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PROC(5)                    Linux Programmer's Manual                   PROC(5)

       proc - process information pseudo-file system

       The proc file system is a pseudo-file system which is used as an inter-
       face to kernel data structures.  It is commonly mounted at /proc.  Most
       of  it  is  read-only,  but  some  files  allow  kernel variables to be

       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 charac-
              ters.  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).

       /proc/[number]/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"

              (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 contain-
              ing the actual pathname of the executed command.  This  symbolic
              link  can  be  dereferenced normally; attempting to open it will
              open the executable.  You can even  type  /proc/[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 pthread_exit(3)).

              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 (typi-
              cally by calling pthread_exit(3)).

              Programs that will take a filename as a  command-line  argument,
              but  will  not  take input from standard input if no argument is
              supplied, or that write to a file named as a command-line  argu-
              ment,  but  will  not send their output to standard output if no
              argument is supplied, can nevertheless be made to  use  standard
              input  or  standard  out  using /proc/[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 symboli-
              cally link /dev/fd to /proc/self/fd, in fact.

              Most systems provide symbolic links /dev/stdin, /dev/stdout, and
              /dev/stderr, which respectively link to the files 0, 1, and 2 in
              /proc/self/fd.   Thus the example command above could be written

                  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 con-
              tents of each file can be read to obtain information  about  the
              corresponding file descriptor, for example:

                  $ cat /proc/12015/fdinfo/4
                  pos:    1000
                  flags:  01002002

              The  pos field is a decimal number showing the current file off-
              set.  The flags field is an octal number that displays the  file
              access mode and file status flags (see open(2)).

              The  files  in  this directory are readable only by the owner of
              the process.

       /proc/[number]/limits (since kernel 2.6.24)
              This file displays the soft limit, hard limit, and units of mea-
              surement  for  each  of the process's resource limits (see getr-
              limit(2)).  The file is protected to only allow reading  by  the
              real UID of the process.

              A  file containing the currently mapped memory regions and their
              access permissions.

              The format is:

        address           perms offset  dev   inode      pathname
        08048000-08056000 r-xp 00000000 03:0c 64593      /usr/sbin/gpm
        08056000-08058000 rw-p 0000d000 03:0c 64593      /usr/sbin/gpm
        08058000-0805b000 rwxp 00000000 00:00 0
        40000000-40013000 r-xp 00000000 03:0c 4165       /lib/ld-2.2.4.so
        40013000-40015000 rw-p 00012000 03:0c 4165       /lib/ld-2.2.4.so
        4001f000-40135000 r-xp 00000000 03:0c 45494      /lib/libc-2.2.4.so
        40135000-4013e000 rw-p 00115000 03:0c 45494      /lib/libc-2.2.4.so
        4013e000-40142000 rw-p 00000000 00:00 0
        bffff000-c0000000 rwxp 00000000 00:00 0

              where "address" is the address space  in  the  process  that  it
              occupies, "perms" is a set of permissions:

                   r = read
                   w = write
                   x = execute
                   s = shared
                   p = private (copy on write)

              "offset"  is  the  offset  into  the file/whatever, "dev" is the
              device (major:minor), and "inode" is the inode on  that  device.
              0  indicates that no inode is associated with the memory region,
              as the case would be with BSS (uninitialized data).

              Under Linux 2.0 there is no field giving pathname.

              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.   Cur-
              rently the possible optional fields are:

                   shared:X          mount is shared in peer group X

                   master:X          mount is slave to peer group X

                   propagate_from:X  mount  is  slave and receives propagation
                                     from peer group X (*)

                   unbindable        mount is unbindable

              (*) X is the closest dominant peer  group  under  the  process's
              root.  If X is the immediate master of the mount, or if there is
              no dominant peer group under the same root, then only the  "mas-
              ter:X" field is present and not the "propagate_from:X" field.

              For  more  information  on  mount  propagation  see:  Documenta-
              tion/filesystems/sharedsubtree.txt in the kernel source tree.

       /proc/[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 set-
              ting.  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  dis-
              played  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 pri-
              vate 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 speci-
              fiers, are:

              pid %d      The process ID.

              comm %s     The filename  of  the  executable,  in  parentheses.
                          This  is  visible  whether  or not the executable is
                          swapped out.

              state %c    One character from the string "RSDZTW"  where  R  is
                          running,  S  is sleeping in an interruptible wait, D
                          is waiting in uninterruptible disk sleep, Z is  zom-
                          bie,  T is traced or stopped (on a signal), and W is

              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 con-
                          trolling terminal of the process.

              flags %u (%lu before Linux 2.6.22)
                          The kernel flags word of the process.  For bit mean-
                          ings,  see  the  PF_*  defines  in  <linux/sched.h>.
                          Details depend on the kernel version.

              minflt %lu  The number of minor  faults  the  process  has  made
                          which  have  not required loading a memory page from

              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 chil-
                          dren have been scheduled in user mode,  measured  in
                          clock  ticks  (divide by sysconf(_SC_CLK_TCK).  (See
                          also   times(2).)    This   includes   guest   time,
                          cguest_time  (time  spent running a virtual CPU, see

              cstime %ld  Amount of time that this process's waited-for  chil-
                          dren have been scheduled in kernel mode, measured in
                          clock ticks (divide by sysconf(_SC_CLK_TCK).

              priority %ld
                          (Explanation for Linux 2.6) For processes running  a
                          real-time   scheduling  policy  (policy  below;  see
                          sched_setscheduler(2)), this is the negated schedul-
                          ing  priority,  minus  one; that is, a number in the
                          range -2 to -100, corresponding to real-time priori-
                          ties  1  to  99.  For processes running under a non-
                          real-time scheduling policy, this is  the  raw  nice
                          value (setpriority(2)) as represented in the kernel.
                          The kernel stores nice  values  as  numbers  in  the
                          range  0  (high)  to  39 (low), corresponding to the
                          user-visible nice range of -20 to 19.

                          Before Linux 2.6, this was a scaled value  based  on
                          the scheduler weighting given to this process.

              nice %ld    The  nice value (see setpriority(2)), a value in the
                          range 19 (low priority) to -20 (high priority).

              num_threads %ld
                          Number of threads in this process (since Linux 2.6).
                          Before kernel 2.6, this field was hard coded to 0 as
                          a placeholder for an earlier removed field.

              itrealvalue %ld
                          The time in jiffies before the next SIGALRM is  sent
                          to the process due to an interval timer.  Since ker-
                          nel 2.6.17, this field is no longer maintained,  and
                          is hard coded as 0.

              starttime %llu (was %lu before Linux 2.6)
                          The time in jiffies the process started after system

              vsize %lu   Virtual memory size in bytes.

              rss %ld     Resident Set Size: number of pages the  process  has
                          in  real memory.  This is just the pages which count
                          towards text, data, or stack space.  This  does  not
                          include  pages which have not been demand-loaded in,
                          or which are swapped out.

              rsslim %lu  Current soft limit  in  bytes  on  the  rss  of  the
                          process;  see  the description of RLIMIT_RSS in get-

              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  deci-
                          mal  number.   Obsolete, because it does not provide
                          information on real-time  signals;  use  /proc/[num-
                          ber]/status instead.

              blocked %lu The  bitmap of blocked signals, displayed as a deci-
                          mal number.  Obsolete, because it does  not  provide
                          information  on  real-time  signals; use /proc/[num-
                          ber]/status instead.

              sigignore %lu
                          The bitmap of ignored signals, displayed as a  deci-
                          mal  number.   Obsolete, because it does not provide
                          information on real-time  signals;  use  /proc/[num-
                          ber]/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/[num-
                          ber]/status instead.

              wchan %lu   This is the "channel" in which the process is  wait-
                          ing.  It is the address of a system call, and can be
                          looked up in a namelist if you need a textual  name.
                          (If you have an up-to-date /etc/psdatabase, then try
                          ps -l to see the WCHAN field in action.)

              nswap %lu   Number of pages swapped (not maintained).

              cnswap %lu  Cumulative nswap  for  child  processes  (not  main-

              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 vir-
                          tual  CPU for a guest operating system), measured in
                          clock ticks (divide by sysconf(_SC_CLK_TCK).

              cguest_time %ld (since Linux 2.6.24)
                          Guest time of the process's  children,  measured  in
                          clock ticks (divide by sysconf(_SC_CLK_TCK).

              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 capabili-

              * 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/[num-
              ber]  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/[num-
              ber]/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  configur-
              ing  the  kernel  (using make xconfig, make config, or similar).
              The file contents are compressed;  view  or  search  them  using
              zcat(1), zgrep(1), etc.  As long as no changes have been made to
              the following file, the contents of /proc/config.gz are the same
              as those provided by :

                  cat /lib/modules/$(uname -r)/build/.config

              /proc/config.gz  is  only  provided  if the kernel is configured
              with CONFIG_IKCONFIG_PROC.

              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 dif-
              ferent 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 mes-

              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 sepa-
              rated by a slash (/).  The first of these is the number of  cur-
              rently   executing   kernel   scheduling   entities  (processes,
              threads); this will be less than or equal to the number of CPUs.
              The  value  after  the  slash is the number of kernel scheduling
              entities that currently exist on the system.  The fifth field is
              the  PID  of  the  process that was most recently created on the

              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  open-
              ing  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/Documenta-
              tion/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 struc-
              tures and are, therefore, readable with  cat(1).   However,  the
              standard  netstat(8) suite provides much cleaner access to these

              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 ker-
              nel hash slot for the socket, the "local_address" is  the  local
              address  and  protocol number pair.  "St" is the internal status
              of the socket.  The "tx_queue" and "rx_queue" are  the  outgoing
              and  incoming  data  queue in terms of kernel memory usage.  The
              "tr", "tm->when", and "rexmits" fields are not used by RAW.  The
              "uid"  field  holds  the  effective  UID  of  the creator of the

              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  ker-
              nel  hash  slot for the socket, the "local_address" is the local
              address and port number pair.  The "rem_address" is  the  remote
              address and port number pair (if connected).  "St" is the inter-
              nal status of the socket.  The "tx_queue" and "rx_queue" are the
              outgoing  and  incoming  data  queue  in  terms of kernel memory
              usage.  The "tr", "tm->when", and "rexmits" fields hold internal
              information  of  the kernel socket state and are only useful for
              debugging.  The "uid" field holds the effective UID of the  cre-
              ator of the socket.

              Holds  a  dump of the UDP socket table.  Much of the information
              is not of use apart from debugging.  The "sl" value is the  ker-
              nel  hash  slot for the socket, the "local_address" is the local
              address and port number pair.  The "rem_address" is  the  remote
              address  and port number pair (if connected). "St" is the inter-
              nal status of the socket.  The "tx_queue" and "rx_queue" are the
              outgoing  and  incoming  data  queue  in  terms of kernel memory
              usage.  The "tr", "tm->when", and "rexmits" fields are not  used
              by  UDP.  The "uid" field holds the effective UID of the creator
              of the socket.  The format is:

 sl  local_address rem_address   st tx_queue rx_queue tr rexmits  tm->when uid
  1: 01642C89:0201 0C642C89:03FF 01 00000000:00000001 01:000071BA 00000000 0
  1: 00000000:0801 00000000:0000 0A 00000000:00000000 00:00000000 6F000100 0
  1: 00000000:0201 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0

              Lists the Unix domain sockets  present  within  the  system  and
              their status.  The format is:
              Num RefCount Protocol Flags    Type St Path
               0: 00000002 00000000 00000000 0001 03
               1: 00000001 00000000 00010000 0001 01 /dev/printer

              Here  "Num"  is  the kernel table slot number, "RefCount" is the
              number of users of the socket, "Protocol" is currently always 0,
              "Flags"  represent  the internal kernel flags holding the status
              of the socket.  Currently, type is always "1" (Unix domain data-
              gram  sockets are not yet supported in the kernel).  "St" is the
              internal state of the socket and Path is the bound path (if any)
              of the socket.

              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  ini-
              tialization and their configuration.

              This  file has been deprecated in favor of a new /proc interface
              for PCI  (/proc/bus/pci).   It  became  optional  in  Linux  2.2
              (available  with CONFIG_PCI_OLD_PROC set at kernel compilation).
              It became once more non-optionally enabled in Linux 2.4.   Next,
              it  was  deprecated  in  Linux  2.6  (still  available with CON-
              FIG_PCI_LEGACY_PROC set), and finally removed  altogether  since
              Linux 2.6.17.

              A directory with the scsi mid-level pseudo-file and various SCSI
              low-level driver directories, which contain a file for each SCSI
              host  in  this system, all of which give the status of some part
              of the SCSI IO subsystem.  These files contain ASCII  structures
              and are, therefore, readable with cat(1).

              You  can also write to some of the files to reconfigure the sub-
              system or switch certain features on or off.

              This is a listing of all SCSI devices known to the kernel.   The
              listing  is  similar  to  the one seen during bootup.  scsi cur-
              rently supports only the add-single-device command which  allows
              root to add a hotplugged device to the list of known devices.

              The command

                  echo 'scsi add-single-device 1 0 5 0' > /proc/scsi/scsi

              will  cause host scsi1 to scan on SCSI channel 0 for a device on
              ID 5 LUN 0.  If there is already a device known on this  address
              or the address is invalid, an error will be returned.

              [drivername]  can  currently  be  NCR53c7xx,  aha152x,  aha1542,
              aha1740, aic7xxx, buslogic, eata_dma, eata_pio, fdomain, in2000,
              pas16,  qlogic,  scsi_debug, seagate, t128, u15-24f, ultrastore,
              or wd7000.  These directories show up for all drivers that  reg-
              istered  at  least  one  SCSI HBA.  Every directory contains one
              file per registered host.  Every host-file is  named  after  the
              number the host was assigned during initialization.

              Reading these files will usually show driver and host configura-
              tion, statistics, etc.

              Writing to these files  allows  different  things  on  different
              hosts.   For  example,  with the latency and nolatency commands,
              root can switch on and off command latency measurement  code  in
              the  eata_dma driver.  With the lockup and unlock commands, root
              can control bus lockups simulated by the scsi_debug driver.

              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 operat-
                     ing systems under the control of the Linux kernel.

              page 5741 1808
                     The number of pages the system paged in  and  the  number
                     that were paged out (from disk).

              swap 1 0
                     The  number  of  swap pages that have been brought in and

              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  subdirec-

       /proc/sys/abi (since Linux 2.4.10)
              This  directory may contain files with application binary infor-
              mation.  See the kernel source file Documentation/sysctl/abi.txt
              for more information.

              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 inter-
              face.  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 sig-
              nal to that process notifying it that another process is waiting
              to open the file.  If the lease holder does not remove or  down-
              grade  the  lease  within this grace period, the kernel forcibly
              breaks the lease.

              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  bina-
              ries.  Three different integer values can be specified:

              0 (default)  This  provides  the  traditional (pre-Linux 2.6.13)
              behavior.  A core dump will not be produced for a process  which
              has  changed  credentials  (by calling seteuid(2), setgid(2), or
              similar, or by executing a set-user-ID or set-group-ID  program)
              or whose binary does not have read permission enabled.

              1 ("debug")  All  processes  dump  core when possible.  The core
              dump is owned by the file system user ID of the dumping  process
              and  no security is applied.  This is intended for system debug-
              ging situations only.  Ptrace is unchecked.

              2 ("suidsafe") Any binary which normally  would  not  be  dumped
              (see  "0"  above)  is dumped readable by root only.  This allows
              the user to remove the core dump file but not to read  it.   For
              security  reasons core dumps in this mode will not overwrite one
              another or other files.  This mode is appropriate when  adminis-
              trators  are  attempting  to debug problems in a normal environ-

              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, a described below.

              This file contains three numbers: highwater, lowwater, and  fre-
              quency.  If BSD-style process accounting is enabled these values
              control its behavior.  If free space on file  system  where  the
              log  lives  goes below lowwater percent accounting suspends.  If
              free space gets  above  highwater  percent  accounting  resumes.
              frequency  determines  how often the kernel checks the amount of
              free space (value is in seconds).  Default values are 4,  2  and
              30.   That  is,  suspend accounting if 2% or less space is free;
              resume it if 4% or more  space  is  free;  consider  information
              about amount of free space valid for 30 seconds.

       /proc/sys/kernel/cap-bound (from Linux 2.2 to 2.6.24)
              This  file holds the value of the kernel capability bounding set
              (expressed as a signed  decimal  number).   This  set  is  ANDed
              against   the   capabilities   permitted  to  a  process  during
              execve(2).  Starting with Linux 2.6.25, the system-wide capabil-
              ity  bounding  set disappeared, and was replaced by a per-thread
              bounding set; see capabilities(7).

              See core(5).

              See core(5).

              This file controls the handling of Ctrl-Alt-Del  from  the  key-
              board.   When  the  value  in  this  file  is 0, Ctrl-Alt-Del is
              trapped and sent to the init(8) program  to  handle  a  graceful
              restart.   When the value is greater than zero, Linux's reaction
              to a Vulcan Nerve Pinch (tm) will be an immediate reboot,  with-
              out  even syncing its dirty buffers.  Note: when a program (like
              dosemu) has the keyboard in  "raw"  mode,  the  ctrl-alt-del  is
              intercepted by the program before it ever reaches the kernel tty
              layer, and it's up to the program to decide what to do with it.

              This file contains the path for the hotplug policy  agent.   The
              default value in this file is /sbin/hotplug.

       /proc/sys/kernel/domainname and /proc/sys/kernel/hostname
              can  be  used  to  set the NIS/YP domainname and the hostname of
              your box in exactly the same way as the  commands  domainname(1)
              and hostname(1), that is:

                  # echo "darkstar" > /proc/sys/kernel/hostname
                  # echo "mydomain" > /proc/sys/kernel/domainname

              has the same effect as

                  # hostname "darkstar"
                  # domainname "mydomain"

              Note,  however, that the classic darkstar.frop.org has the host-
              name "darkstar" and DNS (Internet Domain Name Server) domainname
              "frop.org", not to be confused with the NIS (Network Information
              Service) or YP (Yellow  Pages)  domainname.   These  two  domain
              names  are  in general different.  For a detailed discussion see
              the hostname(1) man page.

              (PowerPC only) If this file is set to a non-zero value, the Pow-
              erPC  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 mes-
              sage 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  autore-
              boot  after  this  number of seconds.  When you use the software
              watchdog device driver, the recommended setting is 60.

       /proc/sys/kernel/panic_on_oops (since Linux 2.5.68)
              This file controls the kernel's behavior when an oops or BUG  is
              encountered.   If this file contains 0, then the system tries to
              continue operation.  If it contains 1, then the system delays  a
              few  seconds  (to give klogd time to record the oops output) and
              then panics.  If the /proc/sys/kernel/panic file  is  also  non-
              zero then the machine will be rebooted.

       /proc/sys/kernel/pid_max ( since Linux 2.5.34)
              This  file  specifies the value at which PIDs wrap around (i.e.,
              the value in this file is one greater  than  the  maximum  PID).
              The  default  value  for  this  file, 32768, results in the same
              range of PIDs as on earlier kernels.  On 32-bit platforms, 32768
              is  the  maximum  value for pid_max.  On 64-bit systems, pid_max
              can be set to any value up to 2^22 (PID_MAX_LIMIT, approximately
              4 million).

       /proc/sys/kernel/powersave-nap (PowerPC only)
              This file contains a flag.  If set, Linux-PPC will use the "nap"
              mode of powersaving, otherwise the "doze" mode will be used.

              The four values in this file are console_loglevel,  default_mes-
              sage_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  con-

       /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 cur-
              rently in use.

              This directory contains various parameters controlling the oper-
              ation of the file /dev/random.  See random(4) for further infor-

              This  file  is  documented  in the kernel source file Documenta-

       /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, buf-
              fer and cache management.

       /proc/sys/vm/drop_caches (since Linux 2.6.16)
              Writing to this file causes the kernel  to  drop  clean  caches,
              dentries  and  inodes from memory, causing that memory to become

              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 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/[num-
              ber]/oom_adj),  and  command name.  This is helpful to determine
              why the OOM-killer was invoked and to identify  the  rogue  task
              that caused it.

              If this contains the value zero, this information is suppressed.
              On very large systems with thousands of tasks,  it  may  not  be
              feasible  to  dump  the  memory  state information for each one.
              Such systems should not be forced to incur a performance penalty
              in OOM situations when the information may not be desired.

              If  this  is set to non-zero, this information is shown whenever
              the OOM-killer actually kills a memory-hogging task.

              The default value is 0.

       /proc/sys/vm/oom_kill_allocating_task (since Linux 2.6.24)
              This enables or disables killing the OOM-triggering task in out-
              of-memory situations.

              If  this  is  set  to zero, the OOM-killer will scan through the
              entire tasklist and select a task based on heuristics  to  kill.
              This  normally selects a rogue memory-hogging task that frees up
              a large amount of memory when killed.

              If this is set to non-zero, the OOM-killer simply kills the task
              that  triggered the out-of-memory condition.  This avoids a pos-
              sibly expensive tasklist scan.

              If /proc/sys/vm/panic_on_oom is non-zero,  it  takes  precedence
              over  whatever  value  is used in /proc/sys/vm/oom_kill_allocat-

              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  get-
              ting 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.

       /proc/sys/vm/panic_on_oom (since Linux 2.6.18)
              This enables or disables a kernel panic in an out-of-memory sit-

              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.

              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  (sec-
              onds), and the amount of time spent in idle process (seconds).

              This string identifies the kernel version that is currently run-
              ning.  It  includes  the  contents  of  /proc/sys/kernel/ostype,
              /proc/sys/kernel/osrelease  and  /proc/sys/kernel/version.   For
            Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994

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

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

       Many strings (i.e., the environment and command line) are in the inter-
       nal 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)
       The kernel source files: Documentation/filesystems/proc.txt, Documenta-

       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                             2008-07-15                           PROC(5)