proc.5: Tweaks to Mike Frysinger's patch

[thirdparty/man-pages.git] / man5 / proc.5

.\" Copyright (C) 1994, 1995 by Daniel Quinlan (quinlan@yggdrasil.com)
.\" and Copyright (C) 2002-2008 Michael Kerrisk <mtk.manpages@gmail.com>
.\" with networking additions from Alan Cox (A.Cox@swansea.ac.uk)
.\" and scsi additions from Michael Neuffer (neuffer@mail.uni-mainz.de)
.\" and sysctl additions from Andries Brouwer (aeb@cwi.nl)
.\" and System V IPC (as well as various other) additions from
.\" Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" The GNU General Public License's references to "object code"
.\" and "executables" are to be interpreted as the output of any
.\" document formatting or typesetting system, including
.\" intermediate and printed output.
.\"
.\" This manual is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
.\" License along with this manual; if not, see
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.\" %%%LICENSE_END
.\"
.\" Modified 1995-05-17 by faith@cs.unc.edu
.\" Minor changes by aeb and Marty Leisner (leisner@sdsp.mc.xerox.com).
.\" Modified 1996-04-13, 1996-07-22 by aeb@cwi.nl
.\" Modified 2001-12-16 by rwhron@earthlink.net
.\" Modified 2002-07-13 by jbelton@shaw.ca
.\" Modified 2002-07-22, 2003-05-27, 2004-04-06, 2004-05-25
.\"    by Michael Kerrisk <mtk.manpages@gmail.com>
.\" 2004-11-17, mtk -- updated notes on /proc/loadavg
.\" 2004-12-01, mtk, rtsig-max and rtsig-nr went away in 2.6.8
.\" 2004-12-14, mtk, updated 'statm', and fixed error in order of list
.\" 2005-05-12, mtk, updated 'stat'
.\" 2005-07-13, mtk, added /proc/sys/fs/mqueue/*
.\" 2005-09-16, mtk, Added /proc/sys/fs/suid_dumpable
.\" 2005-09-19, mtk, added /proc/zoneinfo
.\" 2005-03-01, mtk, moved /proc/sys/fs/mqueue/* material to mq_overview.7.
.\" 2008-06-05, mtk, Added /proc/[pid]/oom_score, /proc/[pid]/oom_adj,
.\"     /proc/[pid]/limits, /proc/[pid]/mountinfo, /proc/[pid]/mountstats,
.\"     and /proc/[pid]/fdinfo/*.
.\" 2008-06-19, mtk, Documented /proc/[pid]/status.
.\" 2008-07-15, mtk, added /proc/config.gz
.\"
.\" FIXME 2.6.13 seems to have /proc/vmcore implemented
.\" in the source code, but there is no option available under
.\" 'make xconfig'; eventually this should be fixed, and then info
.\" from the patch-2.6.13 and change log could be used to write an
.\" entry in this man page.
.\" Needs CONFIG_VMCORE
.\"
.\" FIXME cross check against Documentation/filesystems/proc.txt
.\" to see what information could be imported from that file
.\" into this file.
.\"
.TH PROC 5 2013-06-27 "Linux" "Linux Programmer's Manual"
.SH NAME
proc \- process information pseudo-file system
.SH DESCRIPTION
The
.I proc
file system is a pseudo-file system which is used as an interface to
kernel data structures.
It is commonly mounted at
.IR /proc .
Most of it is read-only, but some files allow kernel variables to be
changed.
.LP
The following outline gives a quick tour through the
.I /proc
hierarchy.
.PD 1
.TP
.I /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.
.\" FIXME Describe /proc/[pid]/attr and
.\"       /proc/[pid]/task/[tid]/attr
.\"	  This is a directory
.\"       Added in ???
.\"	  CONFIG_SECURITY
.\"
.TP
.IR /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 \fIunsigned long\fP ID
plus one \fIunsigned long\fP value for each entry.
The last entry contains two zeros.
.TP
.IR /proc/[pid]/cgroup " (since Linux 2.6.24)"
.\" 	  Info in Documentation/cgroups/cgroups.txt
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:
.nf
.ft CW

    5:cpuacct,cpu,cpuset:/daemons
.ft
.fi
.IP
The colon-separated fields are, from left to right:
.RS 11
.IP 1. 3
hierarchy ID number
.IP 2.
set of subsystems bound to the hierarchy
.IP 3.
control group in the hierarchy to which the process belongs
.RE
.IP
This file is present only if the
.B CONFIG_CGROUPS
kernel configuration option is enabled.
.\"
.\" FIXME Describe /proc/[pid]/clear_refs
.\"       Added in 2.6.22
.\"       "Clears page referenced bits shown in smaps output"
.\"       write-only
.\"       CONFIG_PROC_PAGE_MONITOR
.TP
.I /proc/[pid]/cmdline
This holds the complete command line for the process,
unless the process is a zombie.
.\" In 2.3.26, this also used to be true if the process was swapped out.
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 (\(aq\\0\(aq),
with a further null byte after the last string.
.TP
.IR /proc/[pid]/coredump_filter " (since kernel 2.6.23)"
See
.BR core (5).
.TP
.IR /proc/[pid]/cpuset " (since kernel 2.6.12)"
.\" and/proc/[pid]/task/[tid]/cpuset
See
.BR cpuset (7).
.TP
.I /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:

.in +4n
.nf
.RB "$" " cd /proc/20/cwd; /bin/pwd"
.fi
.in

Note that the
.I pwd
command is often a shell built-in, and might
not work properly.
In
.BR bash (1),
you may use
.IR "pwd\ \-P" .

.\" The following was still true as at kernel 2.6.13
In a multithreaded process, the contents of this symbolic link
are not available if the main thread has already terminated
(typically by calling
.BR pthread_exit (3)).
.TP
.I /proc/[pid]/environ
This file contains the environment for the process.
The entries are separated by null bytes (\(aq\\0\(aq),
and there may be a null byte at the end.
Thus, to print out the environment of process 1, you would do:
.in +4n
.nf

.ft CW
.RB "$" " strings /proc/1/environ"
.fi
.ft P
.in
.TP
.I /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
.I /proc/[pid]/exe
to run another copy of the same executable as is being run by
process [pid].
.\" The following was still true as at kernel 2.6.13
In a multithreaded process, the contents of this symbolic link
are not available if the main thread has already terminated
(typically by calling
.BR pthread_exit (3)).

Under Linux 2.0 and earlier
.I /proc/[pid]/exe
is a pointer to the binary which was executed,
and appears as a symbolic link.
A
.BR 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).

.BR find (1)
with the
.I \-inum
option can be used to locate the file.
.TP
.I /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, etc.

For file descriptors for pipes and sockets,
the entries will be symbolic links whose content is the
file type with the inode.
A
.BR readlink (2)
call on this file returns a string in the format:

    type:[inode]

For example,
.I 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
.IR /proc/net/ .

.\"The following was still true as at kernel 2.6.13
In a multithreaded process, the contents of this directory
are not available if the main thread has already terminated
(typically by calling
.BR 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
.IR /proc/[pid]/fd .
For example, assuming that
.I \-i
is the flag designating an input file and
.I \-o
is the flag designating an output file:
.in +4n
.nf

.RB "$" " foobar \-i /proc/self/fd/0 \-o /proc/self/fd/1 ..."
.fi
.in

and you have a working filter.
.\" The following is not true in my tests (MTK):
.\" Note that this will not work for
.\" programs that seek on their files, as the files in the fd directory
.\" are not seekable.

.I /proc/self/fd/N
is approximately the same as
.I /dev/fd/N
in some UNIX and UNIX-like systems.
Most Linux MAKEDEV scripts symbolically link
.I /dev/fd
to
.IR /proc/self/fd ,
in fact.

Most systems provide symbolic links
.IR /dev/stdin ,
.IR /dev/stdout ,
and
.IR /dev/stderr ,
which respectively link to the files
.IR 0 ,
.IR 1 ,
and
.IR 2
in
.IR /proc/self/fd .
Thus the example command above could be written as:
.in +4n
.nf

.RB "$" " foobar \-i /dev/stdin \-o /dev/stdout ..."
.fi
.in
.\" FIXME Describe /proc/[pid]/loginuid
.\"       Added in 2.6.11; updating requires CAP_AUDIT_CONTROL
.\"       CONFIG_AUDITSYSCALL
.TP
.IR /proc/[pid]/fdinfo/ " (since kernel 2.6.22)"
This is a subdirectory containing one entry for each file which the
process has open, named by its file descriptor.
The contents of each file can be read to obtain information
about the corresponding file descriptor, for example:
.in +4n
.nf

.RB "$" " cat /proc/12015/fdinfo/4"
pos:    1000
flags:  01002002
.fi
.in

The
.I pos
field is a decimal number showing the current file offset.
The
.I flags
field is an octal number that displays the
file access mode and file status flags (see
.BR open (2)).

The files in this directory are readable only by the owner of the process.
.\" FIXME document /proc/[pid]/io
.\" .TP
.\" .IR /proc/[pid]/io " (since kernel 2.6.20)"
.TP
.IR /proc/[pid]/limits " (since kernel 2.6.24)"
This file displays the soft limit, hard limit, and units of measurement
for each of the process's resource limits (see
.BR 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,
.\" commit 3036e7b490bf7878c6dae952eec5fb87b1106589
this file is readable by all users on the system.
.TP
.IR /proc/[pid]/map_files/ " (since kernel 3.3)
.\" commit 640708a2cff7f81e246243b0073c66e6ece7e53e
This subdirectory contains entries corresponding to memory-mapped
files (see
.BR 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:
.in +4n
.nf

.RB "$" " ls -l /proc/self/map_files/"
lr\-\-\-\-\-\-\-\-. 1 root root 64 Apr 16 21:31
            3252e00000\-3252e20000 \-> /usr/lib64/ld-2.15.so
\&...
.fi
.in

Although these entries are present for memory regions that were
mapped with  the
.BR MAP_FILE
flag, the way anonymous shared memory (regions created with the
.B 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
.I /dev/zero
one:
.in +4n
.nf

.RB
lrw\-\-\-\-\-\-\-. 1 root root 64 Apr 16 21:33
            7fc075d2f000\-7fc075e6f000 \-> /dev/zero (deleted)
.fi
.in

This directory appears only if the
.B CONFIG_CHECKPOINT_RESTORE
kernel configuration option is enabled.
.TP
.I /proc/[pid]/maps
A file containing the currently mapped memory regions and their access
permissions.
See
.BR mmap (2)
for some further information about memory mappings.

The format of the file is:

.in -7n
.nf
.ft CW
.ft
.I "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]
.fi
.in

The
.I address
field is the address space in the process that the mapping occupies.
The
.I perms
field is a set of permissions:

.nf
.in +5
r = read
w = write
x = execute
s = shared
p = private (copy on write)
.fi
.in

The
.I offset
field is the offset into the file/whatever;
.I dev
is the device
(major:minor);
.I 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
.I pathname
field will usually be the file that is backing the mapping.
For ELF files,
you can easily coordinate with the
.I offset
field by looking at the
Offset field in the ELF program headers
.RI ( "readelf\ \-l" ).

There are additional helpful pseudo-paths:
.RS 12
.TP
.IR [stack]
The initial process's (also known as the main thread's) stack.
.TP
.IR [stack:<tid>] " (since Linux 3.4)"
.\" commit b76437579d1344b612cf1851ae610c636cec7db0
A thread's stack (where the
.IR <tid>
is a thread ID).
It corresponds to the
.IR /proc/[pid]/task/[tid]/
path.
.TP
.IR [vdso]
The virtual dynamically linked shared object.
.TP
.IR [heap]
The process's heap.
.in
.fi
.RE
.IP
If the
.I pathname
field is blank,
this is an anonymous mapping as obtained via the
.BR mmap (2)
function.
There is no easy way to coordinate this back to a process's source,
short of running it through
.BR gdb (1),
.BR strace (1),
or similar.

Under Linux 2.0 there is no field giving pathname.
.TP
.I /proc/[pid]/mem
This file can be used to access the pages of a process's memory through
.BR open (2),
.BR read (2),
and
.BR lseek (2).
.TP
.IR /proc/[pid]/mountinfo " (since Linux 2.6.26)"
.\" This info adapted from Documentation/filesystems/proc.txt
This file contains information about mount points.
It contains lines of the form:
.nf
.ft CW

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)
.ft
.fi
.IP
The numbers in parentheses are labels for the descriptions below:
.RS 7
.TP 5
(1)
mount ID: unique identifier of the mount (may be reused after
.BR umount (2)).
.TP
(2)
parent ID: ID of parent mount (or of self for the top of the mount tree).
.TP
(3)
major:minor: value of
.I st_dev
for files on file system (see
.BR stat (2)).
.TP
(4)
root: root of the mount within the file system.
.TP
(5)
mount point: mount point relative to the process's root.
.TP
(6)
mount options: per-mount options.
.TP
(7)
optional fields: zero or more fields of the form "tag[:value]".
.TP
(8)
separator: marks the end of the optional fields.
.TP
(9)
file system type: name of file system in the form "type[.subtype]".
.TP
(10)
mount source: file system-specific information or "none".
.TP
(11)
super options: per-super block options.
.RE
.IP
Parsers should ignore all unrecognized optional fields.
Currently the possible optional fields are:
.RS 12
.TP 18
shared:X
mount is shared in peer group X
.TP
master:X
mount is slave to peer group X
.TP
propagate_from:X
mount is slave and receives propagation from peer group X (*)
.TP
unbindable
mount is unbindable
.RE
.IP
(*) 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:
.I Documentation/filesystems/sharedsubtree.txt
in the Linux kernel source tree.
.TP
.IR /proc/[pid]/mounts " (since Linux 2.4.19)"
This is a list of all the file systems currently mounted in the
process's mount namespace.
The format of this file is documented in
.BR 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 file system mount or unmount) causes
.BR select (2)
to mark the file descriptor as readable, and
.BR poll (2)
and
.BR epoll_wait (2)
mark the file as having an error condition.
.TP
.IR /proc/[pid]/mountstats " (since Linux 2.6.17)"
This file exports information (statistics, configuration information)
about the mount points in the process's name space.
Lines in this file have the form:
.nf

device /dev/sda7 mounted on /home with fstype ext3 [statistics]
(       1      )            ( 2 )             (3 ) (4)
.fi
.IP
The fields in each line are:
.RS 7
.TP 5
(1)
The name of the mounted device
(or "nodevice" if there is no corresponding device).
.TP
(2)
The mount point within the file system tree.
.TP
(3)
The file system type.
.TP
(4)
Optional statistics and configuration information.
Currently (as at Linux 2.6.26), only NFS file systems export
information via this field.
.RE
.IP
This file is readable only by the owner of the process.
.TP
.IR /proc/[pid]/ns/ " (since Linux 3.0)"
.\" See commit 6b4e306aa3dc94a0545eb9279475b1ab6209a31f
This is a subdirectory containing one entry for each namespace that
supports being manipulated by
.BR setns (2).
For information about namespaces, see
.BR clone (2).
.TP
.IR /proc/[pid]/ns/ipc " (since Linux 3.0)"
Bind mounting this file (see
.BR mount (2))
to somewhere else in the filesystem keeps
the IPC namespace of the process specified by
.I pid
alive even if all processes currently in the namespace terminate.

Opening this file returns a file handle for the IPC namespace
of the process specified by
.IR pid .
As long as this file descriptor remains open,
the IPC namespace will remain alive,
even if all processes in the namespace terminate.
The file descriptor can be passed to
.BR setns (2).
.TP
.IR /proc/[pid]/ns/net " (since Linux 3.0)"
Bind mounting this file (see
.BR mount (2))
to somewhere else in the filesystem keeps
the network namespace of the process specified by
.I pid
alive even if all processes in the namespace terminate.

Opening this file returns a file handle for the network namespace
of the process specified by
.IR pid .
As long as this file descriptor remains open,
the network namespace will remain alive,
even if all processes in the namespace terminate.
The file descriptor can be passed to
.BR setns (2).
.TP
.IR /proc/[pid]/ns/uts " (since Linux 3.0)"
Bind mounting this file (see
.BR mount (2))
to somewhere else in the filesystem keeps
the UTS namespace of the process specified by
.I pid
alive even if all processes currently in the namespace terminate.

Opening this file returns a file handle for the UTS namespace
of the process specified by
.IR pid .
As long as this file descriptor remains open,
the UTS namespace will remain alive,
even if all processes in the namespace terminate.
The file descriptor can be passed to
.BR setns (2).
.TP
.IR /proc/[pid]/numa_maps " (since Linux 2.6.14)"
See
.BR numa (7).
.TP
.IR /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
.IR 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.
.IP
The default value for this file is 0;
a new process inherits its parent's
.I oom_adj
setting.
A process must be privileged
.RB ( CAP_SYS_RESOURCE )
to update this file.
.IP
Since Linux 2.6.36, use of this file is deprecated in favor of
.IR /proc/[pid]/oom_score_adj .
.TP
.IR /proc/[pid]/oom_score " (since Linux 2.6.11)"
.\" See mm/oom_kill.c::badness() in the 2.6.25 sources
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:
.\" See mm/oom_kill.c::badness() in the 2.6.25 sources
.RS
.IP * 2
whether the process creates a lot of children using
.BR fork (2)
(+);
.IP *
whether the process has been running a long time,
or has used a lot of CPU time (\-);
.IP *
whether the process has a low nice value (i.e., > 0) (+);
.IP *
whether the process is privileged (\-); and
.\" More precisely, if it has CAP_SYS_ADMIN or CAP_SYS_RESOURCE
.IP *
whether the process is making direct hardware access (\-).
.\" More precisely, if it has CAP_SYS_RAWIO
.RE
.IP
The
.I oom_score
also reflects the adjustment specified by the
.I oom_score_adj
or
.I oom_adj
setting for the process.
.TP
.IR /proc/[pid]/oom_score_adj " (since Linux 2.6.36)"
.\" Text taken from 3.7 Documentation/filesystems/proc.txt
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
.BR 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
.I 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
.I 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,
.I /proc/[pid]/oom_adj
can still be used to tune the badness score.
Its value is
scaled linearly with
.IR oom_score_adj .

Writing to
.IR /proc/[pid]/oom_score_adj
or
.IR /proc/[pid]/oom_adj
will change the other with its scaled value.
.\" FIXME Describe /proc/[pid]/pagemap
.\"       Added in 2.6.25
.\"       CONFIG_PROC_PAGE_MONITOR
.TP
.I /proc/[pid]/root
UNIX and Linux support the idea of a per-process root of the
file system, set by the
.BR chroot (2)
system call.
This file is a symbolic link that points to the process's
root directory, and behaves as exe, fd/*, etc. do.

.\" The following was still true as at kernel 2.6.13
In a multithreaded process, the contents of this symbolic link
are not available if the main thread has already terminated
(typically by calling
.BR pthread_exit (3)).
.\" FIXME Describe /proc/[pid]/seccomp
.\"       Added in 2.6.12
.\" FIXME Describe /proc/[pid]/sessionid
.\"       Added in 2.6.25; read-only; only readable by real UID
.\"       CONFIG_AUDITSYSCALL
.\" FIXME Describe /proc/[pid]/sched
.\"       Added in 2.6.23
.\"       CONFIG_SCHED_DEBUG, and additional fields if CONFIG_SCHEDSTATS
.\"       Displays various scheduling parameters
.\"       This file can be written, to reset stats
.\" FIXME Describe /proc/[pid]/schedstats and
.\"       /proc/[pid]/task/[tid]/schedstats
.\"       Added in 2.6.9
.\"       CONFIG_SCHEDSTATS
.TP
.IR /proc/[pid]/smaps " (since Linux 2.6.14)"
.\"       CONFIG_PROC_PAGE_MONITOR
This file shows memory consumption for each of the process's mappings.
For each of mappings there is a series of lines such as the following:
.in +4n
.nf

08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
Size:               464 kB
Rss:                424 kB
Shared_Clean:       424 kB
Shared_Dirty:         0 kB
Private_Clean:        0 kB
Private_Dirty:        0 kB

.fi
.in
The first of these lines shows the same information as is displayed
for the mapping in
.IR /proc/[pid]/maps .
The remaining lines show the size of the mapping,
the amount of the mapping that is currently resident in RAM,
the number of clean and dirty shared pages in the mapping,
and the number of clean and dirty private pages in the mapping.

This file is present only if the
.B CONFIG_MMU
kernel configuration
option is enabled.
.TP
.I /proc/[pid]/stat
Status information about the process.
This is used by
.BR ps (1).
It is defined in
.IR /usr/src/linux/fs/proc/array.c "."

The fields, in order, with their proper
.BR scanf (3)
format specifiers, are:
.RS
.TP 12
\fIpid\fP %d
(1) The process ID.
.TP
\fIcomm\fP %s
(2) The filename of the executable, in parentheses.
This is visible whether or not the executable is swapped out.
.TP
\fIstate\fP %c
(3) One character from the string "RSDZTW" where R is running, S is
sleeping in an interruptible wait, D is waiting in uninterruptible
disk sleep, Z is zombie, T is traced or stopped (on a signal),
and W is paging.
.TP
\fIppid\fP %d
(4) The PID of the parent.
.TP
\fIpgrp\fP %d
(5) The process group ID of the process.
.TP
\fIsession\fP %d
(6) The session ID of the process.
.TP
\fItty_nr\fP %d
(7) 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.)
.TP
\fItpgid\fP %d
.\" This field and following, up to and including wchan added 0.99.1
(8) The ID of the foreground process group of the controlling
terminal of the process.
.TP
\fIflags\fP %u (%lu before Linux 2.6.22)
(9) The kernel flags word of the process.
For bit meanings,
see the PF_* defines in the Linux kernel source file
.IR include/linux/sched.h .
Details depend on the kernel version.
.TP
\fIminflt\fP %lu
(10) The number of minor faults the process has made which have not
required loading a memory page from disk.
.TP
\fIcminflt\fP %lu
(11) The number of minor faults that the process's
waited-for children have made.
.TP
\fImajflt\fP %lu
(12) The number of major faults the process has made which have
required loading a memory page from disk.
.TP
\fIcmajflt\fP %lu
(13) The number of major faults that the process's
waited-for children have made.
.TP
\fIutime\fP %lu
(14) Amount of time that this process has been scheduled in user mode,
measured in clock ticks (divide by
.IR sysconf(_SC_CLK_TCK) ).
This includes guest time, \fIguest_time\fP
(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.
.TP
\fIstime\fP %lu
(15) Amount of time that this process has been scheduled in kernel mode,
measured in clock ticks (divide by
.IR sysconf(_SC_CLK_TCK) ).
.TP
\fIcutime\fP %ld
(16) Amount of time that this process's
waited-for children have been scheduled in user mode,
measured in clock ticks (divide by
.IR sysconf(_SC_CLK_TCK) ).
(See also
.BR times (2).)
This includes guest time, \fIcguest_time\fP
(time spent running a virtual CPU, see below).
.TP
\fIcstime\fP %ld
(17) Amount of time that this process's
waited-for children have been scheduled in kernel mode,
measured in clock ticks (divide by
.IR sysconf(_SC_CLK_TCK) ).
.TP
\fIpriority\fP %ld
(18) (Explanation for Linux 2.6)
For processes running a real-time scheduling policy
.RI ( policy
below; see
.BR 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
.RB ( 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.
.\" And back in kernel 1.2 days things were different again.
.TP
\fInice\fP %ld
(19) The nice value (see
.BR setpriority (2)),
a value in the range 19 (low priority) to \-20 (high priority).
.\" Back in kernel 1.2 days things were different.
.\" .TP
.\" \fIcounter\fP %ld
.\" The current maximum size in jiffies of the process's next timeslice,
.\" or what is currently left of its current timeslice, if it is the
.\" currently running process.
.\" .TP
.\" \fItimeout\fP %u
.\" The time in jiffies of the process's next timeout.
.\" timeout was removed sometime around 2.1/2.2
.TP
\fInum_threads\fP %ld
(20) 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.
.TP
\fIitrealvalue\fP %ld
(21) The time in jiffies before the next
.B 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.
.TP
\fIstarttime\fP %llu (was %lu before Linux 2.6)
(22) 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
.IR sysconf(_SC_CLK_TCK) ).
.TP
\fIvsize\fP %lu
(23) Virtual memory size in bytes.
.TP
\fIrss\fP %ld
(24) 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.
.TP
\fIrsslim\fP %lu
(25) Current soft limit in bytes on the rss of the process;
see the description of
.B RLIMIT_RSS
in
.BR getrlimit (2).
.TP
\fIstartcode\fP %lu
(26) The address above which program text can run.
.TP
\fIendcode\fP %lu
(27) The address below which program text can run.
.TP
\fIstartstack\fP %lu
(28) The address of the start (i.e., bottom) of the stack.
.TP
\fIkstkesp\fP %lu
(29) The current value of ESP (stack pointer), as found in the
kernel stack page for the process.
.TP
\fIkstkeip\fP %lu
(30) The current EIP (instruction pointer).
.TP
\fIsignal\fP %lu
(31) The bitmap of pending signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals; use
.I /proc/[pid]/status
instead.
.TP
\fIblocked\fP %lu
(32) The bitmap of blocked signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals; use
.I /proc/[pid]/status
instead.
.TP
\fIsigignore\fP %lu
(33) The bitmap of ignored signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals; use
.I /proc/[pid]/status
instead.
.TP
\fIsigcatch\fP %lu
(34) The bitmap of caught signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals; use
.I /proc/[pid]/status
instead.
.TP
\fIwchan\fP %lu
(35) This is the "channel" in which the process is waiting.
It is the
address of a system call, and can be looked up in a namelist if you
need a textual name.
(If you have an up-to-date
.IR /etc/psdatabase ,
then
try \fIps \-l\fP to see the WCHAN field in action.)
.TP
\fInswap\fP %lu
(36)
.\" nswap was added in 2.0
Number of pages swapped (not maintained).
.TP
\fIcnswap\fP %lu
(37)
.\" cnswap was added in 2.0
Cumulative \fInswap\fP for child processes (not maintained).
.TP
\fIexit_signal\fP %d (since Linux 2.1.22)
(38) Signal to be sent to parent when we die.
.TP
\fIprocessor\fP %d (since Linux 2.2.8)
(39) CPU number last executed on.
.TP
\fIrt_priority\fP %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
(40) 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
.BR sched_setscheduler (2)).
.TP
\fIpolicy\fP %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
(41) Scheduling policy (see
.BR sched_setscheduler (2)).
Decode using the SCHED_* constants in
.IR linux/sched.h .
.TP
\fIdelayacct_blkio_ticks\fP %llu (since Linux 2.6.18)
(42) Aggregated block I/O delays, measured in clock ticks (centiseconds).
.TP
\fIguest_time\fP %lu (since Linux 2.6.24)
(43) Guest time of the process (time spent running a virtual CPU
for a guest operating system), measured in clock ticks (divide by
.IR sysconf(_SC_CLK_TCK) ).
.TP
\fIcguest_time\fP %ld (since Linux 2.6.24)
(44) Guest time of the process's children, measured in clock ticks (divide by
.IR sysconf(_SC_CLK_TCK) ).
.RE
.TP
.I /proc/[pid]/statm
Provides information about memory usage, measured in pages.
The columns are:
.in +4n
.nf

size       (1) total program size
           (same as VmSize in \fI/proc/[pid]/status\fP)
resident   (2) resident set size
           (same as VmRSS in \fI/proc/[pid]/status\fP)
share      (3) shared pages (i.e., backed by a file)
text       (4) text (code)
.\" (not including libs; broken, includes data segment)
lib        (5) library (unused in Linux 2.6)
data       (6) data + stack
.\" (including libs; broken, includes library text)
dt         (7) dirty pages (unused in Linux 2.6)
.fi
.in
.TP
.I /proc/[pid]/status
Provides much of the information in
.I /proc/[pid]/stat
and
.I /proc/[pid]/statm
in a format that's easier for humans to parse.
Here's an example:
.in +4n
.nf

.RB "$" " 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
VmHWM:      7572 kB
VmRSS:      6316 kB
VmData:     5224 kB
VmStk:        88 kB
VmExe:       572 kB
VmLib:      1708 kB
VmPTE:        20 kB
Threads:        1
SigQ:   0/3067
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000010000
SigIgn: 0000000000384004
SigCgt: 000000004b813efb
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
Cpus_allowed:   00000001
Cpus_allowed_list:      0
Mems_allowed:   1
Mems_allowed_list:      0
voluntary_ctxt_switches:        150
nonvoluntary_ctxt_switches:     545
.fi
.in
.IP
The fields are as follows:
.RS
.IP * 2
.IR Name :
Command run by this process.
.IP *
.IR 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)".
.IP *
.IR Tgid :
Thread group ID (i.e., Process ID).
.IP *
.IR Pid :
Thread ID (see
.BR gettid (2)).
.IP *
.IR PPid :
PID of parent process.
.IP *
.IR TracerPid :
PID of process tracing this process (0 if not being traced).
.IP *
.IR Uid ", " Gid :
Real, effective, saved set, and file system UIDs (GIDs).
.IP *
.IR FDSize :
Number of file descriptor slots currently allocated.
.IP *
.IR Groups :
Supplementary group list.
.IP *
.IR VmPeak :
Peak virtual memory size.
.IP *
.IR VmSize :
Virtual memory size.
.IP *
.IR VmLck :
Locked memory size (see
.BR mlock (3)).
.IP *
.IR VmHWM :
Peak resident set size ("high water mark").
.IP *
.IR VmRSS :
Resident set size.
.IP *
.IR VmData ", " VmStk ", " VmExe :
Size of data, stack, and text segments.
.IP *
.IR VmLib :
Shared library code size.
.IP *
.IR VmPTE :
Page table entries size (since Linux 2.6.10).
.IP *
.IR Threads :
Number of threads in process containing this thread.
.IP *
.IR 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
.BR RLIMIT_SIGPENDING
in
.BR getrlimit (2)).
.IP *
.IR SigPnd ", " ShdPnd :
Number of signals pending for thread and for process as a whole (see
.BR pthreads (7)
and
.BR signal (7)).
.IP *
.IR SigBlk ", " SigIgn ", " SigCgt :
Masks indicating signals being blocked, ignored, and caught (see
.BR signal (7)).
.IP *
.IR CapInh ", " CapPrm ", " CapEff :
Masks of capabilities enabled in inheritable, permitted, and effective sets
(see
.BR capabilities (7)).
.IP *
.IR CapBnd :
Capability Bounding set
(since kernel 2.6.26, see
.BR capabilities (7)).
.IP *
.IR Cpus_allowed :
Mask of CPUs on which this process may run
(since Linux 2.6.24, see
.BR cpuset (7)).
.IP *
.IR Cpus_allowed_list :
Same as previous, but in "list format"
(since Linux 2.6.26, see
.BR cpuset (7)).
.IP *
.IR Mems_allowed :
Mask of memory nodes allowed to this process
(since Linux 2.6.24, see
.BR cpuset (7)).
.IP *
.IR Mems_allowed_list :
Same as previous, but in "list format"
(since Linux 2.6.26, see
.BR cpuset (7)).
.IP *
.IR voluntary_context_switches ", " nonvoluntary_context_switches :
Number of voluntary and involuntary context switches (since Linux 2.6.23).
.RE
.TP
.IR /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
.RI ( [tid] )
of the thread (see
.BR gettid (2)).
Within each of these subdirectories, there is a set of
files with the same names and contents as under the
.I /proc/[pid]
directories.
For attributes that are shared by all threads, the contents for
each of the files under the
.I task/[tid]
subdirectories will be the same as in the corresponding
file in the parent
.I /proc/[pid]
directory
(e.g., in a multithreaded process, all of the
.I task/[tid]/cwd
files will have the same value as the
.I /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
.I task/[tid]
may have different values (e.g., various fields in each of the
.I task/[tid]/status
files may be different for each thread).

.\" The following was still true as at kernel 2.6.13
In a multithreaded process, the contents of the
.I /proc/[pid]/task
directory are not available if the main thread has already terminated
(typically by calling
.BR pthread_exit (3)).
.TP
.I /proc/apm
Advanced power management version and battery information when
.B CONFIG_APM
is defined at kernel compilation time.
.TP
.I /proc/bus
Contains subdirectories for installed busses.
.TP
.I /proc/bus/pccard
Subdirectory for PCMCIA devices when
.B CONFIG_PCMCIA
is set at kernel compilation time.
.TP
.I /proc/bus/pccard/drivers
.TP
.I /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.
.TP
.I /proc/bus/pci/devices
Information about PCI devices.
They may be accessed through
.BR lspci (8)
and
.BR setpci (8).
.TP
.I /proc/cmdline
Arguments passed to the Linux kernel at boot time.
Often done via a boot manager such as
.BR lilo (8)
or
.BR grub (8).
.TP
.IR /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
.I .config
file that resulted when configuring the kernel (using
.IR "make xconfig" ,
.IR "make config" ,
or similar).
The file contents are compressed; view or search them using
.BR zcat (1),
.BR zgrep (1),
etc.
As long as no changes have been made to the following file,
the contents of
.I /proc/config.gz
are the same as those provided by :
.in +4n
.nf

cat /lib/modules/$(uname \-r)/build/.config
.fi
.in
.IP
.I /proc/config.gz
is provided only if the kernel is configured with
.BR CONFIG_IKCONFIG_PROC .
.TP
.I /proc/cpuinfo
This is a collection of CPU and system architecture dependent items,
for each supported architecture a different list.
Two common entries are \fIprocessor\fP which gives CPU number and
\fIbogomips\fP; a system constant that is calculated
during kernel initialization.
SMP machines have information for
each CPU.
The
.BR lscpu (1)
command gathers its information from this file.
.TP
.I /proc/devices
Text listing of major numbers and device groups.
This can be used by MAKEDEV scripts for consistency with the kernel.
.TP
.IR /proc/diskstats " (since Linux 2.5.69)"
This file contains disk I/O statistics for each disk device.
See the Linux kernel source file
.I Documentation/iostats.txt
for further information.
.TP
.I /proc/dma
This is a list of the registered \fIISA\fP DMA (direct memory access)
channels in use.
.TP
.I /proc/driver
Empty subdirectory.
.TP
.I /proc/execdomains
List of the execution domains (ABI personalities).
.TP
.I /proc/fb
Frame buffer information when
.B CONFIG_FB
is defined during kernel compilation.
.TP
.I /proc/filesystems
A text listing of the file systems which are supported by the kernel,
namely file systems which were compiled into the kernel or whose kernel
modules are currently loaded.
(See also
.BR filesystems (5).)
If a file system is marked with "nodev",
this means that it does not require a block device to be mounted
(e.g., virtual file system, network file system).

Incidentally, this file may be used by
.BR mount (8)
when no file system is specified and it didn't manage to determine the
file system type.
Then file systems contained in this file are tried
(excepted those that are marked with "nodev").
.TP
.I /proc/fs
Empty subdirectory.
.TP
.I /proc/ide
This directory
exists on systems with the IDE bus.
There are directories for each IDE channel and attached device.
Files include:

.in +4n
.nf
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
.fi
.in

The
.BR hdparm (8)
utility provides access to this information in a friendly format.
.TP
.I /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.
.TP
.I /proc/iomem
I/O memory map in Linux 2.4.
.TP
.I /proc/ioports
This is a list of currently registered Input-Output port regions that
are in use.
.TP
.IR /proc/kallsyms " (since Linux 2.5.71)"
This holds the kernel exported symbol definitions used by the
.BR 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
.IR ksyms .
.TP
.I /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
.RI ( /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.
.TP
.I /proc/kmsg
This file can be used instead of the
.BR 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
.BR syslog (2)
system call facility to log kernel messages.

Information in this file is retrieved with the
.BR dmesg (1)
program.
.TP
.IR /proc/ksyms " (Linux 1.1.23-2.5.47)"
See
.IR /proc/kallsyms .
.TP
.I /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
.BR 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.
.TP
.I /proc/locks
This file shows current file locks
.RB ( flock "(2) and " fcntl (2))
and leases
.RB ( fcntl (2)).
.TP
.IR /proc/malloc " (only up to and including Linux 2.2)"
.\" It looks like this only ever did something back in 1.0 days
This file is present only if
.B CONFIG_DEBUG_MALLOC
was defined during compilation.
.TP
.I /proc/meminfo
This file reports statistics about memory usage on the system.
It is used by
.BR 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 fileds are displayed only if the kernel was configured
with various options; those dependencies are noted in the list.
.RS
.TP
.IR MemTotal " %lu"
Total usable RAM (i.e. physical RAM minus a few reserved
bits and the kernel binary code).
.TP
.IR MemFree " %lu"
The sum of
.IR LowFree + HighFree .
.TP
.IR Buffers " %lu"
Relatively temporary storage for raw disk blocks that
shouldn't get tremendously large (20MB or so).
.TP
.IR Cached " %lu"
In-memory cache for files read from the disk (the page cache).
Doesn't include
.IR SwapCached .
.TP
.IR 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.)
.TP
.IR Active " %lu"
Memory that has been used more recently and usually not
reclaimed unless absolutely necessary.
.TP
.IR Inactive " %lu"
Memory which has been less recently used.
It is more eligible to be reclaimed for other purposes.
.TP
.IR Active(anon) " %lu (since Linux 2.6.28)"
[To be documented.]
.TP
.IR Inactive(anon) " %lu (since Linux 2.6.28)"
[To be documented.]
.TP
.IR Active(file) " %lu (since Linux 2.6.28)"
[To be documented.]
.TP
.IR Inactive(file) " %lu (since Linux 2.6.28)"
[To be documented.]
.TP
.IR Unevictable " %lu (since Linux 2.6.28)"
(From Linux 2.6.28 to 2.6.30,
\fBCONFIG_UNEVICTABLE_LRU\fP was required.)
[To be documented.]
.TP
.IR Mlocked " %lu (since Linux 2.6.28)"
(From Linux 2.6.28 to 2.6.30,
\fBCONFIG_UNEVICTABLE_LRU\fP was required.)
[To be documented.]
.TP
.IR HighTotal " %lu"
(Starting with Linux 2.6.19, \fBCONFIG_HIGHMEM\fP 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.
.TP
.IR HighFree " %lu
(Starting with Linux 2.6.19, \fBCONFIG_HIGHMEM\fP is required.)
Amount of free highmem.
.TP
.IR LowTotal " %lu
(Starting with Linux 2.6.19, \fBCONFIG_HIGHMEM\fP 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
.I Slab
is allocated.
Bad things happen when you're out of lowmem.
.TP
.IR LowFree " %lu
(Starting with Linux 2.6.19, \fBCONFIG_HIGHMEM\fP is required.)
Amount of free lowmem.
.TP
.IR MmapCopy " %lu (since Linux 2.6.29)"
.RB ( CONFIG_MMU
is required.)
[To be documented.]
.TP
.IR SwapTotal " %lu"
Total amount of swap space available.
.TP
.IR SwapFree " %lu"
Amount of swap space that is currently unused.
.TP
.IR Dirty " %lu"
Memory which is waiting to get written back to the disk.
.TP
.IR Writeback " %lu"
Memory which is actively being written back to the disk.
.TP
.IR AnonPages " %lu (since Linux 2.6.18)"
Non-file backed pages mapped into user-space page tables.
.TP
.IR Mapped " %lu"
Files which have been mmaped, such as libraries.
.TP
.IR Shmem " %lu (since Linux 2.6.32)"
[To be documented.]
.TP
.IR Slab " %lu"
In-kernel data structures cache.
.TP
.IR SReclaimable " %lu (since Linux 2.6.19)"
Part of
.IR Slab ,
that might be reclaimed, such as caches.
.TP
.IR SUnreclaim " %lu (since Linux 2.6.19)"
Part of
.IR Slab ,
that cannot be reclaimed on memory pressure.
.TP
.IR KernelStack " %lu (since Linux 2.6.32)"
Amount of memory allocated to kernel stacks.
.TP
.IR PageTables " %lu (since Linux 2.6.18)"
Amount of memory dedicated to the lowest level of page tables.
.TP
.IR Quicklists " %lu (since Linux 2.6.27)"
(\fBCONFIG_QUICKLIST\fP is required.)
[To be documented.]
.TP
.IR NFS_Unstable " %lu (since Linux 2.6.18)"
NFS pages sent to the server, but not yet committed to stable storage.
.TP
.IR Bounce " %lu (since Linux 2.6.18)"
Memory used for block device "bounce buffers".
.TP
.IR WritebackTmp " %lu (since Linux 2.6.26)"
Memory used by FUSE for temporary writeback buffers.
.TP
.IR CommitLimit " %lu (since Linux 2.6.10)"
Based on the overcommit ratio ('vm.overcommit_ratio'),
this is the total amount of  memory currently available to
be allocated on the system.
This limit is adhered to
only if strict overcommit accounting is enabled (mode 2 in
.IR /proc/sys/vm/overcommit_ratio ).
The
.I CommitLimit
is calculated using the following formula:

    CommitLimit = (overcommit_ratio * Physical RAM) + Swap

For example, on a system with 1GB of physical RAM and 7GB
of swap with a
.I overcommit_ratio
of 30, this formula yields a
.I CommitLimit
of 7.3GB.
For more details, see the memory overcommit documentation
in the kernel source file
.IR Documentation/vm/overcommit-accounting .
.TP
.IR 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
.BR 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
.IR /proc/sys/vm/overcommit_memory ),
allocations which would exceed the
.I CommitLimit
(detailed above) 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.
.TP
.IR VmallocTotal " %lu"
Total size of vmalloc memory area.
.TP
.IR VmallocUsed " %lu"
Amount of vmalloc area which is used.
.TP
.IR VmallocChunk " %lu"
Largest contiguous block of vmalloc area which is free.
.TP
.IR HardwareCorrupted " %lu (since Linux 2.6.32)"
(\fBCONFIG_MEMORY_FAILURE\fP is required.)
[To be documented.]
.TP
.IR AnonHugePages " %lu (since Linux 2.6.38)"
(\fBCONFIG_TRANSPARENT_HUGEPAGE\fP is required.)
Non-file backed huge pages mapped into user-space page tables.
.TP
.IR HugePages_Total " %lu"
(\fBCONFIG_HUGETLB_PAGE\fP is required.)
The size of the pool of huge pages.
.TP
.IR HugePages_Free " %lu"
(\fBCONFIG_HUGETLB_PAGE\fP is required.)
The number of huge pages in the pool that are not yet allocated.
.TP
.IR HugePages_Rsvd " %lu (since Linux 2.6.17)"
(\fBCONFIG_HUGETLB_PAGE\fP 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.
.TP
.IR HugePages_Surp " %lu (since Linux 2.6.24)"
(\fBCONFIG_HUGETLB_PAGE\fP is required.)
This is the number of huge pages in
the pool above the value in
.IR /proc/sys/vm/nr_hugepages .
The maximum number of surplus huge pages is controlled by
.IR /proc/sys/vm/nr_overcommit_hugepages .
.TP
.IR Hugepagesize " %lu"
(\fBCONFIG_HUGETLB_PAGE\fP is required.)
The size of huge pages.
.RE
.TP
.I /proc/modules
A text list of the modules that have been loaded by the system.
See also
.BR lsmod (8).
.TP
.I /proc/mounts
Before kernel 2.4.19, this file was a list
of all the file systems currently mounted on the system.
With the introduction of per-process mount namespaces in
Linux 2.4.19, this file became a link to
.IR /proc/self/mounts ,
which lists the mount points of the process's own mount namespace.
The format of this file is documented in
.BR fstab (5).
.TP
.I /proc/mtrr
Memory Type Range Registers.
See the Linux kernel source file
.I Documentation/mtrr.txt
for details.
.TP
.I /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
.BR cat (1).
However, the standard
.BR netstat (8)
suite provides much cleaner access to these files.
.TP
.I /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:

.nf
.ft CW
.in 8n
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
.ft
.fi
.in

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
.IR /usr/include/linux/if_arp.h )
and
the "HW address" is the data link layer mapping for that IP address if
it is known.
.TP
.I /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
.BR ifconfig (8)
program to report device status.
The format is:

.nf
.ft CW
.in 1n
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
.in
.ft
.fi
.\" .TP
.\" .I /proc/net/ipx
.\" No information.
.\" .TP
.\" .I /proc/net/ipx_route
.\" No information.
.TP
.I /proc/net/dev_mcast
Defined in
.IR /usr/src/linux/net/core/dev_mcast.c :
.nf
.in +5
indx interface_name  dmi_u dmi_g dmi_address
2    eth0            1     0     01005e000001
3    eth1            1     0     01005e000001
4    eth2            1     0     01005e000001
.in
.fi
.TP
.I /proc/net/igmp
Internet Group Management Protocol.
Defined in
.IR /usr/src/linux/net/core/igmp.c .
.TP
.I /proc/net/rarp
This file uses the same format as the
.I arp
file and contains the current reverse mapping database used to provide
.BR rarp (8)
reverse address lookup services.
If RARP is not configured into the
kernel,
this file will not be present.
.TP
.I /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.
.\" .TP
.\" .I /proc/net/route
.\" No information, but looks similar to
.\" .BR route (8).
.TP
.I /proc/net/snmp
This file holds the ASCII data needed for the IP, ICMP, TCP, and UDP
management
information bases for an SNMP agent.
.TP
.I /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 only useful for debugging.
The "uid"
field holds the effective UID of the creator of the socket.
.TP
.I /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:

.nf
.ft CW
.in 1n
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
.in
.ft
.fi
.TP
.I /proc/net/unix
Lists the UNIX domain sockets present within the system and their
status.
The format is:
.nf
.sp .5
.ft CW
Num RefCount Protocol Flags    Type St Path
 0: 00000002 00000000 00000000 0001 03
 1: 00000001 00000000 00010000 0001 01 /dev/printer
.ft
.sp .5
.fi

Here "Num" is the kernel table slot number, "RefCount" is the number
of users of the socket, "Protocol" is currently always 0, "Flags"
represent the internal kernel flags holding the status of the
socket.
Currently, type is always "1" (UNIX domain datagram sockets are
not yet supported in the kernel).
\&"St" is the internal state of the
socket and Path is the bound path (if any) of the socket.
.TP
.I /proc/partitions
Contains major and minor numbers of each partition as well as number
of blocks and partition name.
.TP
.I /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
.I /proc
interface for PCI
.RI ( /proc/bus/pci ).
It became optional in Linux 2.2 (available with
.B 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
.B CONFIG_PCI_LEGACY_PROC
set), and finally removed altogether since Linux 2.6.17.
.\" FIXME /proc/sched_debug
.\" .TP
.\" .IR /proc/sched_debug " (since Linux 2.6.23)"
.\" See also /proc/[pid]/sched
.TP
.IR /proc/profile " (since Linux 2.4)"
This file is present only if the kernel was booted with the
.I profile=1
command-line option.
It exposes kernel profiling information in a binary format for use by
.BR 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
.IR sizeof(int)
sets the profiling interrupt frequency.
.TP
.I /proc/scsi
A directory with the
.I 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
.BR cat (1).

You can also write to some of the files to reconfigure the subsystem or
switch certain features on or off.
.TP
.I /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 \fIadd-single-device\fP command which
allows root to add a hotplugged device to the list of known devices.

The command
.in +4n
.nf

echo \(aqscsi add-single-device 1 0 5 0\(aq > /proc/scsi/scsi

.fi
.in
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.
.TP
.I /proc/scsi/[drivername]
\fI[drivername]\fP 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, etc.

Writing to these files allows different things on different hosts.
For example, with the \fIlatency\fP and \fInolatency\fP commands,
root can switch on and off command latency measurement code in the
eata_dma driver.
With the \fIlockup\fP and \fIunlock\fP commands,
root can control bus lockups simulated by the scsi_debug driver.
.TP
.I /proc/self
This directory refers to the process accessing the
.I /proc
file system,
and is identical to the
.I /proc
directory named by the process ID of the same process.
.TP
.I /proc/slabinfo
Information about kernel caches.
Since Linux 2.6.16 this file is present only if the
.B CONFIG_SLAB
kernel configuration option is enabled.
The columns in
.I /proc/slabinfo
are:
.in +4n
.nf

cache-name
num-active-objs
total-objs
object-size
num-active-slabs
total-slabs
num-pages-per-slab
.fi
.in

See
.BR slabinfo (5)
for details.
.TP
.I /proc/stat
kernel/system statistics.
Varies with architecture.
Common
entries include:
.RS
.TP
\fIcpu  3357 0 4313 1362393\fP
The amount of time, measured in units of
USER_HZ (1/100ths of a second on most architectures, use
.IR sysconf(_SC_CLK_TCK)
to obtain the right value),
.\" 1024 on Alpha and ia64
that the system spent in various states:
.RS
.TP
.I user
(1) Time spent in user mode.
.TP
.I nice
(2) Time spent in user mode with low priority (nice).
.TP
.I system
(3) Time spent in system mode.
.TP
.I idle
(4) Time spent in the idle task.
.\" FIXME Actually, the following info about the /proc/stat 'cpu' field
.\"       does not seem to be quite right (at least in 2.6.12 or 3.6):
.\"       the idle time in /proc/uptime does not quite match this value
This value should be USER_HZ times the
second entry in the
.I /proc/uptime
pseudo-file.
.TP
.IR iowait " (since Linux 2.5.41)"
(5) Time waiting for I/O to complete.
.TP
.IR irq " (since Linux 2.6.0-test4)"
(6) Time servicing interrupts.
.TP
.IR softirq " (since Linux 2.6.0-test4)"
(7) Time servicing softirqs.
.TP
.IR steal " (since Linux 2.6.11)"
(8) Stolen time, which is the time spent in other operating systems when
running in a virtualized environment
.TP
.IR guest " (since Linux 2.6.24)"
(9) Time spent running a virtual CPU for guest
operating systems under the control of the Linux kernel.
.\" See Changelog entry for 5e84cfde51cf303d368fcb48f22059f37b3872de
.TP
.IR guest_nice " (since Linux 2.6.33)"
.\" commit ce0e7b28fb75cb003cfc8d0238613aaf1c55e797
(10) Time spent running a niced guest (virtual CPU for guest
operating systems under the control of the Linux kernel).
.RE
.TP
\fIpage 5741 1808\fP
The number of pages the system paged in and the number that were paged
out (from disk).
.TP
\fIswap 1 0\fP
The number of swap pages that have been brought in and out.
.TP
.\" FIXME The following is not the full picture for the 'intr' of
.\"       /proc/stat on 2.6:
\fIintr 1462898\fP
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;
each subsequent column is the total for a particular interrupt.
.TP
\fIdisk_io: (2,0):(31,30,5764,1,2) (3,0):\fP...
(major,disk_idx):(noinfo, read_io_ops, blks_read, write_io_ops, blks_written)
.br
(Linux 2.4 only)
.TP
\fIctxt 115315\fP
The number of context switches that the system underwent.
.TP
\fIbtime 769041601\fP
boot time, in seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
.TP
\fIprocesses 86031\fP
Number of forks since boot.
.TP
\fIprocs_running 6\fP
Number of processes in runnable state.
(Linux 2.5.45 onward.)
.TP
\fIprocs_blocked 2\fP
Number of processes blocked waiting for I/O to complete.
(Linux 2.5.45 onward.)
.RE
.TP
.I /proc/swaps
Swap areas in use.
See also
.BR swapon (8).
.TP
.I /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 \fI/proc\fP file system, and the (deprecated)
.BR sysctl (2)
system call.
.TP
.IR /proc/sys/abi " (since Linux 2.4.10)"
This directory may contain files with application binary information.
.\" On some systems, it is not present.
See the Linux kernel source file
.I Documentation/sysctl/abi.txt
for more information.
.TP
.I /proc/sys/debug
This directory may be empty.
.TP
.I /proc/sys/dev
This directory contains device-specific information (e.g.,
.IR dev/cdrom/info ).
On
some systems, it may be empty.
.TP
.I /proc/sys/fs
This directory contains the files and subdirectories for kernel variables
related to file systems.
.TP
.I /proc/sys/fs/binfmt_misc
Documentation for files in this directory can be found
in the Linux kernel sources in
.IR Documentation/binfmt_misc.txt .
.TP
.IR /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,
.IR nr_dentry ", " nr_unused ", " age_limit " (age in seconds), "
.I want_pages
(pages requested by system) and two dummy values.
.RS
.IP * 2
.I nr_dentry
is the number of allocated dentries (dcache entries).
This field is unused in Linux 2.2.
.IP *
.I nr_unused
is the number of unused dentries.
.IP *
.I age_limit
.\" looks like this is unused in kernels 2.2 to 2.6
is the age in seconds after which dcache entries
can be reclaimed when memory is short.
.IP *
.I want_pages
.\" looks like this is unused in kernels 2.2 to 2.6
is nonzero when the kernel has called shrink_dcache_pages() and the
dcache isn't pruned yet.
.RE
.TP
.I /proc/sys/fs/dir-notify-enable
This file can be used to disable or enable the
.I dnotify
interface described in
.BR fcntl (2)
on a system-wide basis.
A value of 0 in this file disables the interface,
and a value of 1 enables it.
.TP
.I /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.
.TP
.I /proc/sys/fs/dquot-nr
This file shows the number of allocated disk quota
entries and the number of free disk quota entries.
.TP
.IR /proc/sys/fs/epoll " (since Linux 2.6.28)"
This directory contains the file
.IR max_user_watches ,
which can be used to limit the amount of kernel memory consumed by the
.I epoll
interface.
For further details, see