PROC(5) Linux Programmer's Manual PROC(5)
NAME
proc - process information pseudo-file system
DESCRIPTION
The proc file system is a pseudo-file system which is used as an inter-
face 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 outline gives a quick tour through 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]/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 charac-
ters. 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:
$ (cat /proc/1/environ; echo) | tr '\000' '\n'
/proc/[pid]/exe
Under Linux 2.2 and later, this file is a symbolic link contain-
ing 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 sym-
bolic link are not available if the main thread has already ter-
minated (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, etc.
In a multithreaded process, the contents of this directory are
not available if the main thread has already terminated (typi-
cally 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 argu-
ment, 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, assum-
ing 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 symboli-
cally 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 con-
tents 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 off-
set. 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]/limits (since kernel 2.6.24)
This file displays the soft limit, hard limit, and units of mea-
surement for each of the process's resource limits (see getr-
limit(2)). The file is protected to only allow reading by the
real UID of the process.
/proc/[pid]/maps
A file containing the currently mapped memory regions and their
access permissions.
The format is:
address perms offset dev inode pathname
08048000-08056000 r-xp 00000000 03:0c 64593 /usr/sbin/gpm
08056000-08058000 rw-p 0000d000 03:0c 64593 /usr/sbin/gpm
08058000-0805b000 rwxp 00000000 00:00 0
40000000-40013000 r-xp 00000000 03:0c 4165 /lib/ld-2.2.4.so
40013000-40015000 rw-p 00012000 03:0c 4165 /lib/ld-2.2.4.so
4001f000-40135000 r-xp 00000000 03:0c 45494 /lib/libc-2.2.4.so
40135000-4013e000 rw-p 00115000 03:0c 45494 /lib/libc-2.2.4.so
4013e000-40142000 rw-p 00000000 00:00 0
bffff000-c0000000 rwxp 00000000 00:00 0
where "address" is the address space in the process that it
occupies, "perms" is a set of permissions:
r = read
w = write
x = execute
s = shared
p = private (copy on write)
"offset" is the offset into the file/whatever, "dev" is the
device (major:minor), and "inode" is the inode on that device.
0 indicates that no inode is associated with the memory region,
as the case would be with BSS (uninitialized data).
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 file system (see
stat(2)).
(4) root: root of the mount within the file system.
(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) file system type: name of file system in the form
"type[.subtype]".
(10) mount source: file system-specific information or "none".
(11) super options: per-super block options.
Parsers should ignore all unrecognized optional fields. Cur-
rently 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 "mas-
ter:X" field is present and not the "propagate_from:X" field.
For more information on mount propagation see: Documenta-
tion/filesystems/sharedsubtree.txt in the kernel source tree.
/proc/[pid]/mounts (since Linux 2.4.19)
This is a list of all the file systems currently mounted in the
process's mount namespace. The format of this file is docu-
mented 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 file system 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 infor-
mation) 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 file system tree.
(3) The file system type.
(4) Optional statistics and configuration information. Cur-
rently (as at Linux 2.6.26), only NFS file systems export
information via this field.
This file is only readable by the owner of the process.
/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 set-
ting. A process must be privileged (CAP_SYS_RESOURCE) to update
this file.
/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 bit-shift adjustment specified
by the oom_adj setting for the process.
/proc/[pid]/root
Unix and Linux support the idea of a per-process root of the
file system, set by the chroot(2) system call. This file is a
symbolic link that points to the process's root directory, and
behaves as exe, fd/*, etc. do.
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 dis-
played 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 only present 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 speci-
fiers, are:
pid %d The process ID.
comm %s The filename of the executable, in parentheses.
This is visible whether or not the executable is
swapped out.
state %c 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 zom-
bie, T is traced or stopped (on a signal), and W is
paging.
ppid %d The PID of the parent.
pgrp %d The process group ID of the process.
session %d The session ID of the process.
tty_nr %d The controlling terminal of the process. (The minor
device number is contained in the combination of
bits 31 to 20 and 7 to 0; the major device number is
in bits 15 to 8.)
tpgid %d The ID of the foreground process group of the con-
trolling terminal of the process.
flags %u (%lu before Linux 2.6.22)
The kernel flags word of the process. For bit mean-
ings, see the PF_* defines in <linux/sched.h>.
Details depend on the kernel version.
minflt %lu The number of minor faults the process has made
which have not required loading a memory page from
disk.
cminflt %lu The number of minor faults that the process's
waited-for children have made.
majflt %lu The number of major faults the process has made
which have required loading a memory page from disk.
cmajflt %lu The number of major faults that the process's
waited-for children have made.
utime %lu Amount of time that this process has been scheduled
in user mode, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK). This includes guest time,
guest_time (time spent running a virtual CPU, see
below), so that applications that are not aware of
the guest time field do not lose that time from
their calculations.
stime %lu Amount of time that this process has been scheduled
in kernel mode, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK).
cutime %ld Amount of time that this process's waited-for chil-
dren 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 Amount of time that this process's waited-for chil-
dren have been scheduled in kernel mode, measured in
clock ticks (divide by sysconf(_SC_CLK_TCK).
priority %ld
(Explanation for Linux 2.6) For processes running a
real-time scheduling policy (policy below; see
sched_setscheduler(2)), this is the negated schedul-
ing priority, minus one; that is, a number in the
range -2 to -100, corresponding to real-time priori-
ties 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 The nice value (see setpriority(2)), a value in the
range 19 (low priority) to -20 (high priority).
num_threads %ld
Number of threads in this process (since Linux 2.6).
Before kernel 2.6, this field was hard coded to 0 as
a placeholder for an earlier removed field.
itrealvalue %ld
The time in jiffies before the next SIGALRM is sent
to the process due to an interval timer. Since ker-
nel 2.6.17, this field is no longer maintained, and
is hard coded as 0.
starttime %llu (was %lu before Linux 2.6)
The time in jiffies the process started after system
boot.
vsize %lu Virtual memory size in bytes.
rss %ld Resident Set Size: number of pages the process has
in real memory. This is just the pages which count
towards text, data, or stack space. This does not
include pages which have not been demand-loaded in,
or which are swapped out.
rsslim %lu Current soft limit in bytes on the rss of the
process; see the description of RLIMIT_RSS in get-
priority(2).
startcode %lu
The address above which program text can run.
endcode %lu The address below which program text can run.
startstack %lu
The address of the start (i.e., bottom) of the
stack.
kstkesp %lu The current value of ESP (stack pointer), as found
in the kernel stack page for the process.
kstkeip %lu The current EIP (instruction pointer).
signal %lu The bitmap of pending signals, displayed as a deci-
mal number. Obsolete, because it does not provide
information on real-time signals; use
/proc/[pid]/status instead.
blocked %lu The bitmap of blocked signals, displayed as a deci-
mal number. Obsolete, because it does not provide
information on real-time signals; use
/proc/[pid]/status instead.
sigignore %lu
The bitmap of ignored signals, displayed as a deci-
mal number. Obsolete, because it does not provide
information on real-time signals; use
/proc/[pid]/status instead.
sigcatch %lu
The bitmap of caught signals, displayed as a decimal
number. Obsolete, because it does not provide
information on real-time signals; use
/proc/[pid]/status instead.
wchan %lu This is the "channel" in which the process is wait-
ing. It is the address of a system call, and can be
looked up in a namelist if you need a textual name.
(If you have an up-to-date /etc/psdatabase, then try
ps -l to see the WCHAN field in action.)
nswap %lu Number of pages swapped (not maintained).
cnswap %lu Cumulative nswap for child processes (not main-
tained).
exit_signal %d (since Linux 2.1.22)
Signal to be sent to parent when we die.
processor %d (since Linux 2.2.8)
CPU number last executed on.
rt_priority %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
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)
Scheduling policy (see sched_setscheduler(2)).
Decode using the SCHED_* constants in linux/sched.h.
delayacct_blkio_ticks %llu (since Linux 2.6.18)
Aggregated block I/O delays, measured in clock ticks
(centiseconds).
guest_time %lu (since Linux 2.6.24)
Guest time of the process (time spent running a vir-
tual CPU for a guest operating system), measured in
clock ticks (divide by sysconf(_SC_CLK_TCK).
cguest_time %ld (since Linux 2.6.24)
Guest time of the process's children, measured in
clock ticks (divide by sysconf(_SC_CLK_TCK).
/proc/[pid]/statm
Provides information about memory usage, measured in pages. The
columns are:
size total program size
(same as VmSize in /proc/[pid]/status)
resident resident set size
(same as VmRSS in /proc/[pid]/status)
share shared pages (from shared mappings)
text text (code)
lib library (unused in Linux 2.6)
data data + stack
dt 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)).
* TracerPid: PID of process tracing this process (0 if not being
traced).
* Uid, Gid: Real, effective, saved set, and file system 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.
* 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.
* 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 capabili-
ties(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] direc-
tories. For attributes that are shared by all threads, the con-
tents 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 ter-
minated (typically by calling pthread_exit(3)).
/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/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 configur-
ing the kernel (using make xconfig, make config, or similar).
The file contents are compressed; view or search them using
zcat(1), zgrep(1), etc. 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 only provided 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.
/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 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 file systems which are supported by the
kernel, namely file systems which were compiled into the kernel
or whose kernel modules are currently loaded. (See also
filesystems(5).) If a file system is marked with "nodev", this
means that it does not require a block device to be mounted
(e.g., virtual file system, network file system).
Incidentally, this file may be used by mount(8) when no file
system is specified and it didn't manage to determine the file
system type. Then file systems contained in this file are tried
(excepted those that are marked with "nodev").
/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 architec-
tures, 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 dif-
ferent 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 mes-
sages.
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 sepa-
rated by a slash (/). The first of these is the number of cur-
rently executing kernel scheduling entities (processes,
threads); this will be less than or equal to the number of CPUs.
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 only present 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 mem-
ory (both physical and swap) on the system as well as the shared
memory and buffers used by the kernel.
/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 file sys-
tems 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 docu-
mented in fstab(5).
/proc/mtrr
Memory Type Range Registers. See the kernel source file Docu-
mentation/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 struc-
tures 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 ker-
nel 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 ker-
nel 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 inter-
nal 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 cre-
ator 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 ker-
nel 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 inter-
nal 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 data-
gram 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 major and minor numbers of each partition as well as
number of blocks and partition name.
/proc/pci
This is a listing of all PCI devices found during kernel ini-
tialization 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 CON-
FIG_PCI_LEGACY_PROC set), and finally removed altogether since
Linux 2.6.17.
/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 sub-
system 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 cur-
rently 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 reg-
istered 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 configura-
tion, statistics, etc.
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 file
system, 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 only present 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 user mode, user mode with low priority
(nice), system mode, and the idle task, respectively.
The last value should be USER_HZ times the second entry
in the uptime pseudo-file.
In Linux 2.6 this line includes three additional columns:
iowait - time waiting for I/O to complete (since 2.5.41);
irq - time servicing interrupts (since 2.6.0-test4);
softirq - time servicing softirqs (since 2.6.0-test4).
Since Linux 2.6.11, there is an eighth column, steal -
stolen time, which is the time spent in other operating
systems when running in a virtualized environment
Since Linux 2.6.24, there is a ninth column, guest, which
is the time spent running a virtual CPU for guest operat-
ing 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
onwards.)
procs_blocked 2
Number of processes blocked waiting for I/O to complete.
(Linux 2.5.45 onwards.)
/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
file system, and the (deprecated) sysctl(2) system call.
/proc/sys/abi (since Linux 2.4.10)
This directory may contain files with application binary infor-
mation. See the 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 file systems.
/proc/sys/fs/binfmt_misc
Documentation for files in this directory can be found in the
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 about running out of file handles, 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.
If you increase /proc/sys/fs/file-max, be sure to increase
/proc/sys/fs/inode-max to 3-4 times the new value of
/proc/sys/fs/file-max, or you will run out of inodes.
/proc/sys/fs/file-nr
This (read-only) file gives the number of files presently
opened. It contains three numbers: the number of allocated file
handles; the number of free file handles; and the maximum number
of file handles. The kernel allocates file handles dynamically,
but it doesn't free them again. If the number of allocated
files is close to the maximum, you should consider increasing
the maximum. When the number of free file handles is large,
you've encountered a peak in your usage of file handles and you
probably don't need to increase the maximum.
/proc/sys/fs/inode-max
This file contains the maximum number of in-memory inodes. On
some (2.4) systems, it may not be present. 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.
/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. nr_inodes is the number of
inodes the system has allocated. This can be slightly more than
inode-max because Linux allocates them one page full at a time.
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.
/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 inter-
face. 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 sig-
nal to that process notifying it that another process is waiting
to open the file. If the lease holder does not remove or down-
grade 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 file systems only support
16-bit UIDs and GIDs, although in Linux UIDs and GIDs are 32
bits. When one of these file systems 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/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 bina-
ries. 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 file system user ID of the dumping process
and no security is applied. This is intended for system debug-
ging 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 adminis-
trators are attempting to debug problems in a normal environ-
ment.
/proc/sys/fs/super-max
This file controls the maximum number of superblocks, and thus
the maximum number of mounted file systems the kernel can have.
You only need to increase super-max if you need to mount more
file systems than the current value in super-max allows you to.
/proc/sys/fs/super-nr
This file contains the number of file systems 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 fre-
quency. If BSD-style process accounting is enabled these values
control its behavior. If free space on file system 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-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 capabil-
ity 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 key-
board. 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, with-
out 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/hotplug
This file contains the path for the hotplug policy agent. The
default value in this file is /sbin/hotplug.
/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 host-
name "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/htab-reclaim
(PowerPC only) If this file is set to a nonzero value, the Pow-
erPC htab (see kernel file Documentation/powerpc/ppc_htab.txt)
is pruned each time the system hits the idle loop.
/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 only present if
the kernel is built with the CONFIG_KMOD option enabled. It is
described by the kernel source file Documentation/kmod.txt (only
present in kernel 2.4 and earlier).
/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 mes-
sage queue.
/proc/sys/kernel/msgmni
This file defines the system-wide limit on the number of message
queue identifiers. (This file is only present in Linux 2.4
onwards.)
/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/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 watch-
dog 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_mes-
sage_loglevel, minimum_console_level, and default_con-
sole_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 con-
sole_loglevel.
/proc/sys/kernel/pty (since Linux 2.6.4)
This directory contains two files relating to the number of Unix
98 pseudo-terminals (see pts(4)) on the system.
/proc/sys/kernel/pty/max
This file defines the maximum number of pseudo-terminals.
/proc/sys/kernel/pty/nr
This read-only file indicates how many pseudo-terminals are cur-
rently in use.
/proc/sys/kernel/random
This directory contains various parameters controlling the oper-
ation of the file /dev/random. See random(4) for further infor-
mation.
/proc/sys/kernel/real-root-dev
This file is documented in the kernel source file Documenta-
tion/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/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/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
(available in Linux 2.4 and onwards) 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 specifi-
cally 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 - bitmask 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 only present if the CONFIG_MAGIC_SYSRQ kernel con-
figuration option is enabled. For further details see the ker-
nel 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
file system (NFS). On some systems, it is not present.
/proc/sys/vm
This directory contains files for memory management tuning, buf-
fer 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.
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 this 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 han-
dled 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 affect-
ing any applications. But if there is no other up-to-date copy
of the data, it will kill processes to prevent any data corrup-
tions from propagating.
The file has one of the following values:
1: Kill all processes that have the corrupted-and-not-reload-
able 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 only
kill a process who 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 only active 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_MEM-
ORY_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_MEM-
ORY_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 pos-
sibly 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_allocat-
ing_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 get-
ting 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 sit-
uation.
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 agressiveness, 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 func-
tion as typing ALT-SysRq-<character> (see the description of
/proc/sys/kernel/sysrq). This file is normally only writable by
root. For further details see the kernel source file Documenta-
tion/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 (sec-
onds), and the amount of time spent in idle process (seconds).
/proc/version
This string identifies the kernel version that is currently run-
ning. 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 use-
ful for analyzing virtual memory behavior.
NOTES
Many strings (i.e., the environment and command line) are in the inter-
nal format, with subfields terminated by null bytes ('\0'), so you may
find that things are more readable if you use od -c or tr "\000" "\n"
to read them. Alternatively, echo `cat <file>` works well.
This manual page is incomplete, possibly inaccurate, and is the kind of
thing that needs to be updated very often.
SEE ALSO
cat(1), dmesg(1), find(1), free(1), ps(1), tr(1), uptime(1), chroot(2),
mmap(2), readlink(2), syslog(2), slabinfo(5), hier(7), time(7), arp(8),
hdparm(8), ifconfig(8), init(8), lsmod(8), lspci(8), mount(8), net-
stat(8), procinfo(8), route(8)
The kernel source files: Documentation/filesystems/proc.txt, Documenta-
tion/sysctl/vm.txt
COLOPHON
This page is part of release 3.27 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 2010-06-19 PROC(5)
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