proc(5)



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

NAME
       proc - process information pseudo-filesystem

DESCRIPTION
       The  proc filesystem is a pseudo-filesystem which provides 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  list  describes many of the files and directories under
       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.  See also getauxval(3).

       /proc/[pid]/cgroup (since Linux 2.6.24)
              This  file  describes  control  groups to which the process/task
              belongs.  For each cgroup hierarchy there is one entry  contain-
              ing colon-separated fields of the form:

                  5:cpuacct,cpu,cpuset:/daemons

              The colon-separated fields are, from left to right:

                  1. hierarchy ID number

                  2. set of subsystems bound to the hierarchy

                  3. control  group  in  the  hierarchy  to  which the process
                     belongs

              This file is present only if the CONFIG_CGROUPS kernel  configu-
              ration option is enabled.

       /proc/[pid]/clear_refs (since Linux 2.6.22)

              This  is  a  write-only  file,  writable  only  by  owner of the
              process.

              The following values may be written to the file:

              1 (since Linux 2.6.22)
                     Reset the PG_Referenced and ACCESSED/YOUNG bits  for  all
                     the  pages  associated  with the process.  (Before kernel
                     2.6.32, writing any nonzero value to this file  had  this
                     effect.)

              2 (since Linux 2.6.32)
                     Reset  the  PG_Referenced and ACCESSED/YOUNG bits for all
                     anonymous pages associated with the process.

              3 (since Linux 2.6.32)
                     Reset the PG_Referenced and ACCESSED/YOUNG bits  for  all
                     file-mapped pages associated with the process.

              Clearing  the  PG_Referenced  and ACCESSED/YOUNG bits provides a
              method to measure approximately how much  memory  a  process  is
              using.  One first inspects the values in the "Referenced" fields
              for the VMAs shown in /proc/[pid]/smaps to get an  idea  of  the
              memory  footprint of the process.  One then clears the PG_Refer-
              enced and ACCESSED/YOUNG bits  and,  after  some  measured  time
              interval,  once  again  inspects  the values in the "Referenced"
              fields to get an idea of the change in memory footprint  of  the
              process during the measured interval.  If one is interested only
              in inspecting the selected mapping types, then the value 2 or  3
              can be used instead of 1.

              A further value can be written to affect a different bit:

              4 (since Linux 3.11)
                     Clear  the  soft-dirty  bit  for all the pages associated
                     with the process.  This  is  used  (in  conjunction  with
                     /proc/[pid]/pagemap) by the check-point restore system to
                     discover which pages of a process have been dirtied since
                     the file /proc/[pid]/clear_refs was written to.

              Writing  any  value  to  /proc/[pid]/clear_refs other than those
              listed above has no effect.

              The /proc/[pid]/clear_refs file is  present  only  if  the  CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/[pid]/cmdline
              This  read-only  file  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]/comm (since Linux 2.6.33)
              This file exposes the process's comm value--that is, the command
              name associated with the process.  Different threads in the same
              process  may  have  different  comm   values,   accessible   via
              /proc/[pid]/task/[tid]/comm.   A  thread  may  modify  its  comm
              value, or that of any of other thread in the same  thread  group
              (see  the discussion of CLONE_THREAD in clone(2)), by writing to
              the  file  /proc/self/task/[tid]/comm.   Strings   longer   than
              TASK_COMM_LEN (16) characters are silently truncated.

              This  file  provides  a superset of the prctl(2) PR_SET_NAME and
              PR_GET_NAME operations, and is employed by pthread_setname_np(3)
              when used to rename threads other than the caller.

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

       /proc/[pid]/cpuset (since Linux 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:

                  $ strings /proc/1/environ

       /proc/[pid]/exe
              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/[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  sym-
              bolic link are not available if the main thread has already ter-
              minated (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, and so on.

              For file descriptors for pipes and sockets, the entries will  be
              symbolic links whose content is the file type with the inode.  A
              readlink(2) call on this file returns a string in the format:

                  type:[inode]

              For example, socket:[2248868] will be a socket and its inode  is
              2248868.   For  sockets,  that  inode  can  be used to find more
              information in one of the files under /proc/net/.

              For file descriptors that have  no  corresponding  inode  (e.g.,
              file  descriptors  produced by epoll_create(2), eventfd(2), ino-
              tify_init(2), signalfd(2), and timerfd(2)), the entry will be  a
              symbolic link with contents of the form

                  anon_inode:<file-type>

              In some cases, the file-type is surrounded by square brackets.

              For  example, an epoll file descriptor will have a symbolic link
              whose content is the string anon_inode:[eventpoll].

              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/[pid]/fd.  For example, assum-
              ing 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
              as:

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

       /proc/[pid]/fdinfo/ (since Linux 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/[pid]/io (since kernel 2.6.20)
              This file contains I/O statistics for the process, for example:

                  # cat /proc/3828/io
                  rchar: 323934931
                  wchar: 323929600
                  syscr: 632687
                  syscw: 632675
                  read_bytes: 0
                  write_bytes: 323932160
                  cancelled_write_bytes: 0

              The fields are as follows:

              rchar: characters read
                     The number of bytes which this task has caused to be read
                     from storage.  This is simply the sum of bytes which this
                     process passed to read(2) and similar system  calls.   It
                     includes things such as terminal I/O and is unaffected by
                     whether or not actual physical disk I/O was required (the
                     read might have been satisfied from pagecache).

              wchar: characters written
                     The  number of bytes which this task has caused, or shall
                     cause to be written to disk.  Similar caveats apply  here
                     as with rchar.

              syscr: read syscalls
                     Attempt  to count the number of read I/O operations--that
                     is, system calls such as read(2) and pread(2).

              syscw: write syscalls
                     Attempt to count the number of write I/O operations--that
                     is, system calls such as write(2) and pwrite(2).

              read_bytes: bytes read
                     Attempt  to  count the number of bytes which this process
                     really did cause to be fetched from  the  storage  layer.
                     This is accurate for block-backed filesystems.

              write_bytes: bytes written
                     Attempt  to  count the number of bytes which this process
                     caused to be sent to the storage layer.

              cancelled_write_bytes:
                     The big inaccuracy here is truncate.  If a process writes
                     1MB  to a file and then deletes the file, it will in fact
                     perform no writeout.  But it will have been accounted  as
                     having  caused  1MB of write.  In other words: this field
                     represents the number of bytes which this process  caused
                     to not happen, by truncating pagecache.  A task can cause
                     "negative" I/O too.  If this task  truncates  some  dirty
                     pagecache, some I/O which another task has been accounted
                     for (in its write_bytes) will not be happening.

              Note: In the current implementation, things are a  bit  racy  on
              32-bit  systems:  if  process A reads process B's /proc/[pid]/io
              while process B  is  updating  one  of  these  64-bit  counters,
              process A could see an intermediate result.

       /proc/[pid]/gid_map (since Linux 3.5)
              See the description of /proc/[pid]/uid_map.

       /proc/[pid]/limits (since Linux 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)).   Up to and including Linux 2.6.35, this file is pro-
              tected to allow reading only by the real  UID  of  the  process.
              Since  Linux  2.6.36,  this file is readable by all users on the
              system.

       /proc/[pid]/map_files/ (since kernel 3.3)
              This subdirectory  contains  entries  corresponding  to  memory-
              mapped  files (see mmap(2)).  Entries are named by memory region
              start and end address pair (expressed as  hexadecimal  numbers),
              and  are symbolic links to the mapped files themselves.  Here is
              an example, with the output wrapped and reformatted to fit on an
              80-column display:

                  $ ls -l /proc/self/map_files/
                  lr--------. 1 root root 64 Apr 16 21:31
                              3252e00000-3252e20000 -> /usr/lib64/ld-2.15.so
                  ...

              Although  these entries are present for memory regions that were
              mapped with the MAP_FILE flag, the way anonymous  shared  memory
              (regions created with the MAP_ANON | MAP_SHARED flags) is imple-
              mented in Linux means that such  regions  also  appear  on  this
              directory.   Here  is  an  example  where the target file is the
              deleted /dev/zero one:

                  lrw-------. 1 root root 64 Apr 16 21:33
                              7fc075d2f000-7fc075e6f000 -> /dev/zero (deleted)

              This directory appears  only  if  the  CONFIG_CHECKPOINT_RESTORE
              kernel configuration option is enabled.

       /proc/[pid]/maps
              A  file containing the currently mapped memory regions and their
              access permissions.  See mmap(2) for  some  further  information
              about memory mappings.

              The format of the file is:

       address           perms offset  dev   inode       pathname
       00400000-00452000 r-xp 00000000 08:02 173521      /usr/bin/dbus-daemon
       00651000-00652000 r--p 00051000 08:02 173521      /usr/bin/dbus-daemon
       00652000-00655000 rw-p 00052000 08:02 173521      /usr/bin/dbus-daemon
       00e03000-00e24000 rw-p 00000000 00:00 0           [heap]
       00e24000-011f7000 rw-p 00000000 00:00 0           [heap]
       ...
       35b1800000-35b1820000 r-xp 00000000 08:02 135522  /usr/lib64/ld-2.15.so
       35b1a1f000-35b1a20000 r--p 0001f000 08:02 135522  /usr/lib64/ld-2.15.so
       35b1a20000-35b1a21000 rw-p 00020000 08:02 135522  /usr/lib64/ld-2.15.so
       35b1a21000-35b1a22000 rw-p 00000000 00:00 0
       35b1c00000-35b1dac000 r-xp 00000000 08:02 135870  /usr/lib64/libc-2.15.so
       35b1dac000-35b1fac000 ---p 001ac000 08:02 135870  /usr/lib64/libc-2.15.so
       35b1fac000-35b1fb0000 r--p 001ac000 08:02 135870  /usr/lib64/libc-2.15.so
       35b1fb0000-35b1fb2000 rw-p 001b0000 08:02 135870  /usr/lib64/libc-2.15.so
       ...
       f2c6ff8c000-7f2c7078c000 rw-p 00000000 00:00 0    [stack:986]
       ...
       7fffb2c0d000-7fffb2c2e000 rw-p 00000000 00:00 0   [stack]
       7fffb2d48000-7fffb2d49000 r-xp 00000000 00:00 0   [vdso]

              The  address  field is the address space in the process that the
              mapping occupies.  The perms field is a set of permissions:

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

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

              The  pathname field will usually be the file that is backing the
              mapping.  For ELF files, you can easily coordinate with the off-
              set  field  by  looking  at  the Offset field in the ELF program
              headers (readelf -l).

              There are additional helpful pseudo-paths:

                   [stack]
                          The  initial  process's  (also  known  as  the  main
                          thread's) stack.

                   [stack:<tid>] (since Linux 3.4)
                          A  thread's  stack (where the <tid> is a thread ID).
                          It corresponds to the /proc/[pid]/task/[tid]/ path.

                   [vdso] The virtual dynamically linked shared object.

                   [heap] The process's heap.

              If the pathname field is blank, this is an anonymous mapping  as
              obtained  via  the  mmap(2)  function.   There is no easy way to
              coordinate this back to a process's source, short of running  it
              through gdb(1), strace(1), or similar.

              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  filesystem  (see
                   stat(2)).

              (4)  root: root of the mount within the filesystem.

              (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)  filesystem type: name of filesystem in the form "type[.sub-
                   type]".

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

              (11) super options: per-superblock 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  Linux kernel source
              tree.

       /proc/[pid]/mounts (since Linux 2.4.19)
              This is a list of all the filesystems currently mounted  in  the
              process's  mount  namespace.   The  format of this file is docu-
              mented 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 filesystem 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.   See
              namespaces(7) for more information.

       /proc/[pid]/mountstats (since Linux 2.6.17)
              This  file exports information (statistics, configuration infor-
              mation) about the mount points in the process's mount namespace.
              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 filesystem tree.

              (3)  The filesystem type.

              (4)  Optional statistics and  configuration  information.   Cur-
                   rently  (as  at  Linux 2.6.26), only NFS filesystems export
                   information via this field.

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

              See namespaces(7) for more information.

       /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 more informa-
              tion, see namespaces(7).

       /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.

              Since  Linux  2.6.36, use of this file is deprecated in favor of
              /proc/[pid]/oom_score_adj.

       /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  adjustment specified by the
              oom_score_adj or oom_adj setting for the process.

       /proc/[pid]/oom_score_adj (since Linux 2.6.36)
              This file can be used to adjust the badness  heuristic  used  to
              select which process gets killed in out-of-memory conditions.

              The  badness  heuristic  assigns  a value to each candidate task
              ranging from 0 (never kill) to 1000 (always kill)  to  determine
              which  process  is targeted.  The units are roughly a proportion
              along that range of allowed  memory  the  process  may  allocate
              from, based on an estimation of its current memory and swap use.
              For example, if a task is using all allowed memory, its  badness
              score  will be 1000.  If it is using half of its allowed memory,
              its score will be 500.

              There is an additional factor included  in  the  badness  score:
              root processes are given 3% extra memory over other tasks.

              The  amount  of "allowed" memory depends on the context in which
              the OOM-killer was called.  If it is due to the memory  assigned
              to  the  allocating  task's  cpuset being exhausted, the allowed
              memory represents the set of mems assigned to that  cpuset  (see
              cpuset(7)).   If  it  is  due  to  a  mempolicy's  node(s) being
              exhausted, the allowed memory represents the  set  of  mempolicy
              nodes.   If  it  is  due to a memory limit (or swap limit) being
              reached, the allowed memory is that configured limit.   Finally,
              if  it  is  due  to  the  entire system being out of memory, the
              allowed memory represents all allocatable resources.

              The value of oom_score_adj is added to the badness score  before
              it  is  used to determine which task to kill.  Acceptable values
              range    from     -1000     (OOM_SCORE_ADJ_MIN)     to     +1000
              (OOM_SCORE_ADJ_MAX).   This  allows  user  space  to control the
              preference for OOM-killing, ranging  from  always  preferring  a
              certain  task  or completely disabling it from OOM killing.  The
              lowest possible value, -1000, is equivalent  to  disabling  OOM-
              killing  entirely  for  that task, since it will always report a
              badness score of 0.

              Consequently, it is very simple for user  space  to  define  the
              amount   of  memory  to  consider  for  each  task.   Setting  a
              oom_score_adj value of +500, for example, is roughly  equivalent
              to  allowing  the  remainder  of  tasks sharing the same system,
              cpuset, mempolicy, or memory  controller  resources  to  use  at
              least  50%  more  memory.   A  value of -500, on the other hand,
              would be roughly equivalent to discounting  50%  of  the  task's
              allowed  memory  from  being  considered  as scoring against the
              task.

              For    backward    compatibility    with    previous    kernels,
              /proc/[pid]/oom_adj can still be used to tune the badness score.
              Its value is scaled linearly with oom_score_adj.

              Writing to /proc/[pid]/oom_score_adj or /proc/[pid]/oom_adj will
              change the other with its scaled value.

       /proc/[pid]/pagemap (since Linux 2.6.25)
              This  file  shows  the  mapping of each of the process's virtual
              pages into physical page frames or swap area.  It  contains  one
              64-bit  value  for  each virtual page, with the bits set as fol-
              lows:

                   63     If set, the page is present in RAM.

                   62     If set, the page is in swap space

                   61 (since Linux 3.5)
                          The page is a file-mapped page or a shared anonymous
                          page.

                   60-56 (since Linux 3.11)
                          Zero

                   55 (Since Linux 3.11)
                          PTE  is soft-dirty (see the kernel source file Docu-
                          mentation/vm/soft-dirty.txt).

                   54-0   If the page is present in RAM (bit 63),  then  these
                          bits  provide  the  page  frame number, which can be
                          used to index /proc/kpageflags and /proc/kpagecount.
                          If  the  page is present in swap (bit 62), then bits
                          4-0 give the swap type, and  bits  54-5  encode  the
                          swap offset.

              Before Linux 3.11, bits 60-55 were used to encode the base-2 log
              of the page size.

              To employ /proc/[pid]/pagemap efficiently, use  /proc/[pid]/maps
              to  determine which areas of memory are actually mapped and seek
              to skip over unmapped regions.

              The  /proc/[pid]/pagemap  file  is  present  only  if  the  CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/[pid]/personality (since Linux 2.6.28)
              This  read-only  file exposes the process's execution domain, as
              set by personality(2).  The value is  displayed  in  hexadecimal
              notation.

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

              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.  (The pmap(1) command displays similar information, in
              a form that may be easier for parsing.)  For each mapping  there
              is a series of lines such as the following:

                  00400000-0048a000 r-xp 00000000 fd:03 960637       /bin/bash
                  Size:                552 kB
                  Rss:                 460 kB
                  Pss:                 100 kB
                  Shared_Clean:        452 kB
                  Shared_Dirty:          0 kB
                  Private_Clean:         8 kB
                  Private_Dirty:         0 kB
                  Referenced:          460 kB
                  Anonymous:             0 kB
                  AnonHugePages:         0 kB
                  Swap:                  0 kB
                  KernelPageSize:        4 kB
                  MMUPageSize:           4 kB
                  Locked:                0 kB

              The  first  of these lines shows the same information as is dis-
              played 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  ("Rss"),  the  process'  proportional
              share  of  this  mapping  ("Pss"), the number of clean and dirty
              shared pages in the mapping, and the number of clean  and  dirty
              private pages in the mapping.  "Referenced" indicates the amount
              of memory currently marked as referenced or  accessed.   "Anony-
              mous"  shows  the  amount  of memory that does not belong to any
              file.  "Swap" shows how much would-be-anonymous memory  is  also
              used, but out on swap.

              The  "KernelPageSize"  entry is the page size used by the kernel
              to back a VMA.  This matches the size used by  the  MMU  in  the
              majority of cases.  However, one counter-example occurs on PPC64
              kernels whereby a kernel using 64K as a base page size may still
              use  4K  pages for the MMU on older processors.  To distinguish,
              this patch reports "MMUPageSize" as the page size  used  by  the
              MMU.

              The  "Locked"  indicates whether the mapping is locked in memory
              or not.

              "VmFlags" field represents the kernel flags associated with  the
              particular  virtual  memory  area  in two letter encoded manner.
              The codes are the following:

                  rd  - readable
                  wr  - writable
                  ex  - executable
                  sh  - shared
                  mr  - may read
                  mw  - may write
                  me  - may execute
                  ms  - may share
                  gd  - stack segment grows down
                  pf  - pure PFN range
                  dw  - disabled write to the mapped file
                  lo  - pages are locked in memory
                  io  - memory mapped I/O area
                  sr  - sequential read advise provided
                  rr  - random read advise provided
                  dc  - do not copy area on fork
                  de  - do not expand area on remapping
                  ac  - area is accountable
                  nr  - swap space is not reserved for the area
                  ht  - area uses huge tlb pages
                  nl  - non-linear mapping
                  ar  - architecture specific flag
                  dd  - do not include area into core dump
                  sd  - soft-dirty flag
                  mm  - mixed map area
                  hg  - huge page advise flag
                  nh  - no-huge page advise flag
                  mg  - mergeable advise flag

              The  /proc/[pid]/smaps  file  is  present  only  if   the   CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/[pid]/stack (since Linux 2.6.29)
              This  file  provides  a  symbolic trace of the function calls in
              this process's kernel stack.  This file is provided only if  the
              kernel   was  built  with  the  CONFIG_STACKTRACE  configuration
              option.

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

              The  fields,  in order, with their proper scanf(3) format speci-
              fiers, are:

              (1) pid  %d
                        The process ID.

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

              (3) state  %c
                        One of the following  characters,  indicating  process
                        state:

                        R  Running

                        S  Sleeping in an interruptible wait

                        D  Waiting in uninterruptible disk sleep

                        Z  Zombie

                        T  Stopped  (on  a  signal)  or  (before Linux 2.6.33)
                           trace stopped

                        t  Tracing stop (Linux 2.6.33 onward)

                        W  Paging (only before Linux 2.6.0)

                        X  Dead (from Linux 2.6.0 onward)

                        x  Dead (Linux 2.6.33 to 3.13 only)

                        K  Wakekill (Linux 2.6.33 to 3.13 only)

                        W  Waking (Linux 2.6.33 to 3.13 only)

                        P  Parked (Linux 3.9 to 3.13 only)

              (4) ppid  %d
                        The PID of the parent of this process.

              (5) pgrp  %d
                        The process group ID of the process.

              (6) session  %d
                        The session ID of the process.

              (7) 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.)

              (8) tpgid  %d
                        The ID of the foreground process group of the control-
                        ling terminal of the process.

              (9) flags  %u
                        The kernel flags word of the process.  For  bit  mean-
                        ings,  see the PF_* defines in the Linux kernel source
                        file include/linux/sched.h.   Details  depend  on  the
                        kernel version.

                        The format for this field was %lu before Linux 2.6.

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

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

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

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

              (14) 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 cal-
                        culations.

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

              (16) 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).

              (17) 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)).

              (18) 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 (setpri-
                        ority(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.

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

              (20) 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.

              (21) 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.

              (22) starttime  %llu
                        The time the process started after  system  boot.   In
                        kernels  before Linux 2.6, this value was expressed in
                        jiffies.  Since Linux 2.6, the value is  expressed  in
                        clock ticks (divide by sysconf(_SC_CLK_TCK)).

                        The format for this field was %lu before Linux 2.6.

              (23) vsize  %lu
                        Virtual memory size in bytes.

              (24) 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.

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

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

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

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

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

              (30) kstkeip  %lu
                        The current EIP (instruction pointer).

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

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

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

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

              (35) wchan  %lu
                        This is the "channel" in which the process is waiting.
                        It is the address of a location in  the  kernel  where
                        the  process  is sleeping.  The corresponding symbolic
                        name can be found in /proc/[pid]/wchan.

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

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

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

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

              (40) rt_priority  %u  (since Linux 2.5.19)
                        Real-time scheduling priority, a number in the range 1
                        to  99  for processes scheduled under a real-time pol-
                        icy,  or   0,   for   non-real-time   processes   (see
                        sched_setscheduler(2)).

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

                        The format for this field was %lu before Linux 2.6.22.

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

              (43) 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)).

              (44) 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)).

              (45) start_data  %lu  (since Linux 3.3)
                        Address above which program initialized and uninitial-
                        ized (BSS) data are placed.

              (46) end_data  %lu  (since Linux 3.3)
                        Address below which program initialized and uninitial-
                        ized (BSS) data are placed.

              (47) start_brk  %lu  (since Linux 3.3)
                        Address above which program heap can be expanded  with
                        brk(2).

              (48) arg_start  %lu  (since Linux 3.5)
                        Address  above  which  program  command-line arguments
                        (argv) are placed.

              (49) arg_end  %lu  (since Linux 3.5)
                        Address below program  command-line  arguments  (argv)
                        are placed.

              (50) env_start  %lu  (since Linux 3.5)
                        Address above which program environment is placed.

              (51) env_end  %lu  (since Linux 3.5)
                        Address below which program environment is placed.

              (52) exit_code  %d  (since Linux 3.5)
                        The thread's exit status in the form reported by wait-
                        pid(2).

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

                  size       (1) total program size
                             (same as VmSize in /proc/[pid]/status)
                  resident   (2) resident set size
                             (same as VmRSS in /proc/[pid]/status)
                  share      (3) shared pages (i.e., backed by a file)
                  text       (4) text (code)
                  lib        (5) library (unused in Linux 2.6)
                  data       (6) data + stack
                  dt         (7) 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  filesystem  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 capabili-
                ties(7)).

              * CapBnd: Capability Bounding set (since Linux 2.6.26, see capa-
                bilities(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_ctxt_switches, nonvoluntary_ctxt_switches: Number of
                voluntary  and  involuntary  context  switches  (since   Linux
                2.6.23).

       /proc/[pid]/syscall (since Linux 2.6.27)
              This  file exposes the system call number and argument registers
              for the system call currently being  executed  by  the  process,
              followed  by the values of the stack pointer and program counter
              registers.   The  values  of  all  six  argument  registers  are
              exposed, although most system calls use fewer registers.

              If  the  process  is blocked, but not in a system call, then the
              file displays -1 in place of the system call number, followed by
              just  the  values  of the stack pointer and program counter.  If
              process is not blocked, then file contains just the string "run-
              ning".

              This file is present only if the kernel was configured with CON-
              FIG_HAVE_ARCH_TRACEHOOK.

       /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] direc-
              tories.  For attributes that are shared by all threads, the con-
              tents 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  ter-
              minated (typically by calling pthread_exit(3)).

       /proc/[pid]/uid_map, /proc/[pid]/gid_map (since Linux 3.5)
              These  files  expose  the mappings for user and group IDs inside
              the user namespace for the process pid.   The  description  here
              explains  the  details for uid_map; gid_map is exactly the same,
              but each instance of "user ID" is replaced by "group ID".

              The uid_map file exposes the mapping of user IDs from  the  user
              namespace  of  the  process  pid  to  the  user namespace of the
              process that opened uid_map (but see  a  qualification  to  this
              point  below).   In other words, processes that are in different
              user namespaces will potentially see different values when read-
              ing  from  a  particular  uid_map file, depending on the user ID
              mappings for the user namespaces of the reading processes.

              Each line in the file specifies a 1-to-1 mapping of a  range  of
              contiguous  between  two  user namespaces.  The specification in
              each line takes the form of three  numbers  delimited  by  white
              space.   The  first  two numbers specify the starting user ID in
              each user namespace.  The third number specifies the  length  of
              the mapped range.  In detail, the fields are interpreted as fol-
              lows:

              (1) The start of the range of user IDs in the user namespace  of
                  the process pid.

              (2) The  start  of  the  range of user IDs to which the user IDs
                  specified by field one map.  How field  two  is  interpreted
                  depends  on  whether the process that opened uid_map and the
                  process pid are in the same user namespace, as follows:

                  a) If the two processes are in  different  user  namespaces:
                     field two is the start of a range of user IDs in the user
                     namespace of the process that opened uid_map.

                  b) If the two processes are  in  the  same  user  namespace:
                     field  two  is  the start of the range of user IDs in the
                     parent user namespace of the process pid.   (The  "parent
                     user namespace" is the user namespace of the process that
                     created a user namespace via  a  call  to  unshare(2)  or
                     clone(2) with the CLONE_NEWUSER flag.)  This case enables
                     the opener of uid_map (the common case  here  is  opening
                     /proc/self/uid_map)  to  see the mapping of user IDs into
                     the user namespace of the process that created this  user
                     namespace.

              (3) The  length  of the range of user IDs that is mapped between
                  the two user namespaces.

              After the creation of a new user namespace, the uid_map file may
              be written to exactly once to specify the mapping of user IDs in
              the new user namespace.  (An attempt to write more than once  to
              the file fails with the error EPERM.)

              The  lines  written  to  uid_map  must  conform to the following
              rules:

              *  The three fields must be valid numbers, and  the  last  field
                 must be greater than 0.

              *  Lines are terminated by newline characters.

              *  There  is  an (arbitrary) limit on the number of lines in the
                 file.  As at Linux 3.8, the limit is five lines.

              *  The range of user IDs specified in each line  cannot  overlap
                 with the ranges in any other lines.  In the current implemen-
                 tation (Linux 3.8), this requirement is satisfied by  a  sim-
                 plistic  implementation  that imposes the further requirement
                 that the values in both field 1 and  field  2  of  successive
                 lines must be in ascending numerical order.

              Writes that violate the above rules fail with the error EINVAL.

              In  order  for  a  process  to  write to the /proc/[pid]/uid_map
              (/proc/[pid]/gid_map) file, the following requirements  must  be
              met:

              *  The  process must have the CAP_SETUID (CAP_SETGID) capability
                 in the user namespace of the process pid.

              *  The process must have the CAP_SETUID (CAP_SETGID)  capability
                 in the parent user namespace.

              *  The  process  must  be  in  either  the user namespace of the
                 process pid or  inside  the  parent  user  namespace  of  the
                 process pid.
       For further details, see namespaces(7).

       /proc/[pid]/wchan (since Linux 2.6.0)
              The  symbolic  name  corresponding to the location in the kernel
              where the process is sleeping.

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

       /proc/buddyinfo
              This file contains information which is used for diagnosing mem-
              ory fragmentation issues.  Each line starts with the identifica-
              tion  of  the node and the name of the zone which together iden-
              tify a memory region This is  then  followed  by  the  count  of
              available  chunks  of  a  certain order in which these zones are
              split.  The size in bytes of a certain order  is  given  by  the
              formual:

                  (2^order) * PAGE_SIZE

              The  binary  buddy  allocator  algorithm  inside the kernel will
              split one chunk into two chunks of a smaller  order  (thus  with
              half  the size) or combine two contiguous chunks into one larger
              chunk of a higher order (thus with double the size)  to  satisfy
              allocation  requests  and  to counter memory fragmentation.  The
              order matches the column number, when starting to count at zero.

              For example on a x86_64 system:

  Node 0, zone     DMA     1    1    1    0    2    1    1    0    1    1    3
  Node 0, zone   DMA32    65   47    4   81   52   28   13   10    5    1  404
  Node 0, zone  Normal   216   55  189  101   84   38   37   27    5    3  587

              In this example, there is one node containing  three  zones  and
              there are 11 different chunk sizes.  If the page size is 4 kilo-
              byteis, then the first zone called DMA  (on  x86  the  first  16
              megabyte  of memory) has 1 chunk of 4 kilobytes (order 0) avail-
              able and has 3 chunks of 4 megabytes (order 10) available.

              If the memory is heavily fragmentated, the counters  for  higher
              order  chunks  will  be  zero and allocation of large contiguous
              areas will fail.

              Further information about the zones can be found in  /proc/zone-
              info.

       /proc/bus
              Contains subdirectories for installed busses.

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

       /proc/[pid]/timers (since Linux 3.10)
              A list of the POSIX timers for  this  process.   Each  timer  is
              listed  with  a  line  that  started with the string "ID:".  For
              example:

                  ID: 1
                  signal: 60/00007fff86e452a8
                  notify: signal/pid.2634
                  ClockID: 0
                  ID: 0
                  signal: 60/00007fff86e452a8
                  notify: signal/pid.2634
                  ClockID: 1

              The lines shown for each timer have the following meanings:

              ID     The ID for this timer.  This is not the same as the timer
                     ID  returned  by  timer_create(2); rather, it is the same
                     kernel-internal ID that is available via  the  si_timerid
                     field of the siginfo_t structure (see sigaction(2)).

              signal This is the signal number that this timer uses to deliver
                     notifications  followed  by  a  slash,   and   then   the
                     sigev_value.sival_ptr  value  supplied to the signal han-
                     dler.  Valid only for timers that notify via a signal.

              notify The part before the slash specifies  the  mechanism  that
                     this  timer  uses to deliver notifications, and is one of
                     "thread", "signal", or "none".  Immediately following the
                     slash   is  either  the  string  "tid"  for  timers  with
                     SIGEV_THREAD_ID notification, or "pid"  for  timers  that
                     notify by other mechanisms.  Following the "." is the PID
                     of the process that will be delivered  a  signal  if  the
                     timer delivers notifications via a signal.

              ClockID
                     This  field  identifies the clock that the timer uses for
                     measuring time.  For most clocks, this is a  number  that
                     matches  one  of the user-space CLOCK_* constants exposed
                     via <time.h>.   CLOCK_PROCESS_CPUTIME_ID  timers  display
                     with     a     value     of    -6    in    this    field.
                     CLOCK_THREAD_CPUTIME_ID timers display with a value of -2
                     in this field.

       /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 configur-
              ing the kernel (using make xconfig, make  config,  or  similar).
              The  file  contents  are  compressed;  view or search them using
              zcat(1) and zgrep(1).  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 provided only 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.
              The lscpu(1) command gathers its information from this file.

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

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

       /proc/fs
              Contains subdirectories that in turn contain files with informa-
              tion about (certain) mounted filesystems.

       /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  architec-
              tures,  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 dif-
              ferent 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 mes-
              sages.

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

       /proc/kpagecount (since Linux 2.6.25)
              This  file  contains  a 64-bit count of the number of times each
              physical page frame is mapped, indexed by page frame number (see
              the discussion of /proc/[pid]/pagemap).

              The   /proc/kpagecount   file   is  present  only  if  the  CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/kpageflags (since Linux 2.6.25)
              This file contains 64-bit masks corresponding to  each  physical
              page  frame; it is indexed by page frame number (see the discus-
              sion of /proc/[pid]/pagemap).  The bits are as follows:

                   0 - KPF_LOCKED
                   1 - KPF_ERROR
                   2 - KPF_REFERENCED
                   3 - KPF_UPTODATE
                   4 - KPF_DIRTY
                   5 - KPF_LRU
                   6 - KPF_ACTIVE
                   7 - KPF_SLAB
                   8 - KPF_WRITEBACK
                   9 - KPF_RECLAIM
                  10 - KPF_BUDDY
                  11 - KPF_MMAP           (since Linux 2.6.31)
                  12 - KPF_ANON           (since Linux 2.6.31)
                  13 - KPF_SWAPCACHE      (since Linux 2.6.31)
                  14 - KPF_SWAPBACKED     (since Linux 2.6.31)
                  15 - KPF_COMPOUND_HEAD  (since Linux 2.6.31)
                  16 - KPF_COMPOUND_TAIL  (since Linux 2.6.31)
                  16 - KPF_HUGE           (since Linux 2.6.31)
                  18 - KPF_UNEVICTABLE    (since Linux 2.6.31)
                  19 - KPF_HWPOISON       (since Linux 2.6.31)
                  20 - KPF_NOPAGE         (since Linux 2.6.31)
                  21 - KPF_KSM            (since Linux 2.6.32)
                  22 - KPF_THP            (since Linux 3.4)

              For further details on the meanings of these bits, see the  ker-
              nel  source  file  Documentation/vm/pagemap.txt.   Before kernel
              2.6.29, KPF_WRITEBACK, KPF_RECLAIM,  KPF_BUDDY,  and  KPF_LOCKED
              did not report correctly.

              The   /proc/kpageflags   file   is  present  only  if  the  CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /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  sepa-
              rated  by a slash (/).  The first of these is the number of cur-
              rently runnable kernel scheduling entities (processes, threads).
              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  present  only 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 mem-
              ory (both physical and swap) on the system as well as the shared
              memory  and  buffers  used by the kernel.  Each line of the file
              consists of a parameter name, followed by a colon, the value  of
              the  parameter,  and an option unit of measurement (e.g., "kB").
              The list below describes the  parameter  names  and  the  format
              specifier  required  to  read  the field value.  Except as noted
              below, all of the fields have been present since at least  Linux
              2.6.0.  Some fields are displayed only if the kernel was config-
              ured with various options; those dependencies are noted  in  the
              list.

              MemTotal %lu
                     Total usable RAM (i.e., physical RAM minus a few reserved
                     bits and the kernel binary code).

              MemFree %lu
                     The sum of LowFree+HighFree.

              Buffers %lu
                     Relatively temporary storage for  raw  disk  blocks  that
                     shouldn't get tremendously large (20MB or so).

              Cached %lu
                     In-memory  cache  for  files read from the disk (the page
                     cache).  Doesn't include SwapCached.

              SwapCached %lu
                     Memory that once was swapped out, is swapped back in  but
                     still  also  is in the swap file.  (If memory pressure is
                     high, these pages don't need  to  be  swapped  out  again
                     because  they  are  already in the swap file.  This saves
                     I/O.)

              Active %lu
                     Memory that has been used more recently and  usually  not
                     reclaimed unless absolutely necessary.

              Inactive %lu
                     Memory  which  has  been  less recently used.  It is more
                     eligible to be reclaimed for other purposes.

              Active(anon) %lu (since Linux 2.6.28)
                     [To be documented.]

              Inactive(anon) %lu (since Linux 2.6.28)
                     [To be documented.]

              Active(file) %lu (since Linux 2.6.28)
                     [To be documented.]

              Inactive(file) %lu (since Linux 2.6.28)
                     [To be documented.]

              Unevictable %lu (since Linux 2.6.28)
                     (From Linux 2.6.28 to 2.6.30, CONFIG_UNEVICTABLE_LRU  was
                     required.)  [To be documented.]

              Mlocked %lu (since Linux 2.6.28)
                     (From  Linux 2.6.28 to 2.6.30, CONFIG_UNEVICTABLE_LRU was
                     required.)  [To be documented.]

              HighTotal %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Total  amount  of  highmem.   Highmem is all memory above
                     ~860MB of physical memory.  Highmem areas are for use  by
                     user-space  programs,  or for the page cache.  The kernel
                     must use tricks to access this memory, making  it  slower
                     to access than lowmem.

              HighFree %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Amount of free highmem.

              LowTotal %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Total  amount  of  lowmem.  Lowmem is memory which can be
                     used for everything that highmem can be used for, but  it
                     is  also  available for the kernel's use for its own data
                     structures.  Among many other things, it is where  every-
                     thing  from  Slab  is  allocated.  Bad things happen when
                     you're out of lowmem.

              LowFree %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Amount of free lowmem.

              MmapCopy %lu (since Linux 2.6.29)
                     (CONFIG_MMU is required.)  [To be documented.]

              SwapTotal %lu
                     Total amount of swap space available.

              SwapFree %lu
                     Amount of swap space that is currently unused.

              Dirty %lu
                     Memory which is waiting to get written back to the disk.

              Writeback %lu
                     Memory which is actively being written back to the disk.

              AnonPages %lu (since Linux 2.6.18)
                     Non-file backed pages mapped into user-space page tables.

              Mapped %lu
                     Files  which have been mapped into memory (with mmap(2)),
                     such as libraries.

              Shmem %lu (since Linux 2.6.32)
                     [To be documented.]

              Slab %lu
                     In-kernel data structures cache.

              SReclaimable %lu (since Linux 2.6.19)
                     Part of Slab, that might be reclaimed, such as caches.

              SUnreclaim %lu (since Linux 2.6.19)
                     Part of Slab, that cannot be reclaimed  on  memory  pres-
                     sure.

              KernelStack %lu (since Linux 2.6.32)
                     Amount of memory allocated to kernel stacks.

              PageTables %lu (since Linux 2.6.18)
                     Amount  of  memory  dedicated to the lowest level of page
                     tables.

              Quicklists %lu (since Linux 2.6.27)
                     (CONFIG_QUICKLIST is required.)  [To be documented.]

              NFS_Unstable %lu (since Linux 2.6.18)
                     NFS pages sent to the server, but not  yet  committed  to
                     stable storage.

              Bounce %lu (since Linux 2.6.18)
                     Memory used for block device "bounce buffers".

              WritebackTmp %lu (since Linux 2.6.26)
                     Memory used by FUSE for temporary writeback buffers.

              CommitLimit %lu (since Linux 2.6.10)
                     This is the total amount of memory currently available to
                     be allocated on the system, expressed in kilobytes.  This
                     limit  is adhered to only if strict overcommit accounting
                     is enabled (mode  2  in  /proc/sys/vm/overcommit_memory).
                     The   limit   is  calculated  according  to  the  formula
                     described under /proc/sys/vm/overcommit_memory.  For fur-
                     ther  details,  see  the  kernel  source  file Documenta-
                     tion/vm/overcommit-accounting.

              Committed_AS %lu
                     The amount of memory presently allocated on  the  system.
                     The  committed memory is a sum of all of the memory which
                     has been allocated by processes, even if it has not  been
                     "used"  by them as of yet.  A process which allocates 1GB
                     of memory (using malloc(3) or similar), but touches  only
                     300MB  of that memory will show up as using only 300MB of
                     memory even if it has the address space allocated for the
                     entire 1GB.

                     This  1GB  is memory which has been "committed" to by the
                     VM and can be used at any time by the allocating applica-
                     tion.  With strict overcommit enabled on the system (mode
                     2 in  IR  /proc/sys/vm/overcommit_memory  ),  allocations
                     which would exceed the CommitLimit will not be permitted.
                     This is useful if one needs to guarantee  that  processes
                     will  not fail due to lack of memory once that memory has
                     been successfully allocated.

              VmallocTotal %lu
                     Total size of vmalloc memory area.

              VmallocUsed %lu
                     Amount of vmalloc area which is used.

              VmallocChunk %lu
                     Largest contiguous block of vmalloc area which is free.

              HardwareCorrupted %lu (since Linux 2.6.32)
                     (CONFIG_MEMORY_FAILURE is required.)  [To be documented.]

              AnonHugePages %lu (since Linux 2.6.38)
                     (CONFIG_TRANSPARENT_HUGEPAGE  is   required.)    Non-file
                     backed huge pages mapped into user-space page tables.

              HugePages_Total %lu
                     (CONFIG_HUGETLB_PAGE  is required.)  The size of the pool
                     of huge pages.

              HugePages_Free %lu
                     (CONFIG_HUGETLB_PAGE is required.)  The  number  of  huge
                     pages in the pool that are not yet allocated.

              HugePages_Rsvd %lu (since Linux 2.6.17)
                     (CONFIG_HUGETLB_PAGE is required.)  This is the number of
                     huge pages for which a commitment to  allocate  from  the
                     pool  has been made, but no allocation has yet been made.
                     These reserved huge pages guarantee that  an  application
                     will  be  able  to  allocate a huge page from the pool of
                     huge pages at fault time.

              HugePages_Surp %lu (since Linux 2.6.24)
                     (CONFIG_HUGETLB_PAGE is required.)  This is the number of
                     huge   pages   in   the   pool   above   the   value   in
                     /proc/sys/vm/nr_hugepages.  The maximum number of surplus
                     huge  pages  is  controlled  by  /proc/sys/vm/nr_overcom-
                     mit_hugepages.

              Hugepagesize %lu
                     (CONFIG_HUGETLB_PAGE is  required.)   The  size  of  huge
                     pages.

       /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  filesys-
              tems  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 docu-
              mented in fstab(5).

       /proc/mtrr
              Memory  Type  Range Registers.  See the Linux 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 struc-
              tures 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 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
              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  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.

       /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  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

       /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 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.

       /proc/partitions
              Contains  the  major and minor numbers of each partition as well
              as the number of 1024-byte blocks and the partition name.

       /proc/pci
              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 nonoptionally 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.

       /proc/profile (since Linux 2.4)
              This file is present only if the kernel was booted with the pro-
              file=1 command-line option.  It exposes kernel profiling  infor-
              mation  in  a  binary format for use by readprofile(1).  Writing
              (e.g., an empty string) to this file resets the profiling  coun-
              ters; on some architectures, writing a binary integer "profiling
              multiplier" of size sizeof(int)  sets  the  profiling  interrupt
              frequency.

       /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 sub-
              system 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 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.

       /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  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, and so on.

              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
              filesystem, 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  present  only 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 various states:

                     user   (1) Time spent in user mode.

                     nice   (2) Time spent in  user  mode  with  low  priority
                            (nice).

                     system (3) Time spent in system mode.

                     idle   (4)  Time  spent  in  the  idle  task.  This value
                            should be USER_HZ times the second  entry  in  the
                            /proc/uptime pseudo-file.

                     iowait (since Linux 2.5.41)
                            (5) Time waiting for I/O to complete.

                     irq (since Linux 2.6.0-test4)
                            (6) Time servicing interrupts.

                     softirq (since Linux 2.6.0-test4)
                            (7) Time servicing softirqs.

                     steal (since Linux 2.6.11)
                            (8)  Stolen time, which is the time spent in other
                            operating systems when running  in  a  virtualized
                            environment

                     guest (since Linux 2.6.24)
                            (9)  Time  spent  running  a virtual CPU for guest
                            operating systems under the control of  the  Linux
                            kernel.

                     guest_nice (since Linux 2.6.33)
                            (10) Time spent running a niced guest (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
                     including unnumbered  architecture  specific  interrupts;
                     each  subsequent  column is the total for that particular
                     numbered interrupt.  Unnumbered interrupts are not shown,
                     only summed into the total.

              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
              filesystem, and the (deprecated) sysctl(2) system call.

       /proc/sys/abi (since Linux 2.4.10)
              This directory may contain files with application binary  infor-
              mation.    See   the   Linux   kernel   source  file  Documenta-
              tion/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 filesystems.

       /proc/sys/fs/binfmt_misc
              Documentation for files in this directory can be  found  in  the
              Linux 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 in the kernel log about running  out  of  file  handles
              (look  for "VFS: file-max limit <number> reached"), try increas-
              ing 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.

              Privileged  processes  (CAP_SYS_ADMIN) can override the file-max
              limit.

       /proc/sys/fs/file-nr
              This (read-only) file contains  three  numbers:  the  number  of
              allocated  file  handles  (i.e.,  the  number of files presently
              opened); the number of free file handles; and the maximum number
              of file handles (i.e., the same value as /proc/sys/fs/file-max).
              If the number of allocated file handles is close to the maximum,
              you  should  consider increasing the maximum.  Before Linux 2.6,
              the kernel allocated file handles  dynamically,  but  it  didn't
              free  them  again.  Instead the free file handles were kept in a
              list for reallocation; the "free file handles"  value  indicates
              the  size  of  that  list.   A large number of free file handles
              indicates that there was a past peak in the usage of  open  file
              handles.  Since Linux 2.6, the kernel does deallocate freed file
              handles, and the "free file handles" value is always zero.

       /proc/sys/fs/inode-max (only present until Linux 2.2)
              This file contains the maximum number of in-memory inodes.  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.

              Starting with Linux 2.4, there is no longer a  static  limit  on
              the number of inodes, and this file is removed.

       /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 (always zero).

              nr_inodes is the number of  inodes  the  system  has  allocated.
              nr_free_inodes represents the number of free inodes.

              preshrink is nonzero when the nr_inodes > inode-max and the sys-
              tem needs to prune the inode list instead  of  allocating  more;
              since Linux 2.4, this field is a dummy value (always zero).

       /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).

       /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 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.

       /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  filesystems  support  only
              16-bit  UIDs  and  GIDs,  although in Linux UIDs and GIDs are 32
              bits.  When one of these  filesystems  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/protected_hardlinks (since Linux 3.6)
              When the value in this file is 0, no restrictions are placed  on
              the  creation of hard links (i.e., this is the historical behav-
              ior before Linux 3.6).  When the value in this file is 1, a hard
              link  can be created to a target file only if one of the follow-
              ing conditions is true:

              *  The caller has the CAP_FOWNER capability.

              *  The filesystem UID of the process creating the  link  matches
                 the  owner  (UID) of the target file (as described in creden-
                 tials(7), a process's filesystem UID is normally the same  as
                 its effective UID).

              *  All of the following conditions are true:

                  o  the target is a regular file;

                  o  the  target file does not have its set-user-ID permission
                     bit enabled;

                  o  the target file does not have both its  set-group-ID  and
                     group-executable permission bits enabled; and

                  o  the  caller  has  permission to read and write the target
                     file (either via the file's permissions mask  or  because
                     it has suitable capabilities).

              The  default  value  in  this file is 0.  Setting the value to 1
              prevents a longstanding class of security issues caused by hard-
              link-based  time-of-check, time-of-use races, most commonly seen
              in world-writable directories such as /tmp.  The  common  method
              of  exploiting  this  flaw is to cross privilege boundaries when
              following a given hard link (i.e., a root process follows a hard
              link created by another user).  Additionally, on systems without
              separated partitions, this stops unauthorized users  from  "pin-
              ning"  vulnerable  set-user-ID  and  set-group-ID  files against
              being upgraded by  the  administrator,  or  linking  to  special
              files.

       /proc/sys/fs/protected_symlinks (since Linux 3.6)
              When  the value in this file is 0, no restrictions are placed on
              following symbolic links (i.e., this is the historical  behavior
              before  Linux  3.6).  When the value in this file is 1, symbolic
              links are followed only in the following circumstances:

              *  the filesystem UID of the process following the link  matches
                 the owner (UID) of the symbolic link (as described in creden-
                 tials(7), a process's filesystem UID is normally the same  as
                 its effective UID);

              *  the link is not in a sticky world-writable directory; or

              *  the  symbolic  link  and  its  parent directory have the same
                 owner (UID)

              A system call that fails to follow a symbolic  link  because  of
              the above restrictions returns the error EACCES in errno.

              The  default  value  in  this file is 0.  Setting the value to 1
              avoids a longstanding class of security issues based on time-of-
              check, time-of-use races when accessing symbolic links.

       /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) behav-
                     ior.  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  filesystem 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.

                     Additionally, since Linux 3.6, /proc/sys/kernel/core_pat-
                     tern must either be an absolute pathname or a  pipe  com-
                     mand,  as  detailed in core(5).  Warnings will be written
                     to the kernel log if core_pattern does not  follow  these
                     rules, and no core dump will be produced.

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

       /proc/sys/fs/super-nr
              This file contains the number of filesystems 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 fre-
              quency.  If BSD-style process accounting is enabled, these  val-
              ues control its behavior.  If free space on filesystem 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_last_cap (since Linux 3.2)
              See capabilities(7).

       /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).

       /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 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.

       /proc/sys/kernel/dmesg_restrict (since Linux 2.6.37)
              The value in this file determines who can see kernel syslog con-
              tents.  A value of 0 in this file imposes no  restrictions.   If
              the  value  is 1, only privileged users can read the kernel sys-
              log.  (See syslog(2) for more details.)  Since Linux  3.4,  only
              users  with the CAP_SYS_ADMIN capability may change the value in
              this file.

       /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.

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

       /proc/sys/kernel/kptr_restrict (since Linux 2.6.38)
              The value in this file determines whether kernel  addresses  are
              exposed  via  /proc files and other interfaces.  A value of 0 in
              this file imposes no restrictions.  If the value  is  1,  kernel
              pointers printed using the %pK format specifier will be replaced
              with zeros unless the user has the  CAP_SYSLOG  capability.   If
              the  value  is  2,  kernel pointers printed using the %pK format
              specifier will be replaced with zeros regardless of  the  user's
              capabilities.   The  initial  default value for this file was 1,
              but the default was changed to 0 in Linux 2.6.39.   Since  Linux
              3.4, only users with the CAP_SYS_ADMIN capability can change the
              value in this file.

       /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 present only if
              the kernel is built  with  the  CONFIG_MODULES  (CONFIG_KMOD  in
              Linux  2.6.26  and  earlier) option enabled.  It is described by
              the Linux kernel  source  file  Documentation/kmod.txt  (present
              only in kernel 2.4 and earlier).

       /proc/sys/kernel/modules_disabled (since Linux 2.6.31)
              A toggle value indicating if modules are allowed to be loaded in
              an otherwise modular kernel.  This toggle defaults to  off  (0),
              but  can  be  set  true  (1).  Once true, modules can be neither
              loaded nor unloaded, and the toggle cannot be set back to false.
              The  file  is  present only if the kernel is built with the CON-
              FIG_MODULES option enabled.

       /proc/sys/kernel/msgmax (since Linux 2.2)
              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.

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

       /proc/sys/kernel/msgmnb (since Linux 2.2)
              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/ngroups_max (since Linux 2.6.4)
              This is a read-only file that displays the upper  limit  on  the
              number of a process's group memberships.

       /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  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
              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).
              PIDs  greater than this value are not allocated; thus, the value
              in this file also acts as a system-wide limit on the total  num-
              ber  of processes and threads.  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
              See syslog(2).

       /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 cur-
              rently in use.

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

       /proc/sys/kernel/random/uuid (since Linux 2.4)
              Each read from this read-only file returns a randomly  generated
              128-bit UUID, as a string in the standard UUID format.

       /proc/sys/kernel/real-root-dev
              This file is documented in the Linux kernel source file Documen-
              tation/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/sched_rr_timeslice_ms (since Linux 3.9)
              See sched_rr_get_interval(2).

       /proc/sys/kernel/sched_rt_period_us (Since Linux 2.6.25)
              See sched(7).

       /proc/sys/kernel/sched_rt_runtime_us (Since Linux 2.6.25)
              See sched(7).

       /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/shm_rmid_forced (since Linux 3.1)
              If  this  file  is set to 1, all System V shared memory segments
              will be marked for destruction as soon as the number of attached
              processes  falls to zero; in other words, it is no longer possi-
              ble to create shared memory segments that exist independently of
              any attached process.

              The effect is as though a shmctl(2) IPC_RMID is performed on all
              existing segments as well as all segments created in the  future
              (until  this  file  is reset to 0).  Note that existing segments
              that are attached to no process will  be  immediately  destroyed
              when  this  file  is  set  to  1.  Setting this option will also
              destroy segments that were created,  but  never  attached,  upon
              termination  of  the  process  that  created  the  segment  with
              shmget(2).

              Setting this file to 1 provides a way of ensuring that all  Sys-
              tem  V  shared  memory segments are counted against the resource
              usage and resource limits (see the description of  RLIMIT_AS  in
              getrlimit(2)) of at least one process.

              Because  setting  this  file to 1 produces behavior that is non-
              standard and could also break existing applications, the default
              value  in this file is 0.  Only set this file to 1 if you have a
              good understanding of the semantics of  the  applications  using
              System V shared memory on your system.

       /proc/sys/kernel/shmall (since Linux 2.2)
              This  file contains the system-wide limit on the total number of
              pages of System V shared memory.

       /proc/sys/kernel/shmmax (since Linux 2.2)
              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 (since Linux 2.4)
              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 specifi-
              cally 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 - bit mask 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  signaling of processes (term, kill, oom-
              kill)
                      128 - allow reboot/poweroff
                      256 - allow nicing of all real-time tasks

              This file is present only if the CONFIG_MAGIC_SYSRQ kernel  con-
              figuration option is enabled.  For further details see the Linux
              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
              filesystem (NFS).  On some systems, it is not present.

       /proc/sys/vm
              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
              free.  This can be useful for memory management testing and per-
              forming  reproducible filesystem benchmarks.  Because writing to
              this file causes the benefits of caching  to  be  lost,  it  can
              degrade overall system performance.

              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  writing  to this file is a nondestructive operation and
              dirty objects are not freeable,  the  user  should  run  sync(1)
              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 han-
              dled 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 affect-
              ing  any applications.  But if there is no other up-to-date copy
              of the data, it will kill processes to prevent any data  corrup-
              tions from propagating.

              The file has one of the following values:

              1:  Kill  all  processes that have the corrupted-and-not-reload-
                  able 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 kill
                  only a process that 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  active  only  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_MEM-
              ORY_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_MEM-
              ORY_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 pos-
              sibly 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_allocat-
              ing_task.

              The default value is 0.

       /proc/sys/vm/overcommit_kbytes (since Linux 3.14)
              This writable file provides an alternative to /proc/sys/vm/over-
              commit_ratio    for    controlling    the    CommitLimit    when
              /proc/sys/vm/overcommit_memory has the value 2.  It  allows  the
              amount  of  memory overcommitting to be specified as an absolute
              value (in kB), rather than as a  percentage,  as  is  done  with
              overcommit_ratio.  This allows for finer-grained control of Com-
              mitLimit on systems with extremely large memory sizes.

              Only one of overcommit_kbytes or overcommit_ratio  can  have  an
              effect:  if  overcommit_kbytes  has  a nonzero value, then it is
              used to calculate  CommitLimit,  otherwise  overcommit_ratio  is
              used.  Writing a value to either of these files causes the value
              in the other file to be set to zero.

       /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  get-
              ting 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  that  can  be allocated (CommitLimit in /proc/meminfo) is
              calculated as

                  CommitLimit = (total_RAM - total_huge_TLB) *
                                overcommit_ratio / 100 + total_swap

              where:

                   *  total_RAM is the total amount of RAM on the system;

                   *  total_huge_TLB is the amount of  memory  set  aside  for
                      huge pages;

                   *  overcommit_ratio  is  the value in /proc/sys/vm/overcom-
                      mit_ratio; and

                   *  total_swap is the amount of swap space.

              For example, on a system with 16GB  of  physical  RAM,  16GB  of
              swap,  no space dedicated to huge pages, and an overcommit_ratio
              of 50, this formula yields a CommitLimit of 24GB.

              Since Linux 3.14, if the value in /proc/sys/vm/overcommit_kbytes
              is nonzero, then CommitLimit is instead calculated as:

                  CommitLimit = overcommit_kbytes + total_swap

       /proc/sys/vm/overcommit_ratio (since Linux 2.6.0)
              This  writable  file defines a percentage by which memory can be
              overcommitted.  The default value in the file is  50.   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-
              uation.

              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 func-
              tion as typing ALT-SysRq-<character>  (see  the  description  of
              /proc/sys/kernel/sysrq).  This file is normally writable only by
              root.  For further details see the Linux kernel source file Doc-
              umentation/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/timer_list (since Linux 2.6.21)
              This read-only file exposes a  list  of  all  currently  pending
              (high-resolution)  timers,  all  clock-event  sources, and their
              parameters in a human-readable form.

       /proc/timer_stats (since Linux 2.6.21)
              This is a debugging facility to make timer (ab)use  in  a  Linux
              system  visible  to kernel and user-space developers.  It can be
              used by kernel and user-space developers to  verify  that  their
              code  does  not  make undue use of timers.  The goal is to avoid
              unnecessary wakeups, thereby optimizing power consumption.

              If enabled in the kernel (CONFIG_TIMER_STATS), but not used,  it
              has  almost  zero  runtime overhead and a relatively small data-
              structure overhead.  Even if collection is enabled  at  runtime,
              overhead  is  low:  all  the  locking  is  per-CPU and lookup is
              hashed.

              The /proc/timer_stats file is  used  both  to  control  sampling
              facility and to read out the sampled information.

              The timer_stats functionality is inactive on bootup.  A sampling
              period can be started using the following command:

                  # echo 1 > /proc/timer_stats

              The following command stops a sampling period:

                  # echo 0 > /proc/timer_stats

              The statistics can be retrieved by:

                  $ cat /proc/timer_stats

              While sampling is enabled, each readout  from  /proc/timer_stats
              will  see  newly updated statistics.  Once sampling is disabled,
              the sampled information is kept until a  new  sample  period  is
              started.  This allows multiple readouts.

              Sample output from /proc/timer_stats:

   $ cat /proc/timer_stats
   Timer Stats Version: v0.3
   Sample period: 1.764 s
   Collection: active
     255,     0 swapper/3        hrtimer_start_range_ns (tick_sched_timer)
      71,     0 swapper/1        hrtimer_start_range_ns (tick_sched_timer)
      58,     0 swapper/0        hrtimer_start_range_ns (tick_sched_timer)
       4,  1694 gnome-shell      mod_delayed_work_on (delayed_work_timer_fn)
      17,     7 rcu_sched        rcu_gp_kthread (process_timeout)
   ...
       1,  4911 kworker/u16:0    mod_delayed_work_on (delayed_work_timer_fn)
      1D,  2522 kworker/0:0      queue_delayed_work_on (delayed_work_timer_fn)
   1029 total events, 583.333 events/sec

              The output columns are:

              *  a  count  of  the  number  of events, optionally (since Linux
                 2.6.23) followed by the letter 'D' if this  is  a  deferrable
                 timer;

              *  the PID of the process that initialized the timer;

              *  the name of the process that initialized the timer;

              *  the function where the timer was initialized; and

              *  (in  parentheses)  the  callback  function that is associated
                 with the timer.

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

       /proc/version
              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
              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 use-
              ful for analyzing virtual memory behavior.

NOTES
       Many strings (i.e., the environment and command line) are in the inter-
       nal  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), namespaces(7),
       time(7), arp(8), hdparm(8), ifconfig(8), init(8),  lsmod(8),  lspci(8),
       mount(8), netstat(8), procinfo(8), route(8), sysctl(8)

       The Linux kernel source files: Documentation/filesystems/proc.txt Docu-
       mentation/sysctl/fs.txt,  Documentation/sysctl/kernel.txt,   Documenta-
       tion/sysctl/net.txt, and Documentation/sysctl/vm.txt.

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

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