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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/[number]/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/[number]/coredump_filter (since kernel 2.6.23)
              See core(5).

              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"

              (For a reason why one should want to do  this,  see  lilo(8)  or

              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/[number]/exe to run another copy of the same executable as
              is being run by process [number].  In a  multithreaded  process,
              the contents of this symbolic link are not available if the main
              thread   has   already   terminated   (typically   by    calling

              Under  Linux  2.0 and earlier /proc/[number]/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/[number]/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/[number]/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/[number]/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/[number]/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 stat(2)).

                   (4)  root: root of the mount within the file system.

                   (5)  mount  point:  mount  point  relative to the process’s

                   (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

                   (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/[number]/mountstats (since Linux 2.6.17)
              This  file system 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/[number]/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/[number]/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/[number]/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/[number]/maps.  The remaining
              lines  show  the  size of the mapping, the amount of the mapping
              that is currently resident in RAM, the number  clean  and  dirty
              shared  pages  in  the  mapping,  and the number 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/[number]/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/[number]/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/[number]/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/[number]/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/[number]/status)
                  resident   resident set size
                             (same as VmRSS in /proc/[number]/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/[number]/stat  and
              /proc/[number]/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/[number]/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 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/[number] directories.  For
              attributes that are shared by all threads, the contents for each
              of  the  files under the task/[thread-ID] subdirectories will be
              the  same  as  in  the  corresponding   file   in   the   parent
              /proc/[number]  directory (e.g., in a multithreaded process, all
              of the task/[thread-ID]/cwd files will have the  same  value  as
              the  /proc/[number]/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/[thread-ID] may have  different  values  (e.g.,
              various  fields in each of the task/[thread-ID]/status files may
              be different for each thread).

              In   a   multithreaded   process,   the    contents    of    the
              /proc/[number]/task  directory  are  not  available  if the main
              thread   has   already   terminated   (typically   by    calling

              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).

              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 for each IRQ on
              (at least) the i386 architecture.  Very easy to read formatting,
              done in ASCII.

              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(8) 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  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.

              It is in the same format as free(1).

              This  is a list of all the file systems currently mounted on the
              system.  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.

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

              Memory        Type         Range         Registers.          See
              /usr/src/linux/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 pre-programmed 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 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.

              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,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

              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 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,  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   non-zero   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.

              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 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).

              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 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

              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  acct,  cad_pid,  cap-bound,
              core_pattern,   core_uses_pid,    ctrl-alt-del,    dentry-state,
              domainname,  hotplug,  hostname,  htab-reclaim  (PowerPC  only),
              java-appletviewer  (binfmt_java,   obsolete),   java-interpreter
              (binfmt_java,  obsolete), l2cr (PowerPC only), modprobe, msgmax,
              msgmnb, msgmni,  osrelease,  ostype,  overflowgid,  overflowuid,
              panic,  panic_on_oops,  pid_max,  powersave-nap  (PowerPC only),
              printk, pty, random,  real-root-dev,  reboot-cmd  (SPARC  only),
              rtsig-max,  rtsig-nr,  sem, sg-big-buff, shmall, shmmax, shmmni,
              sysrq, tainted, threads-max, version,  and  zero-paged  (PowerPC

              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%  of  space  is  free;
              resume  it if >= 4% of 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 > 0, 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.

              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 non-zero 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 non-zero.

              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  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.

              This file (new in Linux 2.5) 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.

              This file (new in Linux 2.5) 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_leveland
              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 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/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

              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 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 disable the new 32-bit memory-mapping  layout;
              the kernel will use the legacy (2.4) layout for all processes.

              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  set  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.

              See the description of /proc/sys/vm/overcommit_memory.

              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 sub-fields 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), 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),
       dmesg(8),  hdparm(8),   ifconfig(8),   init(8),   lsmod(8),   lspci(8),
       mount(8), netstat(8), procinfo(8), route(8)


       This  page  is  part of release 3.01 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at