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       proc - process information pseudo-file system


       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

       The following outline gives a quick tour through the /proc hierarchy.

              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.

              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 ('\0')
              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).

              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)).

              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'

              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:


              For example, [0301]:1502 would be inode 1502 on device major  03
              (IDE,  MFM,  etc. drives) minor 01 (first partition on the first

              find(1) with the -inum option can be used to locate the file.

              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

                  $ 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.

              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/
              40013000-40015000 rw-p 00012000 03:0c 4165    /lib/
              4001f000-40135000 r-xp 00000000 03:0c 45494   /lib/
              40135000-4013e000 rw-p 00115000 03:0c 45494   /lib/
              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.

              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

              (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

              (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

              (8)  separator: marks the end of the optional fields.

              (9)  file  system  type:  name  of  file  system  in  the   form

              (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"

              For    more    information    on    mount    propagation    see:
              Documentation/filesystems/sharedsubtree.txt in the kernel source

       /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.

              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.

              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

              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

              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

              cstime %ld  Amount  of  time  that  this  process’s   waited-for
                          children   have   been  scheduled  in  kernel  mode,
                          measured    in    clock     ticks     (divide     by

              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

              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

              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

              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

              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

              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

              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).

              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)

              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

              * Uid,  Gid:  Real,  effective,  saved set, and file system UIDs

              * 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

              * CapBnd: Capability Bounding  set  (since  kernel  2.6.26,  see

              * 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)).

              Advanced power management version and battery  information  when
              CONFIG_APM is defined at kernel compilation time.

              Contains subdirectories for installed busses.

              Subdirectory  for  PCMCIA  devices  when CONFIG_PCMCIA is set at
              kernel compilation time.


              Contains various bus subdirectories and pseudo-files  containing
              information  about  PCI  busses,  installed  devices, and device
              drivers.  Some of these files are not ASCII.

              Information about PCI devices.  They  may  be  accessed  through
              lspci(8) and setpci(8).

              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.

              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.

              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

              This  is a list of the registered ISA DMA (direct memory access)
              channels in use.

              Empty subdirectory.

              List of the execution domains (ABI personalities).

              Frame buffer information when CONFIG_FB is defined during kernel

              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").

              Empty subdirectory.

              This  directory  exists  on systems with the IDE bus.  There are
              directories for each IDE channel  and  attached  device.   Files

                  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.

              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

              I/O memory map in Linux 2.4.

              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.

              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.

              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

              Information in this file is retrieved with the dmesg(1) program.

       /proc/ksyms (Linux 1.1.23-2.5.47)
              See /proc/kallsyms.

              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

              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.

              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.

              A  text list of the modules that have been loaded by the system.
              See also lsmod(8).

              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).

              Memory  Type  Range  Registers.   See  the  kernel  source  file
              Documentation/mtrr.txt for details.

              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.

              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   0x1       0x2       00:50:BF:25:68:F3   *      eth0  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.

              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

              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

              Internet    Group    Management    Protocol.      Defined     in

              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.

              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.

              This file holds the ASCII data needed for the IP, ICMP, TCP, and
              UDP management information bases for an SNMP agent.

              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.

              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

              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.

              Contains  major  and  minor numbers of each partition as well as
              number of blocks and partition name.

              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.

              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.

              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

              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.

              [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.

              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.

              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:


              See slabinfo(5) for details.

              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

              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

              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

              procs_blocked 2
                     Number of processes blocked waiting for I/O to  complete.
                     (Linux 2.5.45 onwards.)

              Swap areas in use.  See also swapon(8).

              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

       /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.

              This directory may be empty.

              This   directory  contains  device-specific  information  (e.g.,
              dev/cdrom/info).  On some systems, it may be empty.

              This contains the subdirectories  binfmt_misc,  epoll,  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.

              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.

              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.

              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

              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).

              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

              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.

              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.

              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.

              This file contains the first two values from 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).

              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.

              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/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

              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.

              This file contains the number of file systems currently mounted.

              This  directory  contains  files  controlling  a range of kernel
              parameters, as described below.

              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).

              See core(5).

              See core(5).

              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

              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  has  the
              hostname  "darkstar"  and  DNS  (Internet  Domain  Name  Server)
              domainname "", 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.

              (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.

              (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.

              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).

              This file defines a system-wide  limit  specifying  the  maximum
              number  of  bytes  in  a  single  message  written on a System V
              message queue.

              This file defines the system-wide limit on the number of message
              queue  identifiers.   (This  file  is  only present in Linux 2.4

              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

              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.

              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

       /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.

              This file defines the maximum number of pseudo-terminals.

              This  read-only  file  indicates  how  many pseudo-terminals are
              currently in use.

              This  directory  contains  various  parameters  controlling  the
              operation  of  the  file /dev/random.  See random(4) for further

              This  file   is   documented   in   the   kernel   source   file

       /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

              (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.

              (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

              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.

              This file contains the system-wide limit on the total number  of
              pages of System V shared memory.

              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.

              (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.

              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-
                      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.

              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

              This directory contains networking stuff.  Explanations for some
              of the files under this directory can be  found  in  tcp(7)  and

              This  file  defines  a ceiling value for the backlog argument of
              listen(2); see the listen(2) manual page for details.

              This directory may be empty.

              This directory supports Sun remote procedure  call  for  network
              file system (NFS).  On some systems, it is not present.

              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

              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   >

              Because this is a nondestructive operation and dirty objects are
              not freeable, the user should run sync(8) first.

              The value in this file controls how aggressively the kernel will
              swap  memory pages.  Higher values increase agressiveness, lower
              values descrease aggressiveness.  The default value is 60.

       /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/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

              The default value is 0.

              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.

              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

              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/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

              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.

              Subdirectory  containing the pseudo-files and subdirectories for
              tty drivers and line disciplines.

              This file  contains  two  numbers:  the  uptime  of  the  system
              (seconds),  and  the  amount  of  time  spent  in  idle  process

              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
            Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994

       /proc/vmstat (since Linux 2.6)
              This file displays various virtual memory statistics.

       /proc/zoneinfo (since Linux 2.6.13)
              This  file  display  information  about  memory  zones.  This is
              useful for analyzing virtual memory behavior.


       Many strings (i.e., the  environment  and  command  line)  are  in  the
       internal format, with subfields terminated by null bytes ('\0'), so you
       may find that things are more readable if you use od -c  or  tr  "\000"
       "\n" to read them.  Alternatively, echo `cat <file>` works well.

       This manual page is incomplete, possibly inaccurate, and is the kind of
       thing that needs to be updated very often.


       cat(1), dmesg(1), find(1), free(1), ps(1), tr(1), uptime(1), chroot(2),
       mmap(2), readlink(2), syslog(2), slabinfo(5), hier(7), time(7), arp(8),
       hdparm(8),  ifconfig(8),   init(8),   lsmod(8),   lspci(8),   mount(8),
       netstat(8), procinfo(8), route(8)
       The    kernel    source    files:   Documentation/filesystems/proc.txt,


       This page is part of release 3.24 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at