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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/.