Process Info (proc)
NAME
proc - process information pseudo-file system
DESCRIPTION
The proc file system is a pseudo-file system which is used as 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 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 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:
$ (cat /proc/1/environ; echo) | tr '\000' '\n'
/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, etc.
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]/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)). 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. 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 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 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 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 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 file system tree.
(3) The file system type.
(4) Optional statistics and configuration information. Currently (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
setting. 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 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 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 specifiers,
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 zombie, 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 controlling
terminal of the process.
flags %u (%lu before Linux 2.6.22)
The kernel flags word of the process. For bit meanings,
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 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 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
(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 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 kernel 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 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 Current soft limit in bytes on the rss of the process; see
the description of RLIMIT_RSS in getpriority(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 decimal
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 decimal
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 decimal
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 waiting. It
is the address of a system call, and can be looked up in a
namelist if you need a textual name. (If you have an up-
to-date /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 maintained).
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 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)
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 (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.
* 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/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 configuring 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 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 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 memory (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 systems
currently mounted on the system. With the introduction of per-process
mount namespaces in Linux 2.4.19, this file became a link to
/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 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 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 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/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, 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 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 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 information.
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 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 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 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 file system 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.
/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 frequency.
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 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/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 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/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/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 message 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 onward.)
/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 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 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/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 onward) 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 - 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
configuration option is enabled. For further details see the 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 file
system (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.
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 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 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_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 only writable by root.
For further details see the 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.
NOTES
Many strings (i.e., the environment and command line) are in the internal
format, with subfields terminated by null bytes ('\0'), so you may find that
things are more readable if you use od -c or tr "\000" "\n" to read them.
Alternatively, echo `cat <file>` works well.
This manual page is incomplete, possibly inaccurate, and is the kind of thing
that needs to be updated very often.
SEE ALSO
cat(1), dmesg(1), find(1), free(1), ps(1), tr(1), uptime(1), chroot(2),
mmap(2), readlink(2), syslog(2), slabinfo(5), hier(7), time(7), arp(8),
hdparm(8), ifconfig(8), init(8), lsmod(8), lspci(8), mount(8), netstat(8),
procinfo(8), route(8)
The kernel source files: Documentation/filesystems/proc.txt,
Documentation/sysctl/vm.txt
COLOPHON
This page is part of release 3.32 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/.