| NAME | DESCRIPTION | NOTES | SEE ALSO | COLOPHON |
PROC(5) Linux Programmer's Manual PROC(5)
proc - process information pseudo-filesystem
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.
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]/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.
/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]/cmdline
This 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]/coredump_filter (since kernel 2.6.23)
See core(5).
/proc/[pid]/cpuset (since kernel 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 as
is being run by process [pid]. 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 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:
$ cat /proc/12015/fdinfo/4
pos: 1000
flags: 01002002
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 files in this directory are readable only by the owner of
the process.
/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]/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
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.
/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-super block 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.
/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:
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.
/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 information
about namespaces, see clone(2).
/proc/[pid]/ns/ipc (since Linux 3.0)
Bind mounting this file (see mount(2)) to somewhere else in
the filesystem keeps the IPC namespace of the process
specified by 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 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 setns(2).
/proc/[pid]/ns/net (since Linux 3.0)
Bind mounting this file (see mount(2)) to somewhere else in
the filesystem keeps the network namespace of the process
specified by 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 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 setns(2).
/proc/[pid]/ns/uts (since Linux 3.0)
Bind mounting this file (see mount(2)) to somewhere else in
the filesystem keeps the UTS namespace of the process
specified by 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 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 setns(2).
/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]/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]/smaps (since Linux 2.6.14)
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:
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
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, 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 CONFIG_MMU kernel
configuration option is enabled.
/proc/[pid]/stat
Status information about the process. This is used by ps(1).
It is defined in /usr/src/linux/fs/proc/array.c.
The fields, in order, with their proper scanf(3) format
specifiers, are:
pid %d (1) The process ID.
comm %s (2) The filename of the executable, in
parentheses. This is visible whether or not the
executable is swapped out.
state %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.
ppid %d (4) The PID of the parent.
pgrp %d (5) The process group ID of the process.
session %d (6) The session ID of the process.
tty_nr %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.)
tpgid %d (8) The ID of the foreground process group of the
controlling terminal of the process.
flags %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 include/linux/sched.h. Details depend
on the kernel version.
minflt %lu (10) The number of minor faults the process has
made which have not required loading a memory page
from disk.
cminflt %lu (11) The number of minor faults that the process's
waited-for children have made.
majflt %lu (12) The number of major faults the process has
made which have required loading a memory page
from disk.
cmajflt %lu (13) The number of major faults that the process's
waited-for children have made.
utime %lu (14) 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.
stime %lu (15) Amount of time that this process has been
scheduled in kernel mode, measured in clock ticks
(divide by sysconf(_SC_CLK_TCK)).
cutime %ld (16) 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).
cstime %ld (17) 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)).
priority %ld
(18) (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.
nice %ld (19) The nice value (see setpriority(2)), a value
in the range 19 (low priority) to -20 (high
priority).
num_threads %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.
itrealvalue %ld
(21) 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.
starttime %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
sysconf(_SC_CLK_TCK)).
vsize %lu (23) Virtual memory size in bytes.
rss %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.
rsslim %lu (25) Current soft limit in bytes on the rss of the
process; see the description of RLIMIT_RSS in
getrlimit(2).
startcode %lu
(26) The address above which program text can run.
endcode %lu (27) The address below which program text can run.
startstack %lu
(28) The address of the start (i.e., bottom) of
the stack.
kstkesp %lu (29) The current value of ESP (stack pointer), as
found in the kernel stack page for the process.
kstkeip %lu (30) The current EIP (instruction pointer).
signal %lu (31) 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.
blocked %lu (32) 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.
sigignore %lu
(33) 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.
sigcatch %lu
(34) 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.
wchan %lu (35) 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.
nswap %lu (36) Number of pages swapped (not maintained).
cnswap %lu (37) Cumulative nswap for child processes (not
maintained).
exit_signal %d (since Linux 2.1.22)
(38) Signal to be sent to parent when we die.
processor %d (since Linux 2.2.8)
(39) CPU number last executed on.
rt_priority %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 sched_setscheduler(2)).
policy %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
(41) Scheduling policy (see
sched_setscheduler(2)). Decode using the SCHED_*
constants in linux/sched.h.
delayacct_blkio_ticks %llu (since Linux 2.6.18)
(42) Aggregated block I/O delays, measured in
clock ticks (centiseconds).
guest_time %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
sysconf(_SC_CLK_TCK)).
cguest_time %ld (since Linux 2.6.24)
(44) Guest time of the process's children,
measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)).
/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
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
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)).
* 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).
* 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 kernel 2.6.26, see
capabilities(7)).
* 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_context_switches, nonvoluntary_context_switches:
Number of voluntary and involuntary context switches (since
Linux 2.6.23).
/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]/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/bus
Contains subdirectories for installed busses.
/proc/bus/pccard
Subdirectory for PCMCIA devices when CONFIG_PCMCIA is set at
kernel compilation time.
/proc/[pid]/timers (since Linux 3.10)
A list of the POSIX timers for this process. Each timer is
listed with a line that starets 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.sival_ptr 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 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
dexposed 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.
/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/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
Empty subdirectory.
/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/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 fileds 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 mmaped, 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)
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 /proc/sys/vm/overcommit_ratio). The
CommitLimit is calculated using the following formula:
CommitLimit =
([total RAM pages] - [total huge TLB pages]) *
overcommit_ratio / 100 + [total swap pages]
For example, on a system with 1GB of physical RAM and
7GB of swap with a overcommit_ratio of 30, this formula
yields a CommitLimit of 7.3GB. For more details, see
the memory overcommit documentation in 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
/proc/sys/vm/overcommit_memory), allocations which
would exceed the 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.
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 only useful 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
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.
/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; each subsequent column is the total for a
particular interrupt.
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.
/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. (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
The kernel constant NR_OPEN imposes an upper limit on the
value that may be placed in 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/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
behaviour 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:
+o the target is a regular file;
+o the target file does not have its set-user-ID
permission bit enabled;
+o the target file does not have both its set-group-ID and
group-executable permission bits enabled; and
+o 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
behaviour 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 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 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/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(8) 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
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.
/proc/sys/kernel/msgmnb
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).
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
The four values in this file are console_loglevel,
default_message_loglevel, minimum_console_level, and
default_console_loglevel. These values influence printk()
behavior when printing or logging error messages. See
syslog(2) for more info on the different loglevels. Messages
with a higher priority than console_loglevel will be printed
to the console. Messages without an explicit priority will be
printed with priority default_message_level.
minimum_console_loglevel is the minimum (highest) value to
which console_loglevel can be set. default_console_loglevel
is the default value for console_loglevel.
/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/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/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
This file contains the system-wide limit on the total number
of pages of System V shared memory.
/proc/sys/kernel/shmmax
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/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 signalling 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 like:
#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 behind 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.
/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/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/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(8)
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_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 on the system is
limited to (SS + RAM*(r/100)), where SS is the size of the
swap space, and RAM is the size of the physical memory, and r
is the contents of the file /proc/sys/vm/overcommit_ratio.
/proc/sys/vm/overcommit_ratio
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/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)
This file displays various virtual memory statistics.
/proc/zoneinfo (since Linux 2.6.13)
This file display information about memory zones. This is
useful for analyzing virtual memory behavior.
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.
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),
time(7), arp(8), hdparm(8), ifconfig(8), init(8), lsmod(8), lspci(8),
mount(8), netstat(8), procinfo(8), route(8), sysctl(8)
The Linux kernel source files: Documentation/filesystems/proc.txt and
Documentation/sysctl/vm.txt.
This page is part of release 3.57 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2014-01-20 PROC(5)
Copyright and license for this manual page
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