lease.
/proc/sys/fs/leases-enable
This file can be used to enable or disable file leases (fcntl(2)) on a system-wide
basis. If this file contains the value 0, leases are disabled. A nonzero value
enables leases.
/proc/sys/fs/mqueue (since Linux 2.6.6)
This directory contains files msg_max, msgsize_max, and queues_max, controlling the
resources used by POSIX message queues. See mq_overview(7) for details.
/proc/sys/fs/nr_open (since Linux 2.6.25)
This file imposes ceiling on the value to which the RLIMIT_NOFILE resource limit
can be raised (see getrlimit(2)). This ceiling is enforced for both unprivileged
and privileged process. The default value in this file is 1048576. (Before Linux
2.6.25, the ceiling for RLIMIT_NOFILE was hard-coded to the same value.)
/proc/sys/fs/overflowgid and /proc/sys/fs/overflowuid
These files allow you to change the value of the fixed UID and GID. The default is
65534. Some filesystems support only 16-bit UIDs and GIDs, although in Linux UIDs
and GIDs are 32 bits. When one of these filesystems is mounted with writes
enabled, any UID or GID that would exceed 65535 is translated to the overflow value
before being written to disk.
/proc/sys/fs/pipe-max-size (since Linux 2.6.35)
The value in this file defines an upper limit for raising the capacity of a pipe
using the fcntl(2) F_SETPIPE_SZ operation. This limit applies only to unprivileged
processes. The default value for this file is 1,048,576. The value assigned to
this file may be rounded upward, to reflect the value actually employed for a
convenient implementation. To determine the rounded-up value, display the contents
of this file after assigning a value to it. The minimum value that can be assigned
to this file is the system page size.
/proc/sys/fs/protected_hardlinks (since Linux 3.6)
When the value in this file is 0, no restrictions are placed on the creation of
hard links (i.e., this is the historical behavior before Linux 3.6). When the
value in this file is 1, a hard link can be created to a target file only if one of
the following conditions is true:
* The caller has the CAP_FOWNER capability.
* The filesystem UID of the process creating the link matches the owner (UID) of
the target file (as described in credentials(7), a process's filesystem UID is
normally the same as its effective UID).
* All of the following conditions are true:
• the target is a regular file;
• the target file does not have its set-user-ID mode bit enabled;
• the target file does not have both its set-group-ID and group-executable
mode bits enabled; and
• the caller has permission to read and write the target file (either via the
file's permissions mask or because it has suitable capabilities).
The default value in this file is 0. Setting the value to 1 prevents a
longstanding class of security issues caused by hard-link-based time-of-check,
time-of-use races, most commonly seen in world-writable directories such as /tmp.
The common method of exploiting this flaw is to cross privilege boundaries when
following a given hard link (i.e., a root process follows a hard link created by
another user). Additionally, on systems without separated partitions, this stops
unauthorized users from "pinning" vulnerable set-user-ID and set-group-ID files
against being upgraded by the administrator, or linking to special files.
/proc/sys/fs/protected_symlinks (since Linux 3.6)
When the value in this file is 0, no restrictions are placed on following symbolic
links (i.e., this is the historical behavior before Linux 3.6). When the value in
this file is 1, symbolic links are followed only in the following circumstances:
* the filesystem UID of the process following the link matches the owner (UID) of
the symbolic link (as described in credentials(7), a process's filesystem UID is
normally the same as its effective UID);
* the link is not in a sticky world-writable directory; or
* the symbolic link and its parent directory have the same owner (UID)
A system call that fails to follow a symbolic link because of the above
restrictions returns the error EACCES in errno.
The default value in this file is 0. Setting the value to 1 avoids a longstanding
class of security issues based on time-of-check, time-of-use races when accessing
symbolic links.
/proc/sys/fs/suid_dumpable (since Linux 2.6.13)
The value in this file is assigned to a process's "dumpable" flag in the
circumstances described in prctl(2). In effect, the value in this file determines
whether core dump files are produced for set-user-ID or otherwise protected/tainted
binaries. Three different integer values can be specified:
0 (default)
This provides the traditional (pre-Linux 2.6.13) behavior. A core dump will
not be produced for a process which has changed credentials (by calling
seteuid(2), setgid(2), or similar, or by executing a set-user-ID or set-
group-ID program) or whose binary does not have read permission enabled.
1 ("debug")
All processes dump core when possible. The core dump is owned by the
filesystem user ID of the dumping process and no security is applied. This
is intended for system debugging situations only. Ptrace is unchecked.
2 ("suidsafe")
Any binary which normally would not be dumped (see "0" above) is dumped
readable by root only. This allows the user to remove the core dump file
but not to read it. For security reasons core dumps in this mode will not
overwrite one another or other files. This mode is appropriate when
administrators are attempting to debug problems in a normal environment.
Additionally, since Linux 3.6, /proc/sys/kernel/core_pattern must either be
an absolute pathname or a pipe command, as detailed in core(5). Warnings
will be written to the kernel log if core_pattern does not follow these
rules, and no core dump will be produced.
/proc/sys/fs/super-max
This file controls the maximum number of superblocks, and thus the maximum number
of mounted filesystems the kernel can have. You need increase only super-max if
you need to mount more filesystems than the current value in super-max allows you
to.
/proc/sys/fs/super-nr
This file contains the number of filesystems currently mounted.
/proc/sys/kernel
This directory contains files controlling a range of kernel parameters, as
described below.
/proc/sys/kernel/acct
This file contains three numbers: highwater, lowwater, and frequency. If BSD-style
process accounting is enabled, these values control its behavior. If free space on
filesystem where the log lives goes below lowwater percent, accounting suspends.
If free space gets above highwater percent, accounting resumes. frequency
determines how often the kernel checks the amount of free space (value is in
seconds). Default values are 4, 2 and 30. That is, suspend accounting if 2% or
less space is free; resume it if 4% or more space is free; consider information
about amount of free space valid for 30 seconds.
/proc/sys/kernel/auto_msgmni (Linux 2.6.27 to 3.18)
From Linux 2.6.27 to 3.18, this file was used to control recomputing of the value
in /proc/sys/kernel/msgmni upon the addition or removal of memory or upon IPC
namespace creation/removal. Echoing "1" into this file enabled msgmni automatic
recomputing (and triggered a recomputation of msgmni based on the current amount of
available memory and number of IPC namespaces). Echoing "0" disabled automatic
recomputing. (Automatic recomputing was also disabled if a value was explicitly
assigned to /proc/sys/kernel/msgmni.) The default value in auto_msgmni was 1.
Since Linux 3.19, the content of this file has no effect (because msgmni defaults
to near the maximum value possible), and reads from this file always return the
value "0".
/proc/sys/kernel/cap_last_cap (since Linux 3.2)
See capabilities(7).
/proc/sys/kernel/cap-bound (from Linux 2.2 to 2.6.24)
This file holds the value of the kernel capability bounding set (expressed as a
signed decimal number). This set is ANDed against the capabilities permitted to a
process during execve(2). Starting with Linux 2.6.25, the system-wide capability
bounding set disappeared, and was replaced by a per-thread bounding set; see
capabilities(7).
/proc/sys/kernel/core_pattern
See core(5).
/proc/sys/kernel/core_uses_pid
See core(5).
/proc/sys/kernel/ctrl-alt-del
This file controls the handling of Ctrl-Alt-Del from the keyboard. When the value
in this file is 0, Ctrl-Alt-Del is trapped and sent to the init(1) program to
handle a graceful restart. When the value is greater than zero, Linux's reaction
to a Vulcan Nerve Pinch (tm) will be an immediate reboot, without even syncing its
dirty buffers. Note: when a program (like dosemu) has the keyboard in "raw" mode,
the ctrl-alt-del is intercepted by the program before it ever reaches the kernel
tty layer, and it's up to the program to decide what to do with it.
/proc/sys/kernel/dmesg_restrict (since Linux 2.6.37)
The value in this file determines who can see kernel syslog contents. A value of 0
in this file imposes no restrictions. If the value is 1, only privileged users can
read the kernel syslog. (See syslog(2) for more details.) Since Linux 3.4, only
users with the CAP_SYS_ADMIN capability may change the value in this file.
/proc/sys/kernel/domainname and /proc/sys/kernel/hostname
can be used to set the NIS/YP domainname and the hostname of your box in exactly
the same way as the commands domainname(1) and hostname(1), that is:
# echo 'darkstar' > /proc/sys/kernel/hostname
# echo 'mydomain' > /proc/sys/kernel/domainname
has the same effect as
# hostname 'darkstar'
# domainname 'mydomain'
Note, however, that the classic darkstar.frop.org has the hostname "darkstar" and
DNS (Internet Domain Name Server) domainname "frop.org", not to be confused with
the NIS (Network Information Service) or YP (Yellow Pages) domainname. These two
domain names are in general different. For a detailed discussion see the
hostname(1) man page.
/proc/sys/kernel/hotplug
This file contains the path for the hotplug policy agent. The default value in
this file is /sbin/hotplug.
/proc/sys/kernel/htab-reclaim
(PowerPC only) If this file is set to a nonzero value, the PowerPC htab (see kernel
file Documentation/powerpc/ppc_htab.txt) is pruned each time the system hits the
idle loop.
/proc/sys/kernel/kptr_restrict (since Linux 2.6.38)
The value in this file determines whether kernel addresses are exposed via /proc
files and other interfaces. A value of 0 in this file imposes no restrictions. If
the value is 1, kernel pointers printed using the %pK format specifier will be
replaced with zeros unless the user has the CAP_SYSLOG capability. If the value is
2, kernel pointers printed using the %pK format specifier will be replaced with
zeros regardless of the user's capabilities. The initial default value for this
file was 1, but the default was changed to 0 in Linux 2.6.39. Since Linux 3.4,
only users with the CAP_SYS_ADMIN capability can change the value in this file.
/proc/sys/kernel/l2cr
(PowerPC only) This file contains a flag that controls the L2 cache of G3 processor
boards. If 0, the cache is disabled. Enabled if nonzero.
/proc/sys/kernel/modprobe
This file contains the path for the kernel module loader. The default value is
/sbin/modprobe. The file is present only if the kernel is built with the
CONFIG_MODULES (CONFIG_KMOD in Linux 2.6.26 and earlier) option enabled. It is
described by the Linux kernel source file Documentation/kmod.txt (present only in
kernel 2.4 and earlier).
/proc/sys/kernel/modules_disabled (since Linux 2.6.31)
A toggle value indicating if modules are allowed to be loaded in an otherwise
modular kernel. This toggle defaults to off (0), but can be set true (1). Once
true, modules can be neither loaded nor unloaded, and the toggle cannot be set back
to false. The file is present only if the kernel is built with the CONFIG_MODULES
option enabled.
/proc/sys/kernel/msgmax (since Linux 2.2)
This file defines a system-wide limit specifying the maximum number of bytes in a
single message written on a System V message queue.
/proc/sys/kernel/msgmni (since Linux 2.4)
This file defines the system-wide limit on the number of message queue identifiers.
See also /proc/sys/kernel/auto_msgmni.
/proc/sys/kernel/msgmnb (since Linux 2.2)
This file defines a system-wide parameter used to initialize the msg_qbytes setting
for subsequently created message queues. The msg_qbytes setting specifies the
maximum number of bytes that may be written to the message queue.
/proc/sys/kernel/ngroups_max (since Linux 2.6.4)
This is a read-only file that displays the upper limit on the number of a process's
group memberships.
/proc/sys/kernel/ostype and /proc/sys/kernel/osrelease
These files give substrings of /proc/version.
/proc/sys/kernel/overflowgid and /proc/sys/kernel/overflowuid
These files duplicate the files /proc/sys/fs/overflowgid and
/proc/sys/fs/overflowuid.
/proc/sys/kernel/panic
This file gives read/write access to the kernel variable panic_timeout. If this is
zero, the kernel will loop on a panic; if nonzero, it indicates that the kernel
should autoreboot after this number of seconds. When you use the software watchdog
device driver, the recommended setting is 60.
/proc/sys/kernel/panic_on_oops (since Linux 2.5.68)
This file controls the kernel's behavior when an oops or BUG is encountered. If
this file contains 0, then the system tries to continue operation. If it contains
1, then the system delays a few seconds (to give klogd time to record the oops
output) and then panics. If the /proc/sys/kernel/panic file is also nonzero, then
the machine will be rebooted.
/proc/sys/kernel/pid_max (since Linux 2.5.34)
This file specifies the value at which PIDs wrap around (i.e., the value in this
file is one greater than the maximum PID). PIDs greater than this value are not
allocated; thus, the value in this file also acts as a system-wide limit on the
total number of processes and threads. The default value for this file, 32768,
results in the same range of PIDs as on earlier kernels. On 32-bit platforms,
32768 is the maximum value for pid_max. On 64-bit systems, pid_max can be set to
any value up to 2^22 (PID_MAX_LIMIT, approximately 4 million).
/proc/sys/kernel/powersave-nap (PowerPC only)
This file contains a flag. If set, Linux-PPC will use the "nap" mode of
powersaving, otherwise the "doze" mode will be used.
/proc/sys/kernel/printk
See syslog(2).
/proc/sys/kernel/pty (since Linux 2.6.4)
This directory contains two files relating to the number of UNIX 98 pseudoterminals
(see pts(4)) on the system.
/proc/sys/kernel/pty/max
This file defines the maximum number of pseudoterminals.
/proc/sys/kernel/pty/nr
This read-only file indicates how many pseudoterminals are currently in use.
/proc/sys/kernel/random
This directory contains various parameters controlling the operation of the file
/dev/random. See random(4) for further information.
/proc/sys/kernel/random/uuid (since Linux 2.4)
Each read from this read-only file returns a randomly generated 128-bit UUID, as a
string in the standard UUID format.
/proc/sys/kernel/randomize_va_space (since Linux 2.6.12)
Select the address space layout randomization (ASLR) policy for the system (on
architectures that support ASLR). Three values are supported for this file:
0 Turn ASLR off. This is the default for architectures that don't support ASLR,
and when the kernel is booted with the norandmaps parameter.
1 Make the addresses of mmap(2) allocations, the stack, and the VDSO page
randomized. Among other things, this means that shared libraries will be loaded
at randomized addresses. The text segment of PIE-linked binaries will also be
loaded at a randomized address. This value is the default if the kernel was
configured with CONFIG_COMPAT_BRK.
2 (Since Linux 2.6.25) Also support heap randomization. This value is the default
if the kernel was not configured with CONFIG_COMPAT_BRK.
/proc/sys/kernel/real-root-dev
This file is documented in the Linux kernel source file Documentation/initrd.txt.
/proc/sys/kernel/reboot-cmd (Sparc only)
This file seems to be a way to give an argument to the SPARC ROM/Flash boot loader.
Maybe to tell it what to do after rebooting?
/proc/sys/kernel/rtsig-max
(Only in kernels up to and including 2.6.7; see setrlimit(2)) This file can be used
to tune the maximum number of POSIX real-time (queued) signals that can be
outstanding in the system.
/proc/sys/kernel/rtsig-nr
(Only in kernels up to and including 2.6.7.) This file shows the number POSIX
real-time signals currently queued.
/proc/sys/kernel/sched_rr_timeslice_ms (since Linux 3.9)
See sched_rr_get_interval(2).
/proc/sys/kernel/sched_rt_period_us (Since Linux 2.6.25)
See sched(7).
/proc/sys/kernel/sched_rt_runtime_us (Since Linux 2.6.25)
See sched(7).
/proc/sys/kernel/sem (since Linux 2.4)
This file contains 4 numbers defining limits for System V IPC semaphores. These
fields are, in order:
SEMMSL The maximum semaphores per semaphore set.
SEMMNS A system-wide limit on the number of semaphores in all semaphore sets.
SEMOPM The maximum number of operations that may be specified in a semop(2) call.
SEMMNI A system-wide limit on the maximum number of semaphore identifiers.
/proc/sys/kernel/sg-big-buff
This file shows the size of the generic SCSI device (sg) buffer. You can't tune it
just yet, but you could change it at compile time by editing include/scsi/sg.h and
changing the value of SG_BIG_BUFF. However, there shouldn't be any reason to
change this value.
/proc/sys/kernel/shm_rmid_forced (since Linux 3.1)
If this file is set to 1, all System V shared memory segments will be marked for
destruction as soon as the number of attached processes falls to zero; in other
words, it is no longer possible to create shared memory segments that exist
independently of any attached process.
The effect is as though a shmctl(2) IPC_RMID is performed on all existing segments
as well as all segments created in the future (until this file is reset to 0).
Note that existing segments that are attached to no process will be immediately
destroyed when this file is set to 1. Setting this option will also destroy
segments that were created, but never attached, upon termination of the process
that created the segment with shmget(2).
Setting this file to 1 provides a way of ensuring that all System V shared memory
segments are counted against the resource usage and resource limits (see the
description of RLIMIT_AS in getrlimit(2)) of at least one process.
Because setting this file to 1 produces behavior that is nonstandard and could also
break existing applications, the default value in this file is 0. Only set this
file to 1 if you have a good understanding of the semantics of the applications
using System V shared memory on your system.
/proc/sys/kernel/shmall (since Linux 2.2)
This file contains the system-wide limit on the total number of pages of System V
shared memory.
/proc/sys/kernel/shmmax (since Linux 2.2)
This file can be used to query and set the run-time limit on the maximum (System V
IPC) shared memory segment size that can be created. Shared memory segments up to
1GB are now supported in the kernel. This value defaults to SHMMAX.
/proc/sys/kernel/shmmni (since Linux 2.4)
This file specifies the system-wide maximum number of System V shared memory
segments that can be created.
/proc/sys/kernel/sysctl_writes_strict (since Linux 3.16)
The value in this file determines how the file offset affects the behavior of
updating entries in files under /proc/sys. The file has three possible values:
-1 This provides legacy handling, with no printk warnings. Each write(2) must
fully contain the value to be written, and multiple writes on the same file
descriptor will overwrite the entire value, regardless of the file position.
0 (default) This provides the same behavior as for -1, but printk warnings are
written for processes that perform writes when the file offset is not 0.
1 Respect the file offset when writing strings into /proc/sys files. Multiple
writes will append to the value buffer. Anything written beyond the maximum
length of the value buffer will be ignored. Writes to numeric /proc/sys
entries must always be at file offset 0 and the value must be fully contained
in the buffer provided to write(2).
/proc/sys/kernel/sysrq
This file controls the functions allowed to be invoked by the SysRq key. By
default, the file contains 1 meaning that every possible SysRq request is allowed
(in older kernel versions, SysRq was disabled by default, and you were required to
specifically enable it at run-time, but this is not the case any more). Possible
values in this file are:
0 Disable sysrq completely
1 Enable all functions of sysrq
> 1 Bit mask of allowed sysrq functions, as follows:
2 Enable control of console logging level
4 Enable control of keyboard (SAK, unraw)
8 Enable debugging dumps of processes etc.
16 Enable sync command
32 Enable remount read-only
64 Enable signaling of processes (term, kill, oom-kill)
128 Allow reboot/poweroff
256 Allow nicing of all real-time tasks
This file is present only if the CONFIG_MAGIC_SYSRQ kernel configuration option is
enabled. For further details see the Linux kernel source file
Documentation/sysrq.txt.
/proc/sys/kernel/version
This file contains a string such as:
#5 Wed Feb 25 21:49:24 MET 1998
The "#5" means that this is the fifth kernel built from this source base and the
date following it indicates the time the kernel was built.
/proc/sys/kernel/threads-max (since Linux 2.3.11)
This file specifies the system-wide limit on the number of threads (tasks) that can
be created on the system.
Since Linux 4.1, the value that can be written to threads-max is bounded. The
minimum value that can be written is 20. The maximum value that can be written is
given by the constant FUTEX_TID_MASK (0x3fffffff). If a value outside of this
range is written to threads-max, the error EINVAL occurs.
The value written is checked against the available RAM pages. If the thread
structures would occupy too much (more than 1/8th) of the available RAM pages,
threads-max is reduced accordingly.
/proc/sys/kernel/yama/ptrace_scope (since Linux 3.5)
See ptrace(2).
/proc/sys/kernel/zero-paged (PowerPC only)
This file contains a flag. When enabled (nonzero), Linux-PPC will pre-zero pages
in the idle loop, possibly speeding up get_free_pages.
/proc/sys/net
This directory contains networking stuff. Explanations for some of the files under
this directory can be found in tcp(7) and ip(7).
/proc/sys/net/core/bpf_jit_enable
See bpf(2).
/proc/sys/net/core/somaxconn
This file defines a ceiling value for the backlog argument of listen(2); see the
listen(2) manual page for details.
/proc/sys/proc
This directory may be empty.
/proc/sys/sunrpc
This directory supports Sun remote procedure call for network filesystem (NFS). On
some systems, it is not present.
/proc/sys/vm
This directory contains files for memory management tuning, buffer and cache
management.
/proc/sys/vm/compact_memory (since Linux 2.6.35)
When 1 is written to this file, all zones are compacted such that free memory is
available in contiguous blocks where possible. The effect of this action can be
seen by examining /proc/buddyinfo.
Only present if the kernel was configured with CONFIG_COMPACTION.
/proc/sys/vm/drop_caches (since Linux 2.6.16)
Writing to this file causes the kernel to drop clean caches, dentries, and inodes
from memory, causing that memory to become free. This can be useful for memory
management testing and performing reproducible filesystem benchmarks. Because
writing to this file causes the benefits of caching to be lost, it can degrade
overall system performance.
To free pagecache, use:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes, use:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes, use:
echo 3 > /proc/sys/vm/drop_caches
Because writing to this file is a nondestructive operation and dirty objects are
not freeable, the user should run sync(1) first.
/proc/sys/vm/legacy_va_layout (since Linux 2.6.9)
If nonzero, this disables the new 32-bit memory-mapping layout; the kernel will use
the legacy (2.4) layout for all processes.
/proc/sys/vm/memory_failure_early_kill (since Linux 2.6.32)
Control how to kill processes when an uncorrected memory error (typically a 2-bit
error in a memory module) that cannot be handled by the kernel is detected in the
background by hardware. In some cases (like the page still having a valid copy on
disk), the kernel will handle the failure transparently without affecting any
applications. But if there is no other up-to-date copy of the data, it will kill
processes to prevent any data corruptions from propagating.
The file has one of the following values:
1: Kill all processes that have the corrupted-and-not-reloadable page mapped as
soon as the corruption is detected. Note this is not supported for a few types
of pages, like kernel internally allocated data or the swap cache, but works
for the majority of user pages.
0: Only unmap the corrupted page from all processes and kill only a process that
tries to access it.
The kill is performed using a SIGBUS signal with si_code set to BUS_MCEERR_AO.
Processes can handle this if they want to; see sigaction(2) for more details.
This feature is active only on architectures/platforms with advanced machine check
handling and depends on the hardware capabilities.
Applications can override the memory_failure_early_kill setting individually with
the prctl(2) PR_MCE_KILL operation.
Only present if the kernel was configured with CONFIG_MEMORY_FAILURE.
/proc/sys/vm/memory_failure_recovery (since Linux 2.6.32)
Enable memory failure recovery (when supported by the platform)
1: Attempt recovery.
0: Always panic on a memory failure.
Only present if the kernel was configured with CONFIG_MEMORY_FAILURE.
/proc/sys/vm/oom_dump_tasks (since Linux 2.6.25)
Enables a system-wide task dump (excluding kernel threads) to be produced when the
kernel performs an OOM-killing. The dump includes the following information for
each task (thread, process): thread ID, real user ID, thread group ID (process ID),
virtual memory size, resident set size, the CPU that the task is scheduled on,
oom_adj score (see the description of /proc/[pid]/oom_adj), and command name. This
is helpful to determine why the OOM-killer was invoked and to identify the rogue
task that caused it.
If this contains the value zero, this information is suppressed. On very large
systems with thousands of tasks, it may not be feasible to dump the memory state
information for each one. Such systems should not be forced to incur a performance
penalty in OOM situations when the information may not be desired.
If this is set to nonzero, this information is shown whenever the OOM-killer
actually kills a memory-hogging task.
The default value is 0.
/proc/sys/vm/oom_kill_allocating_task (since Linux 2.6.24)
This enables or disables killing the OOM-triggering task in out-of-memory
situations.
If this is set to zero, the OOM-killer will scan through the entire tasklist and
select a task based on heuristics to kill. This normally selects a rogue memory-
hogging task that frees up a large amount of memory when killed.
If this is set to nonzero, the OOM-killer simply kills the task that triggered the
out-of-memory condition. This avoids a possibly expensive tasklist scan.
If /proc/sys/vm/panic_on_oom is nonzero, it takes precedence over whatever value is
used in /proc/sys/vm/oom_kill_allocating_task.
The default value is 0.
/proc/sys/vm/overcommit_kbytes (since Linux 3.14)
This writable file provides an alternative to /proc/sys/vm/overcommit_ratio for
controlling the CommitLimit when /proc/sys/vm/overcommit_memory has the value 2.
It allows the amount of memory overcommitting to be specified as an absolute value
(in kB), rather than as a percentage, as is done with overcommit_ratio. This
allows for finer-grained control of CommitLimit on systems with extremely large
memory sizes.
Only one of overcommit_kbytes or overcommit_ratio can have an effect: if
overcommit_kbytes has a nonzero value, then it is used to calculate CommitLimit,
otherwise overcommit_ratio is used. Writing a value to either of these files
causes the value in the other file to be set to zero.
/proc/sys/vm/overcommit_memory
This file contains the kernel virtual memory accounting mode. Values are:
0: heuristic overcommit (this is the default)
1: always overcommit, never check
2: always check, never overcommit
In mode 0, calls of mmap(2) with MAP_NORESERVE are not checked, and the default
check is very weak, leading to the risk of getting a process "OOM-killed". Under
Linux 2.4, any nonzero value implies mode 1.
In mode 2 (available since Linux 2.6), the total virtual address space that can be
allocated (CommitLimit in /proc/meminfo) is calculated as
CommitLimit = (total_RAM - total_huge_TLB) *
overcommit_ratio / 100 + total_swap
where:
* total_RAM is the total amount of RAM on the system;
* total_huge_TLB is the amount of memory set aside for huge pages;
* overcommit_ratio is the value in /proc/sys/vm/overcommit_ratio; and
* total_swap is the amount of swap space.
For example, on a system with 16GB of physical RAM, 16GB of swap, no space
dedicated to huge pages, and an overcommit_ratio of 50, this formula yields a
CommitLimit of 24GB.
Since Linux 3.14, if the value in /proc/sys/vm/overcommit_kbytes is nonzero, then
CommitLimit is instead calculated as:
CommitLimit = overcommit_kbytes + total_swap
/proc/sys/vm/overcommit_ratio (since Linux 2.6.0)
This writable file defines a percentage by which memory can be overcommitted. The
default value in the file is 50. See the description of
/proc/sys/vm/overcommit_memory.
/proc/sys/vm/panic_on_oom (since Linux 2.6.18)
This enables or disables a kernel panic in an out-of-memory situation.
If this file is set to the value 0, the kernel's OOM-killer will kill some rogue
process. Usually, the OOM-killer is able to kill a rogue process and the system
will survive.
If this file is set to the value 1, then the kernel normally panics when out-of-
memory happens. However, if a process limits allocations to certain nodes using
memory policies (mbind(2) MPOL_BIND) or cpusets (cpuset(7)) and those nodes reach
memory exhaustion status, one process may be killed by the OOM-killer. No panic
occurs in this case: because other nodes' memory may be free, this means the system
as a whole may not have reached an out-of-memory situation yet.
If this file is set to the value 2, the kernel always panics when an out-of-memory
condition occurs.
The default value is 0. 1 and 2 are for failover of clustering. Select either
according to your policy of failover.
/proc/sys/vm/swappiness
The value in this file controls how aggressively the kernel will swap memory pages.
Higher values increase aggressiveness, lower values decrease aggressiveness. The
default value is 60.
/proc/sysrq-trigger (since Linux 2.4.21)
Writing a character to this file triggers the same SysRq function as typing ALT-
SysRq-<character> (see the description of /proc/sys/kernel/sysrq). This file is
normally writable only by root. For further details see the Linux kernel source
file Documentation/sysrq.txt.
/proc/sysvipc
Subdirectory containing the pseudo-files msg, sem and shm. These files list the
System V Interprocess Communication (IPC) objects (respectively: message queues,
semaphores, and shared memory) that currently exist on the system, providing
similar information to that available via ipcs(1). These files have headers and
are formatted (one IPC object per line) for easy understanding. svipc(7) provides
further background on the information shown by these files.
/proc/thread-self (since Linux 3.17)
This directory refers to the thread accessing the /proc filesystem, and is
identical to the /proc/self/task/[tid] directory named by the process thread ID
([tid]) of the same thread.
/proc/timer_list (since Linux 2.6.21)
This read-only file exposes a list of all currently pending (high-resolution)
timers, all clock-event sources, and their parameters in a human-readable form.
/proc/timer_stats (since Linux 2.6.21)
This is a debugging facility to make timer (ab)use in a Linux system visible to
kernel and user-space developers. It can be used by kernel and user-space
developers to verify that their code does not make undue use of timers. The goal
is to avoid unnecessary wakeups, thereby optimizing power consumption.
If enabled in the kernel (CONFIG_TIMER_STATS), but not used, it has almost zero
runtime overhead and a relatively small data-structure overhead. Even if
collection is enabled at runtime, overhead is low: all the locking is per-CPU and
lookup is hashed.
The /proc/timer_stats file is used both to control sampling facility and to read
out the sampled information.
The timer_stats functionality is inactive on bootup. A sampling period can be
started using the following command:
# echo 1 > /proc/timer_stats
The following command stops a sampling period:
# echo 0 > /proc/timer_stats
The statistics can be retrieved by:
$ cat /proc/timer_stats
While sampling is enabled, each readout from /proc/timer_stats will see newly
updated statistics. Once sampling is disabled, the sampled information is kept
until a new sample period is started. This allows multiple readouts.
Sample output from /proc/timer_stats:
$ cat /proc/timer_stats
Timer Stats Version: v0.3
Sample period: 1.764 s
Collection: active
255, 0 swapper/3 hrtimer_start_range_ns (tick_sched_timer)
71, 0 swapper/1 hrtimer_start_range_ns (tick_sched_timer)
58, 0 swapper/0 hrtimer_start_range_ns (tick_sched_timer)
4, 1694 gnome-shell mod_delayed_work_on (delayed_work_timer_fn)
17, 7 rcu_sched rcu_gp_kthread (process_timeout)
...
1, 4911 kworker/u16:0 mod_delayed_work_on (delayed_work_timer_fn)
1D, 2522 kworker/0:0 queue_delayed_work_on (delayed_work_timer_fn)
1029 total events, 583.333 events/sec
The output columns are:
* a count of the number of events, optionally (since Linux 2.6.23) followed by the
letter 'D' if this is a deferrable timer;
* the PID of the process that initialized the timer;
* the name of the process that initialized the timer;
* the function where the timer was initialized; and
* (in parentheses) the callback function that is associated with the timer.
/proc/tty
Subdirectory containing the pseudo-files and subdirectories for tty drivers and
line disciplines.
/proc/uptime
This file contains two numbers: the uptime of the system (seconds), and the amount
of time spent in idle process (seconds).
/proc/version
This string identifies the kernel version that is currently running. It includes
the contents of /proc/sys/kernel/ostype, /proc/sys/kernel/osrelease and
/proc/sys/kernel/version. For example:
Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994
/proc/vmstat (since Linux 2.6.0)
This file displays various virtual memory statistics. Each line of this file
contains a single name-value pair, delimited by white space. Some files are
present only if the kernel was configured with suitable options. (In some cases,
the options required for particular files have changed across kernel versions, so
they are not listed here. Details can be found by consulting the kernel source
code.) The following fields may be present:
nr_free_pages (since Linux 2.6.31)
nr_alloc_batch (since Linux 3.12)
nr_inactive_anon (since Linux 2.6.28)
nr_active_anon (since Linux 2.6.28)
nr_inactive_file (since Linux 2.6.28)
nr_active_file (since Linux 2.6.28)
nr_unevictable (since Linux 2.6.28)
nr_mlock (since Linux 2.6.28)
nr_anon_pages (since Linux 2.6.18)
nr_mapped (since Linux 2.6.0)
nr_file_pages (since Linux 2.6.18)
nr_dirty (since Linux 2.6.0)
nr_writeback (since Linux 2.6.0)
nr_slab_reclaimable (since Linux 2.6.19)
nr_slab_unreclaimable (since Linux 2.6.19)
nr_page_table_pages (since Linux 2.6.0)
nr_kernel_stack (since Linux 2.6.32)
Amount of memory allocated to kernel stacks.
nr_unstable (since Linux 2.6.0)
nr_bounce (since Linux 2.6.12)
nr_vmscan_write (since Linux 2.6.19)
nr_vmscan_immediate_reclaim (since Linux 3.2)
nr_writeback_temp (since Linux 2.6.26)
nr_isolated_anon (since Linux 2.6.32)
nr_isolated_file (since Linux 2.6.32)
nr_shmem (since Linux 2.6.32)
Pages used by shmem and tmpfs.
nr_dirtied (since Linux 2.6.37)
nr_written (since Linux 2.6.37)
nr_pages_scanned (since Linux 3.17)
numa_hit (since Linux 2.6.18)
numa_miss (since Linux 2.6.18)
numa_foreign (since Linux 2.6.18)
numa_interleave (since Linux 2.6.18)
numa_local (since Linux 2.6.18)
numa_other (since Linux 2.6.18)
workingset_refault (since Linux 3.15)
workingset_activate (since Linux 3.15)
workingset_nodereclaim (since Linux 3.15)
nr_anon_transparent_hugepages (since Linux 2.6.38)
nr_free_cma (since Linux 3.7)
Number of free CMA (Contiguous Memory Allocator) pages.
nr_dirty_threshold (since Linux 2.6.37)
nr_dirty_background_threshold (since Linux 2.6.37)
pgpgin (since Linux 2.6.0)
pgpgout (since Linux 2.6.0)
pswpin (since Linux 2.6.0)
pswpout (since Linux 2.6.0)
pgalloc_dma (since Linux 2.6.5)
pgalloc_dma32 (since Linux 2.6.16)
pgalloc_normal (since Linux 2.6.5)
pgalloc_high (since Linux 2.6.5)
pgalloc_movable (since Linux 2.6.23)
pgfree (since Linux 2.6.0)
pgactivate (since Linux 2.6.0)
pgdeactivate (since Linux 2.6.0)
pgfault (since Linux 2.6.0)
pgmajfault (since Linux 2.6.0)
pgrefill_dma (since Linux 2.6.5)
pgrefill_dma32 (since Linux 2.6.16)
pgrefill_normal (since Linux 2.6.5)
pgrefill_high (since Linux 2.6.5)
pgrefill_movable (since Linux 2.6.23)
pgsteal_kswapd_dma (since Linux 3.4)
pgsteal_kswapd_dma32 (since Linux 3.4)
pgsteal_kswapd_normal (since Linux 3.4)
pgsteal_kswapd_high (since Linux 3.4)
pgsteal_kswapd_movable (since Linux 3.4)
pgsteal_direct_dma
pgsteal_direct_dma32 (since Linux 3.4)
pgsteal_direct_normal (since Linux 3.4)
pgsteal_direct_high (since Linux 3.4)
pgsteal_direct_movable (since Linux 2.6.23)
pgscan_kswapd_dma
pgscan_kswapd_dma32 (since Linux 2.6.16)
pgscan_kswapd_normal (since Linux 2.6.5)
pgscan_kswapd_high
pgscan_kswapd_movable (since Linux 2.6.23)
pgscan_direct_dma
pgscan_direct_dma32 (since Linux 2.6.16)
pgscan_direct_normal
pgscan_direct_high
pgscan_direct_movable (since Linux 2.6.23)
pgscan_direct_throttle (since Linux 3.6)
zone_reclaim_failed (since linux 2.6.31)
pginodesteal (since linux 2.6.0)
slabs_scanned (since linux 2.6.5)
kswapd_inodesteal (since linux 2.6.0)
kswapd_low_wmark_hit_quickly (since 2.6.33)
kswapd_high_wmark_hit_quickly (since 2.6.33)
pageoutrun (since Linux 2.6.0)
allocstall (since Linux 2.6.0)
pgrotated (since Linux 2.6.0)
drop_pagecache (since Linux 3.15)
drop_slab (since Linux 3.15)
numa_pte_updates (since Linux 3.8)
numa_huge_pte_updates (since Linux 3.13)
numa_hint_faults (since Linux 3.8)
numa_hint_faults_local (since Linux 3.8)
numa_pages_migrated (since Linux 3.8)
pgmigrate_success (since Linux 3.8)
pgmigrate_fail (since Linux 3.8)
compact_migrate_scanned (since Linux 3.8)
compact_free_scanned (since Linux 3.8)
compact_isolated (since Linux 3.8)
compact_stall (since Linux 2.6.35)
See the kernel source file Documentation/vm/transhuge.txt.
compact_fail (since Linux 2.6.35)
See the kernel source file Documentation/vm/transhuge.txt.
compact_success (since Linux 2.6.35)
See the kernel source file Documentation/vm/transhuge.txt.
htlb_buddy_alloc_success (since Linux 2.6.26)
htlb_buddy_alloc_fail (since Linux 2.6.26)
unevictable_pgs_culled (since Linux 2.6.28)
unevictable_pgs_scanned (since Linux 2.6.28)
unevictable_pgs_rescued (since Linux 2.6.28)
unevictable_pgs_mlocked (since Linux 2.6.28)
unevictable_pgs_munlocked (since Linux 2.6.28)
unevictable_pgs_cleared (since Linux 2.6.28)
unevictable_pgs_stranded (since Linux 2.6.28)
thp_fault_alloc (since Linux 2.6.39)
See the kernel source file Documentation/vm/transhuge.txt.
thp_fault_fallback (since Linux 2.6.39)
See the kernel source file Documentation/vm/transhuge.txt.
thp_collapse_alloc (since Linux 2.6.39)
See the kernel source file Documentation/vm/transhuge.txt.
thp_collapse_alloc_failed (since Linux 2.6.39)
See the kernel source file Documentation/vm/transhuge.txt.
thp_split (since Linux 2.6.39)
See the kernel source file Documentation/vm/transhuge.txt.
thp_zero_page_alloc (since Linux 3.8)
See the kernel source file Documentation/vm/transhuge.txt.
thp_zero_page_alloc_failed (since Linux 3.8)
See the kernel source file Documentation/vm/transhuge.txt.
balloon_inflate (since Linux 3.18)
balloon_deflate (since Linux 3.18)
balloon_migrate (since Linux 3.18)
nr_tlb_remote_flush (since Linux 3.12)
nr_tlb_remote_flush_received (since Linux 3.12)
nr_tlb_local_flush_all (since Linux 3.12)
nr_tlb_local_flush_one (since Linux 3.12)
vmacache_find_calls (since Linux 3.16)
vmacache_find_hits (since Linux 3.16)
vmacache_full_flushes (since Linux 3.19)
/proc/zoneinfo (since Linux 2.6.13)
This file display information about memory zones. This is useful for analyzing
virtual memory behavior.
NOTES
Many strings (i.e., the environment and command line) are in the internal format, with
subfields terminated by null bytes ('\0'), so you may find that things are more readable
if you use od -c or tr "\000" "\n" to read them. Alternatively, echo `cat <file>` works
well.
This manual page is incomplete, possibly inaccurate, and is the kind of thing that needs
to be updated very often.
SEE ALSO
cat(1), dmesg(1), find(1), free(1), ps(1), tr(1), uptime(1), chroot(2), mmap(2),
readlink(2), syslog(2), slabinfo(5), hier(7), namespaces(7), time(7), arp(8), hdparm(8),
ifconfig(8), init(1), lsmod(8), lspci(8), mount(8), netstat(8), procinfo(8), route(8),
sysctl(8)
The Linux kernel source files: Documentation/filesystems/proc.txt
Documentation/sysctl/fs.txt, Documentation/sysctl/kernel.txt,
Documentation/sysctl/net.txt, and Documentation/sysctl/vm.txt.
COLOPHON
This page is part of release 4.04 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at http://www.kernel.org/doc/man-pages/.