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

NAME

       proc - process information pseudo-file system

DESCRIPTION

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

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

       /proc/[pid]
              There is a numerical subdirectory for each running process; the subdirectory is named by the process ID.  Each such subdirectory
              contains the following pseudo-files and directories.

       /proc/[pid]/auxv (since 2.6.0-test7)
              This  contains  the  contents of the ELF interpreter information passed to the process at exec time.  The format is one unsigned
              long ID plus one unsigned long value for each entry.  The last entry contains two zeros.

       /proc/[pid]/cmdline
              This holds the complete command line for the process, unless the process is a zombie.  In the latter case, there is  nothing  in
              this  file:  that  is, a read on this file will return 0 characters.  The command-line arguments appear in this file as a set of
              strings separated by null bytes ('\0'), with a further null byte after the last string.

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

       /proc/[pid]/cpuset (since kernel 2.6.12)
              See cpuset(7).

       /proc/[pid]/cwd
              This is a symbolic link to the current working directory of the process.  To find out the current working directory  of  process
              20, for instance, you can do this:

                  $ cd /proc/20/cwd; /bin/pwd

              Note that the pwd command is often a shell built-in, and might not work properly.  In bash(1), you may use pwd -P.

              In  a  multithreaded  process,  the  contents  of this symbolic link are not available if the main thread has already terminated
              (typically by calling pthread_exit(3)).

       /proc/[pid]/environ
              This file contains the environment for the process.  The entries are separated by null bytes ('\0'), and there  may  be  a  null
              byte at the end.  Thus, to print out the environment of process 1, you would do:

                  $ (cat /proc/1/environ; echo) | tr '\000' '\n'

       /proc/[pid]/exe
              Under  Linux  2.2 and later, this file is a symbolic link containing the actual pathname of the executed command.  This symbolic
              link can be dereferenced normally; attempting to open it will open the executable.  You can even  type  /proc/[pid]/exe  to  run
              another copy of the same executable as is being run by process [pid].  In a multithreaded process, the contents of this symbolic
              link are not available if the main thread has already terminated (typically by calling pthread_exit(3)).

              Under Linux 2.0 and earlier /proc/[pid]/exe is a pointer to the binary which was executed, and appears as a  symbolic  link.   A
              readlink(2) call on this file under Linux 2.0 returns a string in the format:

                  [device]:inode

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

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

       /proc/[pid]/fd
              This is a subdirectory containing one entry for each file which the process has open, named by its file descriptor, and which is
              a symbolic link to the actual file.  Thus, 0 is standard input, 1 standard output, 2 standard error, etc.

              In  a  multithreaded  process,  the  contents  of  this  directory  are  not available if the main thread has already terminated
              (typically by calling pthread_exit(3)).

              Programs that will take a filename as a command-line argument, but will not take input from standard input  if  no  argument  is
              supplied,  or  that  write  to  a file named as a command-line argument, but will not send their output to standard output if no
              argument is supplied, can nevertheless be made to use standard  input  or  standard  out  using  /proc/[pid]/fd.   For  example,
              assuming that -i is the flag designating an input file and -o is the flag designating an output file:

                  $ foobar -i /proc/self/fd/0 -o /proc/self/fd/1 ...

              and you have a working filter.

              /proc/self/fd/N  is  approximately  the  same  as  /dev/fd/N  in  some  UNIX  and UNIX-like systems.  Most Linux MAKEDEV scripts
              symbolically link /dev/fd to /proc/self/fd, in fact.

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

                  $ foobar -i /dev/stdin -o /dev/stdout ...

       /proc/[pid]/fdinfo/ (since kernel 2.6.22)
              This  is  a  subdirectory  containing  one  entry  for  each file which the process has open, named by its file descriptor.  The
              contents of each file can be read to obtain information about the corresponding file descriptor, for example:

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

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

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

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

       /proc/[pid]/maps
              A file containing the currently mapped memory regions and their access permissions.

              The format is:

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

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

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

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

              Under Linux 2.0 there is no field giving pathname.

       /proc/[pid]/mem
              This file can be used to access the pages of a process's memory through open(2), read(2), and lseek(2).

       /proc/[pid]/mountinfo (since Linux 2.6.26)
              This file contains information about mount points.  It contains lines of the form:

              36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
              (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)

              The numbers in parentheses are labels for the descriptions below:

              (1)  mount ID: unique identifier of the mount (may be reused after umount(2)).

              (2)  parent ID: ID of parent mount (or of self for the top of the mount tree).

              (3)  major:minor: value of st_dev for files on file system (see stat(2)).

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

              (5)  mount point: mount point relative to the process's root.

              (6)  mount options: per-mount options.

              (7)  optional fields: zero or more fields of the form "tag[:value]".

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

              (9)  file system type: name of file system in the form "type[.subtype]".

              (10) mount source: file system-specific information or "none".

              (11) super options: per-super block options.

              Parsers should ignore all unrecognized optional fields.  Currently the possible optional fields are:

                   shared:X          mount is shared in peer group X

                   master:X          mount is slave to peer group X

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

                   unbindable        mount is unbindable

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

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

       /proc/[pid]/mounts (since Linux 2.4.19)
              This is a list of all the file systems currently mounted in  the  process's  mount  namespace.   The  format  of  this  file  is
              documented  in  fstab(5).   Since  kernel version 2.6.15, this file is pollable: after opening the file for reading, a change in
              this file (i.e., a file system mount or unmount) causes select(2) to mark the file  descriptor  as  readable,  and  poll(2)  and
              epoll_wait(2) mark the file as having an error condition.

       /proc/[pid]/mountstats (since Linux 2.6.17)
              This file exports information (statistics, configuration information) about the mount points in the process's name space.  Lines
              in this file have the form:

              device /dev/sda7 mounted on /home with fstype ext3 [statistics]
              (       1      )            ( 2 )             (3 ) (4)

              The fields in each line are:

              (1)  The name of the mounted device (or "nodevice" if there is no corresponding device).

              (2)  The mount point within the file system tree.

              (3)  The file system type.

              (4)  Optional statistics and configuration  information.   Currently  (as  at  Linux  2.6.26),  only  NFS  file  systems  export
                   information via this field.

              This file is only readable by the owner of the process.

       /proc/[pid]/ns/ (since Linux 3.0)
              This  is  a  subdirectory  containing one entry for each namespace that supports being manipulated by setns(2).  For information
              about namespaces, see clone(2).

       /proc/[pid]/ns/ipc (since Linux 3.0)
              Bind mounting this file (see mount(2)) to somewhere else in the filesystem keeps the IPC namespace of the process  specified  by
              pid alive even if all processes currently in the namespace terminate.

              Opening  this file returns a file handle for the IPC namespace of the process specified by pid.  As long as this file descriptor
              remains open, the IPC namespace will remain alive, even if all processes in the namespace terminate.  The file descriptor can be
              passed to setns(2).

       /proc/[pid]/ns/net (since Linux 3.0)
              Bind  mounting this file (see mount(2)) to somewhere else in the filesystem keeps the network namespace of the process specified
              by pid alive even if all processes in the namespace terminate.

              Opening this file returns a file handle for the network namespace of the process  specified  by  pid.   As  long  as  this  file
              descriptor  remains  open,  the network namespace will remain alive, even if all processes in the namespace terminate.  The file
              descriptor can be passed to setns(2).

       /proc/[pid]/ns/uts (since Linux 3.0)
              Bind mounting this file (see mount(2)) to somewhere else in the filesystem keeps the UTS namespace of the process  specified  by
              pid alive even if all processes currently in the namespace terminate.

              Opening  this file returns a file handle for the UTS namespace of the process specified by pid.  As long as this file descriptor
              remains open, the UTS namespace will remain alive, even if all processes in the namespace terminate.  The file descriptor can be
              passed to setns(2).

       /proc/[pid]/numa_maps (since Linux 2.6.14)
              See numa(7).

       /proc/[pid]/oom_adj (since Linux 2.6.11)
              This  file  can  be  used to adjust the score used to select which process should be killed in an out-of-memory (OOM) situation.
              The kernel uses this value for a bit-shift operation of the process's oom_score value: valid values are in the range -16 to +15,
              plus  the  special value -17, which disables OOM-killing altogether for this process.  A positive score increases the likelihood
              of this process being killed by the OOM-killer; a negative score decreases the likelihood.  The default value for this  file  is
              0; a new process inherits its parent's oom_adj setting.  A process must be privileged (CAP_SYS_RESOURCE) to update this file.

       /proc/[pid]/oom_score (since Linux 2.6.11)
              This  file  displays the current score that the kernel gives to this process for the purpose of selecting a process for the OOM-
              killer.  A higher score means that the process is more likely to be selected by the OOM-killer.  The basis for this score is the
              amount of memory used by the process, with increases (+) or decreases (-) for factors including:

              * whether the process creates a lot of children using fork(2) (+);

              * whether the process has been running a long time, or has used a lot of CPU time (-);

              * whether the process has a low nice value (i.e., > 0) (+);

              * whether the process is privileged (-); and

              * whether the process is making direct hardware access (-).

              The oom_score also reflects the bit-shift adjustment specified by the oom_adj setting for the process.

       /proc/[pid]/root
              UNIX  and  Linux  support  the  idea of a per-process root of the file system, set by the chroot(2) system call.  This file is a
              symbolic link that points to the process's root directory, and behaves as exe, fd/*, etc. do.

              In a multithreaded process, the contents of this symbolic link are not available if  the  main  thread  has  already  terminated
              (typically by calling pthread_exit(3)).

       /proc/[pid]/smaps (since Linux 2.6.14)
              This  file shows memory consumption for each of the process's mappings.  For each of mappings there is a series of lines such as
              the following:

                  08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
                  Size:               464 kB
                  Rss:                424 kB
                  Shared_Clean:       424 kB
                  Shared_Dirty:         0 kB
                  Private_Clean:        0 kB
                  Private_Dirty:        0 kB

              The first of these lines shows the same information as is displayed for the mapping in /proc/[pid]/maps.   The  remaining  lines
              show  the size of the mapping, the amount of the mapping that is currently resident in RAM, the number of clean and dirty shared
              pages in the mapping, and the number of clean and dirty private pages in the mapping.

              This file is only present if the CONFIG_MMU kernel configuration option is enabled.

       /proc/[pid]/stat
              Status information about the process.  This is used by ps(1).  It is defined in /usr/src/linux/fs/proc/array.c.

              The fields, in order, with their proper scanf(3) format specifiers, are:

              pid %d      The process ID.

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

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

              ppid %d     The PID of the parent.

              pgrp %d     The process group ID of the process.

              session %d  The session ID of the process.

              tty_nr %d   The  controlling terminal of the process.  (The minor device number is contained in the combination of bits 31 to 20
                          and 7 to 0; the major device number is in bits 15 to 8.)

              tpgid %d    The ID of the foreground process group of the controlling terminal of the process.

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

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

              cminflt %lu The number of minor faults that the process's waited-for children have made.

              majflt %lu  The number of major faults the process has made which have required loading a memory page from disk.

              cmajflt %lu The number of major faults that the process's waited-for children have made.

              utime %lu   Amount  of  time  that  this  process  has  been  scheduled  in  user  mode,  measured  in  clock  ticks  (divide by
                          sysconf(_SC_CLK_TCK).  This includes guest time, guest_time (time spent running a virtual CPU, see below),  so  that
                          applications that are not aware of the guest time field do not lose that time from their calculations.

              stime %lu   Amount  of  time  that  this  process  has  been  scheduled  in  kernel  mode,  measured  in  clock ticks (divide by
                          sysconf(_SC_CLK_TCK).

              cutime %ld  Amount of time that this process's waited-for children have been scheduled in user mode,  measured  in  clock  ticks
                          (divide  by sysconf(_SC_CLK_TCK).  (See also times(2).)  This includes guest time, cguest_time (time spent running a
                          virtual CPU, see below).

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

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

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

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

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

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

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

              vsize %lu   Virtual memory size in bytes.

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

              rsslim %lu  Current soft limit in bytes on the rss of the process; see the description of RLIMIT_RSS in getpriority(2).

              startcode %lu
                          The address above which program text can run.

              endcode %lu The address below which program text can run.

              startstack %lu
                          The address of the start (i.e., bottom) of the stack.

              kstkesp %lu The current value of ESP (stack pointer), as found in the kernel stack page for the process.

              kstkeip %lu The current EIP (instruction pointer).

              signal %lu  The bitmap of pending signals, displayed as a decimal number.  Obsolete, because it does not provide information  on
                          real-time signals; use /proc/[pid]/status instead.

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

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

              sigcatch %lu
                          The  bitmap  of caught signals, displayed as a decimal number.  Obsolete, because it does not provide information on
                          real-time signals; use /proc/[pid]/status instead.

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

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

              cnswap %lu  Cumulative nswap for child processes (not maintained).

              exit_signal %d (since Linux 2.1.22)
                          Signal to be sent to parent when we die.

              processor %d (since Linux 2.2.8)
                          CPU number last executed on.

              rt_priority %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
                          Real-time scheduling priority, a number in the range 1 to 99 for processes scheduled under a real-time policy, or 0,
                          for non-real-time processes (see sched_setscheduler(2)).

              policy %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
                          Scheduling policy (see sched_setscheduler(2)).  Decode using the SCHED_* constants in linux/sched.h.

              delayacct_blkio_ticks %llu (since Linux 2.6.18)
                          Aggregated block I/O delays, measured in clock ticks (centiseconds).

              guest_time %lu (since Linux 2.6.24)
                          Guest  time  of the process (time spent running a virtual CPU for a guest operating system), measured in clock ticks
                          (divide by sysconf(_SC_CLK_TCK).

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

       /proc/[pid]/statm
              Provides information about memory usage, measured in pages.  The columns are:

                  size       total program size
                             (same as VmSize in /proc/[pid]/status)
                  resident   resident set size
                             (same as VmRSS in /proc/[pid]/status)
                  share      shared pages (from shared mappings)
                  text       text (code)
                  lib        library (unused in Linux 2.6)
                  data       data + stack
                  dt         dirty pages (unused in Linux 2.6)

       /proc/[pid]/status
              Provides much of the information in /proc/[pid]/stat and /proc/[pid]/statm in a  format  that's  easier  for  humans  to  parse.
              Here's an example:

                  $ cat /proc/$$/status
                  Name:   bash
                  State:  S (sleeping)
                  Tgid:   3515
                  Pid:    3515
                  PPid:   3452
                  TracerPid:      0
                  Uid:    1000    1000    1000    1000
                  Gid:    100     100     100     100
                  FDSize: 256
                  Groups: 16 33 100
                  VmPeak:     9136 kB
                  VmSize:     7896 kB
                  VmLck:         0 kB
                  VmHWM:      7572 kB
                  VmRSS:      6316 kB
                  VmData:     5224 kB
                  VmStk:        88 kB
                  VmExe:       572 kB
                  VmLib:      1708 kB
                  VmPTE:        20 kB
                  Threads:        1
                  SigQ:   0/3067
                  SigPnd: 0000000000000000
                  ShdPnd: 0000000000000000
                  SigBlk: 0000000000010000
                  SigIgn: 0000000000384004
                  SigCgt: 000000004b813efb
                  CapInh: 0000000000000000
                  CapPrm: 0000000000000000
                  CapEff: 0000000000000000
                  CapBnd: ffffffffffffffff
                  Cpus_allowed:   00000001
                  Cpus_allowed_list:      0
                  Mems_allowed:   1
                  Mems_allowed_list:      0
                  voluntary_ctxt_switches:        150
                  nonvoluntary_ctxt_switches:     545

              The fields are as follows:

              * Name: Command run by this process.

              * State:  Current  state  of  the  process.   One of "R (running)", "S (sleeping)", "D (disk sleep)", "T (stopped)", "T (tracing
                stop)", "Z (zombie)", or "X (dead)".

              * Tgid: Thread group ID (i.e., Process ID).

              * Pid: Thread ID (see gettid(2)).

              * PPid: PID of parent process.

              * TracerPid: PID of process tracing this process (0 if not being traced).

              * Uid, Gid: Real, effective, saved set, and file system UIDs (GIDs).

              * FDSize: Number of file descriptor slots currently allocated.

              * Groups: Supplementary group list.

              * VmPeak: Peak virtual memory size.

              * VmSize: Virtual memory size.

              * VmLck: Locked memory size (see mlock(3)).

              * VmHWM: Peak resident set size ("high water mark").

              * VmRSS: Resident set size.

              * VmData, VmStk, VmExe: Size of data, stack, and text segments.

              * VmLib: Shared library code size.

              * VmPTE: Page table entries size (since Linux 2.6.10).

              * Threads: Number of threads in process containing this thread.

              * SigQ: This field contains two slash-separated numbers that relate to queued signals for the real user ID of this process.  The
                first  of  these  is the number of currently queued signals for this real user ID, and the second is the resource limit on the
                number of queued signals for this process (see the description of RLIMIT_SIGPENDING in getrlimit(2)).

              * SigPnd, ShdPnd: Number of signals pending for thread and for process as a whole (see pthreads(7) and signal(7)).

              * SigBlk, SigIgn, SigCgt: Masks indicating signals being blocked, ignored, and caught (see signal(7)).

              * CapInh, CapPrm, CapEff: Masks of capabilities enabled in inheritable, permitted, and effective sets (see capabilities(7)).

              * CapBnd: Capability Bounding set (since kernel 2.6.26, see capabilities(7)).

              * Cpus_allowed: Mask of CPUs on which this process may run (since Linux 2.6.24, see cpuset(7)).

              * Cpus_allowed_list: Same as previous, but in "list format" (since Linux 2.6.26, see cpuset(7)).

              * Mems_allowed: Mask of memory nodes allowed to this process (since Linux 2.6.24, see cpuset(7)).

              * Mems_allowed_list: Same as previous, but in "list format" (since Linux 2.6.26, see cpuset(7)).

              * voluntary_context_switches, nonvoluntary_context_switches: Number of voluntary and involuntary context switches  (since  Linux
                2.6.23).

       /proc/[pid]/task (since Linux 2.6.0-test6)
              This  is  a  directory  that  contains  one  subdirectory  for each thread in the process.  The name of each subdirectory is the
              numerical thread ID ([tid]) of the thread (see gettid(2)).  Within each of these subdirectories, there is a set  of  files  with
              the  same  names and contents as under the /proc/[pid] directories.  For attributes that are shared by all threads, the contents
              for each of the files under the task/[tid] subdirectories will  be  the  same  as  in  the  corresponding  file  in  the  parent
              /proc/[pid]  directory  (e.g.,  in  a  multithreaded  process,  all  of the task/[tid]/cwd files will have the same value as the
              /proc/[pid]/cwd file in the parent directory, since all of the threads in a process share a working directory).  For  attributes
              that  are  distinct for each thread, the corresponding files under task/[tid] may have different values (e.g., various fields in
              each of the task/[tid]/status files may be different for each thread).

              In a multithreaded process, the contents of the /proc/[pid]/task directory are not available if  the  main  thread  has  already
              terminated (typically by calling pthread_exit(3)).

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

       /proc/bus
              Contains subdirectories for installed busses.

       /proc/bus/pccard
              Subdirectory for PCMCIA devices when CONFIG_PCMCIA is set at kernel compilation time.

       /proc/bus/pccard/drivers

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

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

       /proc/cmdline
              Arguments passed to the Linux kernel at boot time.  Often done via a boot manager such as lilo(8) or grub(8).

       /proc/config.gz (since Linux 2.6)
              This file exposes the configuration options that were used to build the currently running kernel, in the  same  format  as  they
              would be shown in the .config file that resulted when configuring the kernel (using make xconfig, make config, or similar).  The
              file contents are compressed; view or search them using zcat(1), zgrep(1), etc.  As long as no changes have  been  made  to  the
              following file, the contents of /proc/config.gz are the same as those provided by :

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

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

       /proc/cpuinfo
              This  is  a  collection  of  CPU and system architecture dependent items, for each supported architecture a different list.  Two
              common entries are processor which gives  CPU  number  and  bogomips;  a  system  constant  that  is  calculated  during  kernel
              initialization.  SMP machines have information for each CPU.

       /proc/devices
              Text listing of major numbers and device groups.  This can be used by MAKEDEV scripts for consistency with the kernel.

       /proc/diskstats (since Linux 2.5.69)
              This  file  contains disk I/O statistics for each disk device.  See the kernel source file Documentation/iostats.txt for further
              information.

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

       /proc/driver
              Empty subdirectory.

       /proc/execdomains
              List of the execution domains (ABI personalities).

       /proc/fb
              Frame buffer information when CONFIG_FB is defined during kernel compilation.

       /proc/filesystems
              A text listing of the file systems which are supported by the kernel, namely file systems which were compiled into the kernel or
              whose kernel modules are currently loaded.  (See also filesystems(5).)  If a file system is marked with "nodev", this means that
              it does not require a block device to be mounted (e.g., virtual file system, network file system).

              Incidentally, this file may be used by mount(8) when no file system is specified and it didn't  manage  to  determine  the  file
              system type.  Then file systems contained in this file are tried (excepted those that are marked with "nodev").

       /proc/fs
              Empty subdirectory.

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

                  cache              buffer size in KB
                  capacity           number of sectors
                  driver             driver version
                  geometry           physical and logical geometry
                  identify           in hexadecimal
                  media              media type
                  model              manufacturer's model number
                  settings           drive settings
                  smart_thresholds   in hexadecimal
                  smart_values       in hexadecimal

              The hdparm(8) utility provides access to this information in a friendly format.

       /proc/interrupts
              This is used to record the number of interrupts  per  CPU  per  IO  device.   Since  Linux  2.6.24,  for  the  i386  and  x86_64
              architectures,  at  least, this also includes interrupts internal to the system (that is, not associated with a device as such),
              such as NMI (nonmaskable interrupt), LOC (local  timer  interrupt),  and  for  SMP  systems,  TLB  (TLB  flush  interrupt),  RES
              (rescheduling  interrupt),  CAL  (remote  function  call interrupt), and possibly others.  Very easy to read formatting, done in
              ASCII.

       /proc/iomem
              I/O memory map in Linux 2.4.

       /proc/ioports
              This is a list of currently registered Input-Output port regions that are in use.

       /proc/kallsyms (since Linux 2.5.71)
              This holds the kernel exported symbol definitions used by the modules(X) tools to dynamically link and  bind  loadable  modules.
              In Linux 2.5.47 and earlier, a similar file with slightly different syntax was named ksyms.

       /proc/kcore
              This file represents the physical memory of the system and is stored in the ELF core file format.  With this pseudo-file, and an
              unstripped kernel (/usr/src/linux/vmlinux) binary, GDB can be used to examine the current state of any kernel data structures.

              The total length of the file is the size of physical memory (RAM) plus 4KB.

       /proc/kmsg
              This file can be used instead of the syslog(2) system call to read kernel messages.  A process must have superuser privileges to
              read  this  file, and only one process should read this file.  This file should not be read if a syslog process is running which
              uses the syslog(2) system call facility to log kernel messages.

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

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

       /proc/loadavg
              The first three fields in this file are load average figures giving the number of jobs in the run queue (state R) or waiting for
              disk  I/O  (state  D)  averaged over 1, 5, and 15 minutes.  They are the same as the load average numbers given by uptime(1) and
              other programs.  The fourth field consists of two numbers separated by a slash (/).   The  first  of  these  is  the  number  of
              currently executing kernel scheduling entities (processes, threads); this will be less than or equal to the number of CPUs.  The
              value after the slash is the number of kernel scheduling entities that currently exist on the system.  The fifth  field  is  the
              PID of the process that was most recently created on the system.

       /proc/locks
              This file shows current file locks (flock(2) and fcntl(2)) and leases (fcntl(2)).

       /proc/malloc (only up to and including Linux 2.2)
              This file is only present if CONFIG_DEBUG_MALLOC was defined during compilation.

       /proc/meminfo
              This  file  reports  statistics  about  memory usage on the system.  It is used by free(1) to report the amount of free and used
              memory (both physical and swap) on the system as well as the shared memory and buffers used by the kernel.

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

       /proc/mounts
              Before kernel 2.4.19, this file was a list of all the file systems currently mounted on the system.  With  the  introduction  of
              per-process  mount namespaces in Linux 2.4.19, this file became a link to /proc/self/mounts, which lists the mount points of the
              process's own mount namespace.  The format of this file is documented in fstab(5).

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

       /proc/net
              various net pseudo-files, all of which give the status of some  part  of  the  networking  layer.   These  files  contain  ASCII
              structures  and  are,  therefore,  readable with cat(1).  However, the standard netstat(8) suite provides much cleaner access to
              these files.

       /proc/net/arp
              This holds an ASCII readable dump of the kernel ARP table used for address resolutions.  It will show both  dynamically  learned
              and preprogrammed ARP entries.  The format is:

        IP address     HW type   Flags     HW address          Mask   Device
        192.168.0.50   0x1       0x2       00:50:BF:25:68:F3   *      eth0
        192.168.0.250  0x1       0xc       00:00:00:00:00:00   *      eth0

              Here  "IP  address"  is the IPv4 address of the machine and the "HW type" is the hardware type of the address from RFC 826.  The
              flags are the internal flags of the ARP structure (as defined in /usr/include/linux/if_arp.h) and the "HW address" is  the  data
              link layer mapping for that IP address if it is known.

       /proc/net/dev
              The  dev pseudo-file contains network device status information.  This gives the number of received and sent packets, the number
              of errors and collisions and other basic statistics.  These are used by the ifconfig(8) program to report  device  status.   The
              format is:

 Inter-|   Receive                                                |  Transmit
  face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
     lo: 2776770   11307    0    0    0     0          0         0  2776770   11307    0    0    0     0       0          0
   eth0: 1215645    2751    0    0    0     0          0         0  1782404    4324    0    0    0   427       0          0
   ppp0: 1622270    5552    1    0    0     0          0         0   354130    5669    0    0    0     0       0          0
   tap0:    7714      81    0    0    0     0          0         0     7714      81    0    0    0     0       0          0

       /proc/net/dev_mcast
              Defined in /usr/src/linux/net/core/dev_mcast.c:
                   indx interface_name  dmi_u dmi_g dmi_address
                   2    eth0            1     0     01005e000001
                   3    eth1            1     0     01005e000001
                   4    eth2            1     0     01005e000001

       /proc/net/igmp
              Internet Group Management Protocol.  Defined in /usr/src/linux/net/core/igmp.c.

       /proc/net/rarp
              This file uses the same format as the arp file and contains the current reverse mapping database used to provide rarp(8) reverse
              address lookup services.  If RARP is not configured into the kernel, this file will not be present.

       /proc/net/raw
              Holds a dump of the RAW socket table.  Much of the information is not of use apart from debugging.  The "sl" value is the kernel
              hash slot for the socket, the "local_address" is the local address and protocol number pair.  "St" is the internal status of the
              socket.  The "tx_queue" and "rx_queue" are the outgoing and incoming data queue in terms of  kernel  memory  usage.   The  "tr",
              "tm->when", and "rexmits" fields are not used by RAW.  The "uid" field holds the effective UID of the creator of the socket.

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

       /proc/net/tcp
              Holds a dump of the TCP socket table.  Much of the information is not of use apart from debugging.  The "sl" value is the kernel
              hash slot for the socket, the "local_address" is the local address and port  number  pair.   The  "rem_address"  is  the  remote
              address  and port number pair (if connected).  "St" is the internal status of the socket.  The "tx_queue" and "rx_queue" are the
              outgoing and incoming data queue in terms of kernel memory usage.  The "tr", "tm->when",  and  "rexmits"  fields  hold  internal
              information  of  the  kernel  socket  state  and  are only useful for debugging.  The "uid" field holds the effective UID of the
              creator of the socket.

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

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

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

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

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

       /proc/pci
              This is a listing of all PCI devices found during kernel initialization and their configuration.

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

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

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

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

              The command

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

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

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

              Reading these files will usually show driver and host configuration, statistics, etc.

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

       /proc/self
              This  directory  refers  to  the  process  accessing the /proc file system, and is identical to the /proc directory named by the
              process ID of the same process.

       /proc/slabinfo
              Information about kernel caches.  Since Linux 2.6.16 this file is only present if the CONFIG_SLAB kernel configuration option is
              enabled.  The columns in /proc/slabinfo are:

                  cache-name
                  num-active-objs
                  total-objs
                  object-size
                  num-active-slabs
                  total-slabs
                  num-pages-per-slab

              See slabinfo(5) for details.

       /proc/stat
              kernel/system statistics.  Varies with architecture.  Common entries include:

              cpu  3357 0 4313 1362393
                     The amount of time, measured in units of USER_HZ (1/100ths of a second on most architectures, use sysconf(_SC_CLK_TCK) to
                     obtain the right value), that the system spent in user mode, user mode with low priority (nice),  system  mode,  and  the
                     idle task, respectively.  The last value should be USER_HZ times the second entry in the uptime pseudo-file.

                     In Linux 2.6 this line includes three additional columns: iowait - time waiting for I/O to complete (since 2.5.41); irq -
                     time servicing interrupts (since 2.6.0-test4); softirq - time servicing softirqs (since 2.6.0-test4).

                     Since Linux 2.6.11, there is an eighth column, steal - stolen time, which is the time spent in  other  operating  systems
                     when running in a virtualized environment

                     Since  Linux  2.6.24,  there  is a ninth column, guest, which is the time spent running a virtual CPU for guest operating
                     systems under the control of the Linux kernel.

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

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

              intr 1462898
                     This line shows counts of interrupts serviced since boot time, for each of the possible  system  interrupts.   The  first
                     column is the total of all interrupts serviced; each subsequent column is the total for a particular interrupt.

              disk_io: (2,0):(31,30,5764,1,2) (3,0):...
                     (major,disk_idx):(noinfo, read_io_ops, blks_read, write_io_ops, blks_written)
                     (Linux 2.4 only)

              ctxt 115315
                     The number of context switches that the system underwent.

              btime 769041601
                     boot time, in seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

              processes 86031
                     Number of forks since boot.

              procs_running 6
                     Number of processes in runnable state.  (Linux 2.5.45 onward.)

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

       /proc/swaps
              Swap areas in use.  See also swapon(8).

       /proc/sys
              This  directory  (present  since 1.3.57) contains a number of files and subdirectories corresponding to kernel variables.  These
              variables can be read and sometimes modified using the /proc file system, and the (deprecated) sysctl(2) system call.

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

       /proc/sys/debug
              This directory may be empty.

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

       /proc/sys/fs
              This directory contains the files and subdirectories for kernel variables related to file systems.

       /proc/sys/fs/binfmt_misc
              Documentation for files in this directory can be found in the kernel sources in Documentation/binfmt_misc.txt.

       /proc/sys/fs/dentry-state (since Linux 2.2)
              This  file  contains  information  about  the status of the directory cache (dcache).  The file contains six numbers, nr_dentry,
              nr_unused, age_limit (age in seconds), want_pages (pages requested by system) and two dummy values.

              * nr_dentry is the number of allocated dentries (dcache entries).  This field is unused in Linux 2.2.

              * nr_unused is the number of unused dentries.

              * age_limit is the age in seconds after which dcache entries can be reclaimed when memory is short.

              * want_pages is nonzero when the kernel has called shrink_dcache_pages() and the dcache isn't pruned yet.

       /proc/sys/fs/dir-notify-enable
              This file can be used to disable or enable the dnotify interface described in fcntl(2) on a system-wide basis.  A value of 0  in
              this file disables the interface, and a value of 1 enables it.

       /proc/sys/fs/dquot-max
              This  file  shows  the maximum number of cached disk quota entries.  On some (2.4) systems, it is not present.  If the number of
              free cached disk quota entries is very low and you have some awesome number of simultaneous system  users,  you  might  want  to
              raise the limit.

       /proc/sys/fs/dquot-nr
              This file shows the number of allocated disk quota entries and the number of free disk quota entries.

       /proc/sys/fs/epoll (since Linux 2.6.28)
              This  directory contains the file max_user_watches, which can be used to limit the amount of kernel memory consumed by the epoll
              interface.  For further details, see epoll(7).

       /proc/sys/fs/file-max
              This file defines a system-wide limit on the number of open files for all processes.  (See also setrlimit(2), which can be  used
              by  a  process  to  set  the  per-process  limit,  RLIMIT_NOFILE, on the number of files it may open.)  If you get lots of error
              messages about running out of file handles, try increasing this value:

              echo 100000 > /proc/sys/fs/file-max

              The kernel constant NR_OPEN imposes an upper limit on the value that may be placed in file-max.

              If  you  increase  /proc/sys/fs/file-max,  be  sure  to  increase  /proc/sys/fs/inode-max  to  3-4  times  the  new   value   of
              /proc/sys/fs/file-max, or you will run out of inodes.

       /proc/sys/fs/file-nr
              This  (read-only)  file  gives  the  number  of files presently opened.  It contains three numbers: the number of allocated file
              handles; the number of free file handles;  and  the  maximum  number  of  file  handles.   The  kernel  allocates  file  handles
              dynamically,  but  it  doesn't  free  them again.  If the number of allocated files is close to the maximum, you should consider
              increasing the maximum.  When the number of free file handles is large, you've encountered a peak in your usage of file  handles
              and you probably don't need to increase the maximum.

       /proc/sys/fs/inode-max
              This  file contains the maximum number of in-memory inodes.  On some (2.4) systems, it may not be present.  This value should be
              3-4 times larger than the value in file-max, since stdin, stdout and network sockets also need an inode to  handle  them.   When
              you regularly run out of inodes, you need to increase this value.

       /proc/sys/fs/inode-nr
              This file contains the first two values from inode-state.

       /proc/sys/fs/inode-state
              This  file  contains  seven  numbers:  nr_inodes,  nr_free_inodes, preshrink, and four dummy values.  nr_inodes is the number of
              inodes the system has allocated.  This can be slightly more than inode-max because Linux allocates them one page full at a time.
              nr_free_inodes  represents  the number of free inodes.  preshrink is nonzero when the nr_inodes > inode-max and the system needs
              to prune the inode list instead of allocating more.

       /proc/sys/fs/inotify (since Linux 2.6.13)
              This directory contains files max_queued_events, max_user_instances, and max_user_watches, that can be used to limit the  amount
              of kernel memory consumed by the inotify interface.  For further details, see inotify(7).

       /proc/sys/fs/lease-break-time
              This  file  specifies  the  grace period that the kernel grants to a process holding a file lease (fcntl(2)) after it has sent a
              signal to that process notifying it that another process is waiting to open the file.  If the lease holder does  not  remove  or
              downgrade the lease within this grace period, the kernel forcibly breaks the lease.

       /proc/sys/fs/leases-enable
              This  file  can  be used to enable or disable file leases (fcntl(2)) on a system-wide basis.  If this file contains the value 0,
              leases are disabled.  A nonzero value enables leases.

       /proc/sys/fs/mqueue (since Linux 2.6.6)
              This directory contains files msg_max, msgsize_max, and queues_max, controlling the resources used by POSIX message queues.  See
              mq_overview(7) for details.

       /proc/sys/fs/overflowgid and /proc/sys/fs/overflowuid
              These  files  allow  you  to  change  the value of the fixed UID and GID.  The default is 65534.  Some file systems only support
              16-bit UIDs and GIDs, although in Linux UIDs and GIDs are 32 bits.  When one of  these  file  systems  is  mounted  with  writes
              enabled, any UID or GID that would exceed 65535 is translated to the overflow value before being written to disk.

       /proc/sys/fs/pipe-max-size (since Linux 2.6.35)
              The  value  in  this  file  defines an upper limit for raising the capacity of a pipe using the fcntl(2) F_SETPIPE_SZ operation.
              This limit applies only to unprivileged processes.  The default value for this file is 1,048,576.  The value  assigned  to  this
              file may be rounded upward, to reflect the value actually employed for a convenient implementation.  To determine the rounded-up
              value, display the contents of this file after assigning a value to it.  The minimum value that can be assigned to this file  is
              the system page size.

       /proc/sys/fs/suid_dumpable (since Linux 2.6.13)
              The  value in this file determines whether core dump files are produced for set-user-ID or otherwise protected/tainted binaries.
              Three different integer values can be specified:

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

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

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

       /proc/sys/fs/super-max
              This  file  controls the maximum number of superblocks, and thus the maximum number of mounted file systems the kernel can have.
              You only need to increase super-max if you need to mount more file systems than the current value in super-max allows you to.

       /proc/sys/fs/super-nr
              This file contains the number of file systems currently mounted.

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

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

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

       /proc/sys/kernel/core_pattern
              See core(5).

       /proc/sys/kernel/core_uses_pid
              See core(5).

       /proc/sys/kernel/ctrl-alt-del
              This file controls the handling of Ctrl-Alt-Del from the keyboard.  When the value in this file is 0,  Ctrl-Alt-Del  is  trapped
              and sent to the init(8) program to handle a graceful restart.  When the value is greater than zero, Linux's reaction to a Vulcan
              Nerve Pinch (tm) will be an immediate reboot, without even syncing its dirty buffers.  Note: when a program  (like  dosemu)  has
              the keyboard in "raw" mode, the ctrl-alt-del is intercepted by the program before it ever reaches the kernel tty layer, and it's
              up to the program to decide what to do with it.

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

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

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

              has the same effect as

                  # hostname 'darkstar'
                  # domainname 'mydomain'

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

       /proc/sys/kernel/htab-reclaim
              (PowerPC  only) If this file is set to a nonzero value, the PowerPC htab (see kernel file Documentation/powerpc/ppc_htab.txt) is
              pruned each time the system hits the idle loop.

       /proc/sys/kernel/l2cr
              (PowerPC only) This file contains a flag that controls the L2 cache of G3 processor  boards.   If  0,  the  cache  is  disabled.
              Enabled if nonzero.

       /proc/sys/kernel/modprobe
              This file contains the path for the kernel module loader.  The default value is /sbin/modprobe.  The file is only present if the
              kernel is built with the CONFIG_KMOD option enabled.  It is described by the kernel  source  file  Documentation/kmod.txt  (only
              present in kernel 2.4 and earlier).

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

       /proc/sys/kernel/msgmni
              This file defines the system-wide limit on the number of message queue identifiers.  (This file is only  present  in  Linux  2.4
              onward.)

       /proc/sys/kernel/msgmnb
              This  file  defines  a  system-wide parameter used to initialize the msg_qbytes setting for subsequently created message queues.
              The msg_qbytes setting specifies the maximum number of bytes that may be written to the message queue.

       /proc/sys/kernel/ostype and /proc/sys/kernel/osrelease
              These files give substrings of /proc/version.

       /proc/sys/kernel/overflowgid and /proc/sys/kernel/overflowuid
              These files duplicate the files /proc/sys/fs/overflowgid and /proc/sys/fs/overflowuid.

       /proc/sys/kernel/panic
              This file gives read/write access to the kernel variable panic_timeout.  If this is zero, the kernel will loop on  a  panic;  if
              nonzero  it indicates that the kernel should autoreboot after this number of seconds.  When you use the software watchdog device
              driver, the recommended setting is 60.

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

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

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

       /proc/sys/kernel/printk
              The    four    values    in    this    file   are   console_loglevel,   default_message_loglevel,   minimum_console_level,   and
              default_console_loglevel.  These values influence printk() behavior when printing or logging error messages.  See syslog(2)  for
              more  info  on  the  different loglevels.  Messages with a higher priority than console_loglevel will be printed to the console.
              Messages without an explicit priority will be printed with  priority  default_message_level.   minimum_console_loglevel  is  the
              minimum   (highest)   value  to  which  console_loglevel  can  be  set.   default_console_loglevel  is  the  default  value  for
              console_loglevel.

       /proc/sys/kernel/pty (since Linux 2.6.4)
              This directory contains two files relating to the number of UNIX 98 pseudoterminals (see pts(4)) on the system.

       /proc/sys/kernel/pty/max
              This file defines the maximum number of pseudoterminals.

       /proc/sys/kernel/pty/nr
              This read-only file indicates how many pseudoterminals are currently in use.

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

       /proc/sys/kernel/real-root-dev
              This file is documented in the kernel source file Documentation/initrd.txt.

       /proc/sys/kernel/reboot-cmd (Sparc only)
              This  file  seems  to  be  a  way  to  give  an  argument to the SPARC ROM/Flash boot loader.  Maybe to tell it what to do after
              rebooting?

       /proc/sys/kernel/rtsig-max
              (Only in kernels up to and including 2.6.7; see setrlimit(2)) This file can be used to tune the maximum number  of  POSIX  real-
              time (queued) signals that can be outstanding in the system.

       /proc/sys/kernel/rtsig-nr
              (Only in kernels up to and including 2.6.7.)  This file shows the number POSIX real-time signals currently queued.

       /proc/sys/kernel/sem (since Linux 2.4)
              This file contains 4 numbers defining limits for System V IPC semaphores.  These fields are, in order:

              SEMMSL  The maximum semaphores per semaphore set.

              SEMMNS  A system-wide limit on the number of semaphores in all semaphore sets.

              SEMOPM  The maximum number of operations that may be specified in a semop(2) call.

              SEMMNI  A system-wide limit on the maximum number of semaphore identifiers.

       /proc/sys/kernel/sg-big-buff
              This file shows the size of the generic SCSI device (sg) buffer.  You can't tune it just yet, but you could change it at compile
              time by editing include/scsi/sg.h and changing the value of SG_BIG_BUFF.  However, there shouldn't be any reason to change  this
              value.

       /proc/sys/kernel/shmall
              This file contains the system-wide limit on the total number of pages of System V shared memory.

       /proc/sys/kernel/shmmax
              This  file  can be used to query and set the run-time limit on the maximum (System V IPC) shared memory segment size that can be
              created.  Shared memory segments up to 1GB are now supported in the kernel.  This value defaults to SHMMAX.

       /proc/sys/kernel/shmmni
              (available in Linux 2.4 and onward) This file specifies the system-wide maximum number of System V shared memory  segments  that
              can be created.

       /proc/sys/kernel/sysrq
              This  file  controls  the  functions allowed to be invoked by the SysRq key.  By default, the file contains 1 meaning that every
              possible SysRq request is allowed (in older  kernel  versions,  SysRq  was  disabled  by  default,  and  you  were  required  to
              specifically enable it at run-time, but this is not the case any more).  Possible values in this file are:

                 0 - disable sysrq completely
                 1 - enable all functions of sysrq
                >1 - bitmask of allowed sysrq functions, as follows:
                        2 - enable control of console logging level
                        4 - enable control of keyboard (SAK, unraw)
                        8 - enable debugging dumps of processes etc.
                       16 - enable sync command
                       32 - enable remount read-only
                       64 - enable signalling of processes (term, kill, oom-kill)
                      128 - allow reboot/poweroff
                      256 - allow nicing of all real-time tasks

              This  file is only present if the CONFIG_MAGIC_SYSRQ kernel configuration option is enabled.  For further details see the kernel
              source file Documentation/sysrq.txt.

       /proc/sys/kernel/version
              This file contains a string like:

                  #5 Wed Feb 25 21:49:24 MET 1998

              The "#5" means that this is the fifth kernel built from this source base and the date behind it indicates the  time  the  kernel
              was built.

       /proc/sys/kernel/threads-max (since Linux 2.3.11)
              This file specifies the system-wide limit on the number of threads (tasks) that can be created on the system.

       /proc/sys/kernel/zero-paged (PowerPC only)
              This  file  contains  a  flag.   When  enabled  (nonzero),  Linux-PPC will pre-zero pages in the idle loop, possibly speeding up
              get_free_pages.

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

       /proc/sys/net/core/somaxconn
              This file defines a ceiling value for the backlog argument of listen(2); see the listen(2) manual page for details.

       /proc/sys/proc
              This directory may be empty.

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

       /proc/sys/vm
              This directory contains files for memory management tuning, buffer and cache management.

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

              To free pagecache, use echo 1 > /proc/sys/vm/drop_caches; to free dentries and inodes, use echo 2 > /proc/sys/vm/drop_caches; to
              free pagecache, dentries and inodes, use echo 3 > /proc/sys/vm/drop_caches.

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

       /proc/sys/vm/legacy_va_layout (since Linux 2.6.9)
              If nonzero, this disables the new 32-bit memory-mapping layout; the kernel will use the legacy (2.4) layout for all processes.

       /proc/sys/vm/memory_failure_early_kill (since Linux 2.6.32)
              Control  how  to  kill  processes  when  an uncorrected memory error (typically a 2-bit error in a memory module) that cannot be
              handled by the kernel is detected in the background by hardware.  In some cases (like the page still  having  a  valid  copy  on
              disk), the kernel will handle the failure transparently without affecting any applications.  But if there is no other up-to-date
              copy of the data, it will kill processes to prevent any data corruptions from propagating.

              The file has one of the following values:

              1:  Kill all processes that have the corrupted-and-not-reloadable page mapped as soon as the corruption is detected.  Note  this
                  is  not  supported  for  a  few  types  of pages, like kernel internally allocated data or the swap cache, but works for the
                  majority of user pages.

              0:  Only unmap the corrupted page from all processes and only kill a process who tries to access it.

              The kill is performed using a SIGBUS signal with si_code set to BUS_MCEERR_AO.  Processes can handle this if they want  to;  see
              sigaction(2) for more details.

              This  feature  is  only  active  on  architectures/platforms  with  advanced  machine check handling and depends on the hardware
              capabilities.

              Applications can override the memory_failure_early_kill setting individually with the prctl(2) PR_MCE_KILL operation.

              Only present if the kernel was configured with CONFIG_MEMORY_FAILURE.

       /proc/sys/vm/memory_failure_recovery (since Linux 2.6.32)
              Enable memory failure recovery (when supported by the platform)

              1:  Attempt recovery.

              0:  Always panic on a memory failure.

              Only present if the kernel was configured with CONFIG_MEMORY_FAILURE.

       /proc/sys/vm/oom_dump_tasks (since Linux 2.6.25)
              Enables a system-wide task dump (excluding kernel threads) to be produced when the kernel performs  an  OOM-killing.   The  dump
              includes  the  following  information  for  each  task (thread, process): thread ID, real user ID, thread group ID (process ID),
              virtual memory size, resident set size, the CPU  that  the  task  is  scheduled  on,  oom_adj  score  (see  the  description  of
              /proc/[pid]/oom_adj),  and  command name.  This is helpful to determine why the OOM-killer was invoked and to identify the rogue
              task that caused it.

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

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

              The default value is 0.

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

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

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

              If    /proc/sys/vm/panic_on_oom    is    nonzero,    it    takes    precedence    over    whatever    value    is    used     in
              /proc/sys/vm/oom_kill_allocating_task.

              The default value is 0.

       /proc/sys/vm/overcommit_memory
              This file contains the kernel virtual memory accounting mode.  Values are:

                     0: heuristic overcommit (this is the default)
                     1: always overcommit, never check
                     2: always check, never overcommit

              In  mode  0,  calls  of  mmap(2)  with MAP_NORESERVE are not checked, and the default check is very weak, leading to the risk of
              getting a process "OOM-killed".  Under Linux 2.4 any nonzero value implies mode 1.  In mode 2 (available since Linux  2.6),  the
              total  virtual  address space on the system is limited to (SS + RAM*(r/100)), where SS is the size of the swap space, and RAM is
              the size of the physical memory, and r is the contents of the file /proc/sys/vm/overcommit_ratio.

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

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

              If this file is set to the value 0, the kernel's OOM-killer will kill some rogue process.  Usually, the OOM-killer  is  able  to
              kill a rogue process and the system will survive.

              If  this  file  is set to the value 1, then the kernel normally panics when out-of-memory happens.  However, if a process limits
              allocations to certain nodes using memory policies (mbind(2) MPOL_BIND) or cpusets (cpuset(7))  and  those  nodes  reach  memory
              exhaustion  status,  one process may be killed by the OOM-killer.  No panic occurs in this case: because other nodes' memory may
              be free, this means the system as a whole may not have reached an out-of-memory situation yet.

              If this file is set to the value 2, the kernel always panics when an out-of-memory condition occurs.

              The default value is 0.  1 and 2 are for failover of clustering.  Select either according to your policy of failover.

       /proc/sys/vm/swappiness
              The value in this file controls how aggressively the kernel will swap memory  pages.   Higher  values  increase  aggressiveness,
              lower values decrease aggressiveness.  The default value is 60.

       /proc/sysrq-trigger (since Linux 2.4.21)
              Writing  a  character  to  this  file  triggers  the same SysRq function as typing ALT-SysRq-<character> (see the description of
              /proc/sys/kernel/sysrq).  This file is normally only writable  by  root.   For  further  details  see  the  kernel  source  file
              Documentation/sysrq.txt.

       /proc/sysvipc
              Subdirectory  containing  the  pseudo-files  msg,  sem  and shm.  These files list the System V Interprocess Communication (IPC)
              objects (respectively: message queues, semaphores, and shared memory) that currently exist  on  the  system,  providing  similar
              information  to  that  available  via  ipcs(1).   These  files have headers and are formatted (one IPC object per line) for easy
              understanding.  svipc(7) provides further background on the information shown by these files.

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

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

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

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

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

NOTES

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

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

SEE ALSO

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

COLOPHON

       This page is part of release 3.35 of the Linux man-pages project.  A description of the project, and information about reporting  bugs,
       can be found at http://man7.org/linux/man-pages/.
 

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