- /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
null-separated strings,
with a further null byte (aq\0aq) 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 (aq\0aq),
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 aq\000aq aq\naq
- /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 t0 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 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
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.
- *
-
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(8)
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/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/modules
-
A text list of the modules that have been loaded by the system.
See also
lsmod(8).
- /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 pre-programmed 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 non-optionally 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 aqscsi add-single-device 1 0 5 0aq > /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,minor):(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 (January 1, 1970).
- 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.
Presently, there are subdirectories
abi, debug, dev, fs, kernel, net, proc,
rxrpc, sunrpc and vm
that each contain more files and subdirectories.
- /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 contains the subdirectories
binfmt_misc, inotify, and mqueue,
and files
dentry-state, dir-notify-enable, dquot-nr, file-max,
file-nr, inode-max, inode-nr, inode-state,
lease-break-time, leases-enable,
overflowgid, overflowuid,
suid_dumpable,
super-max, and super-nr.
- /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 non-zero 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/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 non-zero 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 non-zero 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/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 aqdarkstaraq > /proc/sys/kernel/hostname
# echo aqmydomainaq > /proc/sys/kernel/domainname
has the same effect as
# hostname aqdarkstaraq
# domainname aqmydomainaq
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 non-zero 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 non-zero.
- /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 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 non-zero
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 non-zero 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
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 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 onwards)
This file
specifies the system-wide maximum number of System V shared memory
segments that can be created.
- /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 (non-zero), 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 non-destructive 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 non-zero, this disables the new 32-bit memory-mapping layout;
the kernel will use the legacy (2.4) layout for all processes.
- /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 non-zero, 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 non-zero, 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 non-zero, 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 non-zero 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/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.
This manual page is incomplete, possibly inaccurate, and is the kind
of thing that needs to be updated very often.
