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.   Typi-
       cally,  it  is  mounted automatically by the system, but it can also be
       mounted manually using a command such as:

           mount -t proc proc /proc

       Most of the files in the proc filesystem are read-only, but some  files
       are writable, allowing kernel variables to be changed.

   Mount options
       The proc filesystem supports the following mount options:

       hidepid=n (since Linux 3.3)
              This   option   controls  who  can  access  the  information  in
              /proc/[pid] directories.  The argument, n, is one of the follow-
              ing values:

              0   Everybody  may  access all /proc/[pid] directories.  This is
                  the traditional behavior, and the default if this mount  op-
                  tion is not specified.

              1   Users  may  not  access  files and subdirectories inside any
                  /proc/[pid] directories but their own (the  /proc/[pid]  di-
                  rectories  themselves remain visible).  Sensitive files such
                  as /proc/[pid]/cmdline and /proc/[pid]/status are  now  pro-
                  tected  against  other  users.   This makes it impossible to
                  learn whether any user is running  a  specific  program  (so
                  long  as  the program doesn't otherwise reveal itself by its
                  behavior).

              2   As for mode 1, but in addition the  /proc/[pid]  directories
                  belonging  to other users become invisible.  This means that
                  /proc/[pid] entries can no longer be used  to  discover  the
                  PIDs  on  the  system.   This  doesn't  hide the fact that a
                  process with a specific PID value exists (it can be  learned
                  by  other  means,  for  example,  by "kill -0 $PID"), but it
                  hides a process's UID and  GID,  which  could  otherwise  be
                  learned  by  employing  stat(2)  on a /proc/[pid] directory.
                  This greatly complicates an attacker's task of gathering in-
                  formation about running processes (e.g., discovering whether
                  some daemon is running with elevated privileges, whether an-
                  other  user is running some sensitive program, whether other
                  users are running any program at all, and so on).

       gid=gid (since Linux 3.3)
              Specifies the ID of a group  whose  members  are  authorized  to
              learn process information otherwise prohibited by hidepid (i.e.,
              users in this group behave as  though  /proc  was  mounted  with
              hidepid=0).   This  group  should  be used instead of approaches
              such as putting nonroot users into the sudoers(5) file.

   Files and directories
       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 /proc/[pid] subdirectory contains the pseudo-files and  di-
              rectories  described  below.   These files are normally owned by
              the effective user and effective group ID of the process.   How-
              ever,  as a security measure, the ownership is made root:root if
              the process's "dumpable" attribute is set to a value other  than
              1.  This attribute may change for the following reasons:

              *  The   attribute   was   explicitly   set   via  the  prctl(2)
                 PR_SET_DUMPABLE operation.

              *  The  attribute  was  reset  to  the   value   in   the   file
                 /proc/sys/fs/suid_dumpable (described below), for the reasons
                 described in prctl(2).

              Resetting the "dumpable" attribute to 1 reverts the ownership of
              the /proc/[pid]/* files to the process's real UID and real GID.

       /proc/[pid]/attr
              The files in this directory provide an API for security modules.
              The contents of this directory are files that can  be  read  and
              written  in  order to set security-related attributes.  This di-
              rectory was added to support SELinux, but the intention was that
              the  API  be  general  enough to support other security modules.
              For the purpose of explanation, examples  of  how  SELinux  uses
              these files are provided below.

              This directory is present only if the kernel was configured with
              CONFIG_SECURITY.

       /proc/[pid]/attr/current (since Linux 2.6.0)
              The contents of this file represent  the  current  security  at-
              tributes of the process.

              In  SELinux,  this file is used to get the security context of a
              process.  Prior to Linux 2.6.11, this file could not be used  to
              set  the  security  context  (a  write was always denied), since
              SELinux limited process security transitions to  execve(2)  (see
              the  description  of /proc/[pid]/attr/exec, below).  Since Linux
              2.6.11, SELinux lifted this  restriction  and  began  supporting
              "set"  operations  via writes to this node if authorized by pol-
              icy, although use of this operation is only suitable for  appli-
              cations  that are trusted to maintain any desired separation be-
              tween the old and new security contexts.  Prior to Linux 2.6.28,
              SELinux did not allow threads within a multi-threaded process to
              set their security context via this node as it  would  yield  an
              inconsistency among the security contexts of the threads sharing
              the same memory space.  Since Linux 2.6.28, SELinux lifted  this
              restriction  and  began  supporting "set" operations for threads
              within a multithreaded process if the new  security  context  is
              bounded  by the old security context, where the bounded relation
              is defined in policy and guarantees that the new  security  con-
              text  has  a  subset of the permissions of the old security con-
              text.  Other security modules may choose to support "set" opera-
              tions via writes to this node.

       /proc/[pid]/attr/exec (since Linux 2.6.0)
              This  file  represents  the  attributes to assign to the process
              upon a subsequent execve(2).

              In SELinux, this is needed to support  role/domain  transitions,
              and  execve(2)  is  the preferred point to make such transitions
              because it offers better control over the initialization of  the
              process  in the new security label and the inheritance of state.
              In SELinux, this attribute is reset on execve(2) so that the new
              program  reverts to the default behavior for any execve(2) calls
              that it may make.  In SELinux, a process can set  only  its  own
              /proc/[pid]/attr/exec attribute.

       /proc/[pid]/attr/fscreate (since Linux 2.6.0)
              This  file  represents the attributes to assign to files created
              by  subsequent  calls  to  open(2),  mkdir(2),  symlink(2),  and
              mknod(2)

              SELinux  employs  this file to support creation of a file (using
              the aforementioned system calls) in  a  secure  state,  so  that
              there  is no risk of inappropriate access being obtained between
              the time of creation and the time that attributes are  set.   In
              SELinux,  this  attribute is reset on execve(2), so that the new
              program reverts to the default behavior for  any  file  creation
              calls  it may make, but the attribute will persist across multi-
              ple file creation calls within a program unless it is explicitly
              reset.    In   SELinux,   a   process   can  set  only  its  own
              /proc/[pid]/attr/fscreate attribute.

       /proc/[pid]/attr/keycreate (since Linux 2.6.18)
              If a process writes a security context into this file, all  sub-
              sequently  created  keys  (add_key(2)) will be labeled with this
              context.  For further information, see the  kernel  source  file
              Documentation/security/keys/core.rst  (or file Documentation/se-
              curity/keys.txt on Linux between 3.0  and  4.13,  or  Documenta-
              tion/keys.txt before Linux 3.0).

       /proc/[pid]/attr/prev (since Linux 2.6.0)
              This  file  contains  the security context of the process before
              the  last  execve(2);   that   is,   the   previous   value   of
              /proc/[pid]/attr/current.

       /proc/[pid]/attr/socketcreate (since Linux 2.6.18)
              If  a process writes a security context into this file, all sub-
              sequently created sockets will be labeled with this context.

       /proc/[pid]/autogroup (since Linux 2.6.38)
              See sched(7).

       /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).

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /proc/[pid]/cgroup (since Linux 2.6.24)
              See cgroups(7).

       /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 us-
              ing.  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 in-
              terval, 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.

              Further values can be written to affect different properties:

              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.

              5 (since Linux 4.0)
                     Reset the peak resident set size ("high water  mark")  to
                     the process's current resident set size value.

              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)).

              Permission to dereference or read  (readlink(2))  this  symbolic
              link  is  governed  by a ptrace access mode PTRACE_MODE_READ_FS-
              CREDS check; see ptrace(2).

       /proc/[pid]/environ
              This file contains the initial environment that was set when the
              currently  executing program was started via execve(2).  The en-
              tries 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

              If, after an execve(2), the  process  modifies  its  environment
              (e.g.,  by  calling functions such as putenv(3) or modifying the
              environ(7) variable directly), this file will not reflect  those
              changes.

              Furthermore,  a process may change the memory location that this
              file refers via prctl(2) operations such as PR_SET_MM_ENV_START.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /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 that is being run by process
              [pid].  If the pathname has been  unlinked,  the  symbolic  link
              will  contain  the  string  '(deleted)' appended to the original
              pathname.  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)).

              Permission to dereference or read  (readlink(2))  this  symbolic
              link  is  governed  by a ptrace access mode PTRACE_MODE_READ_FS-
              CREDS check; see ptrace(2).

              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 in-
              formation in one of the files under /proc/net/.

              For file descriptors that have  no  corresponding  inode  (e.g.,
              file    descriptors   produced   by   bpf(2),   epoll_create(2),
              eventfd(2),  inotify_init(2),  perf_event_open(2),  signalfd(2),
              timerfd_create(2), and userfaultfd(2)), the entry will be a sym-
              bolic link with contents of the form

                  anon_inode:<file-type>

              In many cases (but not all),  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 take a filename as a  command-line  argument,  but
              don't take input from standard input if no argument is supplied,
              and programs that write to a file named as a command-line  argu-
              ment, but don't send their output to standard output if no argu-
              ment is supplied, can nevertheless be made to use standard input
              or standard output by using /proc/[pid]/fd files as command-line
              arguments.  For example, assuming that -i is the flag  designat-
              ing 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 ...

              Permission to dereference or  read  (readlink(2))  the  symbolic
              links  in  this  directory  is  governed by a ptrace access mode
              PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

              Note that for file descriptors referring to  inodes  (pipes  and
              sockets, see above), those inodes still have permission bits and
              ownership information distinct from those of the  /proc/[pid]/fd
              entry, and that the owner may differ from the user and group IDs
              of the process.  An unprivileged process may lack permissions to
              open them, as in this example:

                  $ echo test | sudo -u nobody cat
                  test
                  $ echo test | sudo -u nobody cat /proc/self/fd/0
                  cat: /proc/self/fd/0: Permission denied

              File  descriptor  0  refers to the pipe created by the shell and
              owned by that shell's user, which is not nobody, so cat does not
              have  permission  to  create  a new file descriptor to read from
              that inode, even though it can still read from its existing file
              descriptor 0.

       /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  files
              in this directory are readable only by the owner of the process.
              The contents of each file can  be  read  to  obtain  information
              about the corresponding file descriptor.  The content depends on
              the type of file referred to by the corresponding file  descrip-
              tor.

              For regular files and directories, we see something like:

                  $ cat /proc/12015/fdinfo/4
                  pos:    1000
                  flags:  01002002
                  mnt_id: 21

              The fields are as follows:

              pos    This is a decimal number showing the file offset.

              flags  This  is  an  octal  number that displays the file access
                     mode and file status flags (see open(2)).  If the  close-
                     on-exec file descriptor flag is set, then flags will also
                     include the value O_CLOEXEC.

                     Before Linux 3.1, this field  incorrectly  displayed  the
                     setting  of  O_CLOEXEC  at  the time the file was opened,
                     rather than the  current  setting  of  the  close-on-exec
                     flag.

              mnt_id This  field,  present  since Linux 3.15, is the ID of the
                     mount point containing this file.  See the description of
                     /proc/[pid]/mountinfo.

              For  eventfd  file  descriptors  (see eventfd(2)), we see (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   10
                  eventfd-count:               40

              eventfd-count is the current value of the  eventfd  counter,  in
              hexadecimal.

              For  epoll  file descriptors (see epoll(7)), we see (since Linux
              3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   10
                  tfd:        9 events:       19 data: 74253d2500000009
                  tfd:        7 events:       19 data: 74253d2500000007

              Each of the lines beginning tfd describes one of  the  file  de-
              scriptors  being  monitored  via  the epoll file descriptor (see
              epoll_ctl(2) for some details).  The tfd field is the number  of
              the  file descriptor.  The events field is a hexadecimal mask of
              the events being monitored for this file descriptor.   The  data
              field is the data value associated with this file descriptor.

              For  signalfd  file descriptors (see signalfd(2)), we see (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   10
                  sigmask:  0000000000000006

              sigmask is the hexadecimal mask of signals that are accepted via
              this  signalfd  file descriptor.  (In this example, bits 2 and 3
              are set, corresponding to the signals SIGINT  and  SIGQUIT;  see
              signal(7).)

              For  inotify  file  descriptors  (see inotify(7)), we see (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    00
                  mnt_id:   11
                  inotify wd:2 ino:7ef82a sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:2af87e00220ffd73
                  inotify wd:1 ino:192627 sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:27261900802dfd73

              Each of the lines beginning with "inotify" displays  information
              about one file or directory that is being monitored.  The fields
              in this line are as follows:

              wd     A watch descriptor number (in decimal).

              ino    The inode number of the target file (in hexadecimal).

              sdev   The ID of the device where the target  file  resides  (in
                     hexadecimal).

              mask   The  mask  of  events being monitored for the target file
                     (in hexadecimal).

              If the kernel was built with exportfs support, the path  to  the
              target  file  is exposed as a file handle, via three hexadecimal
              fields: fhandle-bytes, fhandle-type, and f_handle.

              For fanotify file descriptors (see fanotify(7)), we  see  (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   11
                  fanotify flags:0 event-flags:88002
                  fanotify ino:19264f sdev:800001 mflags:0 mask:1 ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:4f261900a82dfd73

              The  fourth  line displays information defined when the fanotify
              group was created via fanotify_init(2):

              flags  The flags argument given to  fanotify_init(2)  (expressed
                     in hexadecimal).

              event-flags
                     The event_f_flags argument given to fanotify_init(2) (ex-
                     pressed in hexadecimal).

              Each additional line shown  in  the  file  contains  information
              about  one  of  the  marks in the fanotify group.  Most of these
              fields are as for inotify, except:

              mflags The flags associated with the mark (expressed in hexadec-
                     imal).

              mask   The events mask for this mark (expressed in hexadecimal).

              ignored_mask
                     The  mask  of  events that are ignored for this mark (ex-
                     pressed in hexadecimal).

              For details on these fields, see fanotify_mark(2).

       /proc/[pid]/gid_map (since Linux 3.5)
              See user_namespaces(7).

       /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.

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /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 di-
              rectory.  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.  Privilege  (CAP_SYS_AD-
              MIN) is required to view the contents of this directory.

       /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.

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

              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.  See
                          vdso(7).

                   [heap] The process's heap.

              If the pathname field is blank, this is an anonymous mapping  as
              obtained  via  mmap(2).  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).

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /proc/[pid]/mountinfo (since Linux 2.6.26)
              This  file  contains  information  about  mount  points  in  the
              process's mount namespace (see  mount_namespaces(7)).   It  sup-
              plies  various  information  (e.g.,  propagation  state, root of
              mount for bind mounts, identifier for each mount and its parent)
              that  is  missing  from the (older) /proc/[pid]/mounts file, and
              fixes various other problems with that file  (e.g.,  nonextensi-
              bility,  failure  to distinguish per-mount versus per-superblock
              options).

              The file 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  be-
              low:

              (1)  mount  ID:  a  unique ID for the mount (may be reused after
                   umount(2)).

              (2)  parent ID: the ID of the parent mount (or of self  for  the
                   root of this mount namespace's mount tree).

                   If  the  parent mount point lies outside the process's root
                   directory (see chroot(2)), the ID shown here won't  have  a
                   corresponding  record in mountinfo whose mount ID (field 1)
                   matches this parent mount ID (because mount points that lie
                   outside  the  process's  root  directory  are  not shown in
                   mountinfo).  As a special case of this point, the process's
                   root mount point may have a parent mount (for the initramfs
                   filesystem) that lies outside the process's root directory,
                   and  an  entry  for  that  mount  point  will not appear in
                   mountinfo.

              (3)  major:minor: the value of st_dev for files on this filesys-
                   tem (see stat(2)).

              (4)  root: the pathname of the directory in the filesystem which
                   forms the root of this mount.

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

              (6)  mount options: per-mount options.

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

              (8)  separator: the end of the optional fields is  marked  by  a
                   single hyphen.

              (9)  filesystem   type:   the   filesystem   type  in  the  form
                   "type[.subtype]".

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

              (11) super options: per-superblock options.

              Currently, the possible  optional  fields  are  shared,  master,
              propagate_from,  and  unbindable.  See mount_namespaces(7) for a
              description of these fields.  Parsers should ignore all unrecog-
              nized optional fields.

              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  file  lists  all  the filesystems currently mounted in the
              process's mount namespace (see mount_namespaces(7)).  The format
              of this file is documented in fstab(5).

              Since  kernel version 2.6.15, this file is pollable: after open-
              ing the file for  reading,  a  change  in  this  file  (i.e.,  a
              filesystem  mount  or unmount) causes select(2) to mark the file
              descriptor as having an exceptional condition, and  poll(2)  and
              epoll_wait(2)  mark  the  file as having a priority event (POLL-
              PRI).  (Before Linux 2.6.30, a change in this file was indicated
              by  the  file descriptor being marked as readable for select(2),
              and being marked as having an error condition  for  poll(2)  and
              epoll_wait(2).)

       /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
              (see mount_namespaces(7)).  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.

       /proc/[pid]/net (since Linux 2.6.25)
              See the description of /proc/net.

       /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  al-
              together for this process.  A positive score increases the like-
              lihood of this process being killed by the OOM-killer;  a  nega-
              tive 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  de-
              creases (-) for factors including:

              * whether the process is privileged (-).

              Before kernel 2.6.36 the following factors were also used in the
              calculation of oom_score:

              * 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) (+); 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  ex-
              hausted,  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  al-
              lowed 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  an
              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 al-
              lowed 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.

                   60-57 (since Linux 3.11)
                          Zero

                   56 (since Linux 4.2)
                          The page is exclusively mapped.

                   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.

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /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.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /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/*.

              Note however that this file is not merely a symbolic  link.   It
              provides  the  same view of the filesystem (including namespaces
              and the set of per-process mounts) as the  process  itself.   An
              example  illustrates  this  point.   In one terminal, we start a
              shell in new user and mount namespaces, and  in  that  shell  we
              create some new mount points:

                  $ PS1='sh1# ' unshare -Urnm
                  sh1# mount -t tmpfs tmpfs /etc  # Mount empty tmpfs at /etc
                  sh1# mount --bind /usr /dev     # Mount /usr at /dev
                  sh1# echo $$
                  27123

              In  a second terminal window, in the initial mount namespace, we
              look at the contents of the corresponding mounts in the  initial
              and new namespaces:

                  $ PS1='sh2# ' sudo sh
                  sh2# ls /etc | wc -l                  # In initial NS
                  309
                  sh2# ls /proc/27123/root/etc | wc -l  # /etc in other NS
                  0                                     # The empty tmpfs dir
                  sh2# ls /dev | wc -l                  # In initial NS
                  205
                  sh2# ls /proc/27123/root/dev | wc -l  # /dev in other NS
                  11                                    # Actually bind
                                                        # mounted to /usr
                  sh2# ls /usr | wc -l                  # /usr in initial NS
                  11

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

              Permission  to  dereference  or read (readlink(2)) this symbolic
              link is governed by a ptrace  access  mode  PTRACE_MODE_READ_FS-
              CREDS check; see ptrace(2).

       /proc/[pid]/seccomp (Linux 2.6.12 to 2.6.22)
              This  file  can  be used to read and change the process's secure
              computing (seccomp) mode setting.  It contains the  value  0  if
              the  process  is not in seccomp mode, and 1 if the process is in
              strict seccomp mode (see seccomp(2)).  Writing 1  to  this  file
              places  the  process irreversibly in strict seccomp mode.  (Fur-
              ther attempts to write to the file fail with the EPERM error.)

              In Linux 2.6.23, this file went away,  to  be  replaced  by  the
              prctl(2) PR_GET_SECCOMP and PR_SET_SECCOMP operations (and later
              by seccomp(2) and the Seccomp field in /proc/[pid]/status).

       /proc/[pid]/setgroups (since Linux 3.19)
              See user_namespaces(7).

       /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
                  ShmemHugePages:        0 kB
                  ShmemPmdMapped:        0 kB
                  Swap:                  0 kB
                  KernelPageSize:        4 kB
                  MMUPageSize:           4 kB
                  KernelPageSize:        4 kB
                  MMUPageSize:           4 kB
                  Locked:                0 kB
                  ProtectionKey:         0
                  VmFlags: rd ex mr mw me dw

              The  first  of these lines shows the same information as is dis-
              played for the mapping in /proc/[pid]/maps.  The following lines
              show  the size of the mapping, the amount of the mapping that is
              currently resident in RAM ("Rss"),  the  process's  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" line (available since Linux 2.6.29) is the
              page size used by the kernel to back the  virtual  memory  area.
              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  64kB  as a base page size may still use 4kB pages
              for the MMU on older processors.  To  distinguish  the  two  at-
              tributes,  the  "MMUPageSize"  line  (also available since Linux
              2.6.29) reports the page size used by the MMU.

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

              The  "ProtectionKey"  line  (available  since  Linux 4.9, on x86
              only) contains the memory protection key (see pkeys(7))  associ-
              ated  with  the virtual memory area.  This entry is present only
              if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTEC-
              TION_KEYS configuration option.

              The  "VmFlags"  line  (available since Linux 3.8) represents the
              kernel flags associated with the virtual  memory  area,  encoded
              using the following two-letter codes:

                  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

              "ProtectionKey"  field  contains  the memory protection key (see
              pkeys(5)) associated with the virtual memory area.  Present only
              if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTEC-
              TION_KEYS configuration option. (since Linux 4.6)

              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 op-
              tion.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /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 listed below.  Whether or not certain of these fields
              display valid information is governed by a  ptrace  access  mode
              PTRACE_MODE_READ_FSCREDS | PTRACE_MODE_NOAUDIT  check  (refer to
              ptrace(2)).  If the check denies access, then the field value is
              displayed  as  0.   The  affected  fields are indicated with the
              marking [PT].

              (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.

              (10) 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  be-
                        low),  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  to-
                        ward  text,  data,  or stack space.  This does not in-
                        clude 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  [PT]
                        The address above which program text can run.

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

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

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

              (30) kstkeip  %lu  [PT]
                        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  [PT]
                        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)  [PT]
                        Address above which program initialized and uninitial-
                        ized (BSS) data are placed.

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

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

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

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

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

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

              (52) exit_code  %d  (since Linux 3.5)  [PT]
                        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)
                  shared     (3) number of resident shared pages (i.e., backed by a file)
                             (same as RssFile+RssShmem in /proc/[pid]/status)
                  text       (4) text (code)
                  lib        (5) library (unused since Linux 2.6; always 0)
                  data       (6) data + stack
                  dt         (7) dirty pages (unused since Linux 2.6; always 0)

       /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
                  Umask:  0022
                  State:  S (sleeping)
                  Tgid:   17248
                  Ngid:   0
                  Pid:    17248
                  PPid:   17200
                  TracerPid:      0
                  Uid:    1000    1000    1000    1000
                  Gid:    100     100     100     100
                  FDSize: 256
                  Groups: 16 33 100
                  NStgid: 17248
                  NSpid:  17248
                  NSpgid: 17248
                  NSsid:  17200
                  VmPeak:     131168 kB
                  VmSize:     131168 kB
                  VmLck:           0 kB
                  VmPin:           0 kB
                  VmHWM:       13484 kB
                  VmRSS:       13484 kB
                  RssAnon:     10264 kB
                  RssFile:      3220 kB
                  RssShmem:        0 kB
                  VmData:      10332 kB
                  VmStk:         136 kB
                  VmExe:         992 kB
                  VmLib:        2104 kB
                  VmPTE:          76 kB
                  VmPMD:          12 kB
                  VmSwap:          0 kB
                  HugetlbPages:          0 kB        # 4.4
                  Threads:        1
                  SigQ:   0/3067
                  SigPnd: 0000000000000000
                  ShdPnd: 0000000000000000
                  SigBlk: 0000000000010000
                  SigIgn: 0000000000384004
                  SigCgt: 000000004b813efb
                  CapInh: 0000000000000000
                  CapPrm: 0000000000000000
                  CapEff: 0000000000000000
                  CapBnd: ffffffffffffffff
                  CapAmb:   0000000000000000
                  NoNewPrivs:     0
                  Seccomp:        0
                  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.

              * Umask:  Process umask, expressed in octal with a leading zero;
                see umask(2).  (Since Linux 4.7.)

              * 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).

              * Ngid: NUMA group ID (0 if none; since Linux 3.13).

              * 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.

              * NStgid : Thread group ID (i.e., PID) in each of the PID  name-
                spaces  of  which [pid] is a member.  The leftmost entry shows
                the value with respect to the PID  namespace  of  the  reading
                process,  followed  by  the value in successively nested inner
                namespaces.  (Since Linux 4.1.)

              * NSpid: Thread ID in each of the PID namespaces of which  [pid]
                is  a  member.   The fields are ordered as for NStgid.  (Since
                Linux 4.1.)

              * NSpgid: Process group ID in each  of  the  PID  namespaces  of
                which  [pid]  is a member.  The fields are ordered as for NSt-
                gid.  (Since Linux 4.1.)

              * NSsid: descendant namespace session ID hierarchy Session ID in
                each  of  the  PID namespaces of which [pid] is a member.  The
                fields are ordered as for NStgid.  (Since Linux 4.1.)

              * VmPeak: Peak virtual memory size.

              * VmSize: Virtual memory size.

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

              * VmPin: Pinned memory size (since Linux 3.2).  These are  pages
                that can't be moved because something needs to directly access
                physical memory.

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

              * VmRSS: Resident set size.  Note that the value here is the sum
                of RssAnon, RssFile, and RssShmem.

              * RssAnon:  Size  of  resident  anonymous  memory.  (since Linux
                4.5).

              * RssFile: Size of resident file mappings.  (since Linux 4.5).

              * RssShmem: Size of resident shared memory  (includes  System  V
                shared  memory,  mappings  from tmpfs(5), and shared anonymous
                mappings).  (since Linux 4.5).

              * 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).

              * VmPMD: Size of second-level page tables (since Linux 4.0).

              * VmSwap: Swapped-out virtual memory size by  anonymous  private
                pages; shmem swap usage is not included (since Linux 2.6.34).

              * HugetlbPages:  Size  of hugetlb memory portions.  (since Linux
                4.4).

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

              * SigQ: This field contains two slash-separated numbers that re-
                late  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  de-
                scription 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 in-
                heritable,  permitted,  and  effective  sets  (see   capabili-
                ties(7)).

              * CapBnd: Capability Bounding set (since Linux 2.6.26, see capa-
                bilities(7)).

              * CapAmb: Ambient capability set (since Linux 4.3, see capabili-
                ties(7)).

              * NoNewPrivs:  Value  of the no_new_privs bit (since Linux 4.10,
                see prctl(2)).

              * Seccomp: Seccomp mode of the process  (since  Linux  3.8,  see
                seccomp(2)).   0  means  SECCOMP_MODE_DISABLED;  1  means SEC-
                COMP_MODE_STRICT; 2 means SECCOMP_MODE_FILTER.  This field  is
                provided  only if the kernel was built with the CONFIG_SECCOMP
                kernel configuration option enabled.

              * 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 ex-
              posed, 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 the file contains just the string
              "running".

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

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /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 nu-
              merical thread ID ([tid]) of the thread (see gettid(2)).  Within
              each  of  these subdirectories, there is a set of files with the
              same names and contents as under  the  /proc/[pid]  directories.
              For  attributes that are shared by all threads, the contents for
              each of the files under the task/[tid]  subdirectories  will  be
              the  same as in the corresponding file in the parent /proc/[pid]
              directory  (e.g.,  in  a  multithreaded  process,  all  of   the
              task/[tid]/cwd   files   will   have   the  same  value  as  the
              /proc/[pid]/cwd file in the parent directory, since all  of  the
              threads in a process share a working directory).  For attributes
              that are distinct for each thread, the corresponding files under
              task/[tid]  may  have  different values (e.g., various fields in
              each of the task/[tid]/status files may be  different  for  each
              thread),  or  they  might not exist in /proc/[pid] at all.  In a
              multithreaded process, the contents of the /proc/[pid]/task  di-
              rectory  are not available if the main thread has already termi-
              nated (typically by calling pthread_exit(3)).

       /proc/[pid]/task/[tid]/children (since Linux 3.5)
              A space-separated list of child tasks of this task.  Each  child
              task is represented by its TID.

              This option is intended for use by the checkpoint-restore (CRIU)
              system, and reliably provides a list of children only if all  of
              the  child  processes  are  stopped or frozen.  It does not work
              properly if children of the target task exit while the  file  is
              being  read!  Exiting children may cause non-exiting children to
              be omitted from the list.  This makes this interface  even  more
              unreliable  than  classic  PID-based approaches if the inspected
              task and its children aren't frozen, and most code should proba-
              bly not use this interface.

              Until  Linux  4.2, the presence of this file was governed by the
              CONFIG_CHECKPOINT_RESTORE kernel  configuration  option.   Since
              Linux 4.2, it is governed by the CONFIG_PROC_CHILDREN option.

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

                  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 value supplied to the signal handler.   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  (or the kernel thread ID of the thread)
                     that will be delivered a signal if the timer delivers no-
                     tifications 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.

              This  file is available only when the kernel was configured with
              CONFIG_CHECKPOINT_RESTORE.

       /proc/[pid]/timerslack_ns (since Linux 4.6)
              This file exposes the process's "current" timer slack value, ex-
              pressed  in  nanoseconds.   The  file  is writable, allowing the
              process's timer slack value to be changed.  Writing  0  to  this
              file  resets  the  "current"  timer slack to the "default" timer
              slack  value.   For  further  details,  see  the  discussion  of
              PR_SET_TIMERSLACK in prctl(2).

              Initially,  permission  to  access  this  file was governed by a
              ptrace  access  mode   PTRACE_MODE_ATTACH_FSCREDS   check   (see
              ptrace(2)).   However, this was subsequently deemed too strict a
              requirement (and had the side effect that requiring a process to
              have  the  CAP_SYS_PTRACE capability would also allow it to view
              and change any process's memory).  Therefore, since  Linux  4.9,
              only  the (weaker) CAP_SYS_NICE capability is required to access
              this file.

       /proc/[pid]/uid_map, /proc/[pid]/gid_map (since Linux 3.5)
              See user_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.

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /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
              formula:

                  (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 an 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-
              bytes, 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 fragmented, the counters for higher or-
              der 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/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/cgroups (since Linux 2.6.24)
              See cgroups(7).

       /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/crypto
              A list of the ciphers provided by the kernel  crypto  API.   For
              details,  see  the  kernel Linux Kernel Crypto API documentation
              available  under  the   kernel   source   directory   Documenta-
              tion/crypto/ (or Documentation/DocBook before 4.10; the documen-
              tation can be built using a command such as make htmldocs in the
              root directory of the kernel source tree).

       /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 bo-
              gomips; a system constant that is calculated during kernel  ini-
              tialization.   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 in-
              clude:

                  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 4 KiB.

       /proc/keys (since Linux 2.6.10)
              See keyrings(7).

       /proc/key-users (since Linux 2.6.10)
              See keyrings(7).

       /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/kpagecgroup (since Linux 4.3)
              This  file  contains  a 64-bit inode number of the memory cgroup
              each page is charged to, indexed by page frame number  (see  the
              discussion of /proc/[pid]/pagemap).

              The  /proc/kpagecgroup  file is present only if the CONFIG_MEMCG
              kernel configuration option is enabled.

       /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)
                  17 - 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)
                  23 - KPF_BALLOON        (since Linux 3.18)
                  24 - KPF_ZERO_PAGE      (since Linux 4.0)
                  25 - KPF_IDLE           (since Linux 4.3)

              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 en-
              tities  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)).

              An example of the content shown in this file is the following:

                  1: POSIX  ADVISORY  READ  5433 08:01:7864448 128 128
                  2: FLOCK  ADVISORY  WRITE 2001 08:01:7864554 0 EOF
                  3: FLOCK  ADVISORY  WRITE 1568 00:2f:32388 0 EOF
                  4: POSIX  ADVISORY  WRITE 699 00:16:28457 0 EOF
                  5: POSIX  ADVISORY  WRITE 764 00:16:21448 0 0
                  6: POSIX  ADVISORY  READ  3548 08:01:7867240 1 1
                  7: POSIX  ADVISORY  READ  3548 08:01:7865567 1826 2335
                  8: OFDLCK ADVISORY  WRITE -1 08:01:8713209 128 191

              The fields shown in each line are as follows:

              (1) The ordinal position of the lock in the list.

              (2) The lock type.  Values that may appear here include:

                  FLOCK  This is a BSD file lock created using flock(2).

                  OFDLCK This is an open file description (OFD)  lock  created
                         using fcntl(2).

                  POSIX  This  is  a  POSIX  byte-range lock created using fc-
                         ntl(2).

              (3) Among the strings that can appear here are the following:

                  ADVISORY
                         This is an advisory lock.

                  MANDATORY
                         This is a mandatory lock.

              (4) The type of lock.  Values that can appear here are:

                  READ   This is a POSIX or OFD read lock,  or  a  BSD  shared
                         lock.

                  WRITE  This is a POSIX or OFD write lock, or a BSD exclusive
                         lock.

              (5) The PID of the process that owns the lock.

                  Because OFD locks are not owned by a single  process  (since
                  multiple  processes  may have file descriptors that refer to
                  the same open file description), the value -1  is  displayed
                  in  this  field  for  OFD locks.  (Before kernel 4.14, a bug
                  meant that the PID of the process  that  initially  acquired
                  the lock was displayed instead of the value -1.)

              (6) Three  colon-separated subfields that identify the major and
                  minor device ID of  the  device  containing  the  filesystem
                  where  the locked file resides, followed by the inode number
                  of the locked file.

              (7) The byte offset of the first byte  of  the  lock.   For  BSD
                  locks, this value is always 0.

              (8) The  byte  offset of the last byte of the lock.  EOF in this
                  field means that the lock extends to the end  of  the  file.
                  For BSD locks, the value shown is always EOF.

              Since  Linux 4.9, the list of locks shown in /proc/locks is fil-
              tered to show just the locks for the processes in the PID  name-
              space (see pid_namespaces(7)) for which the /proc filesystem was
              mounted.  (In the initial PID namespace, there is  no  filtering
              of the records shown in this file.)

              The  lslocks(8)  command  provides  a bit more information about
              each lock.

       /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 be-
              low,  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.

              MemAvailable %lu (since Linux 3.14)
                     An  estimate of how much memory is available for starting
                     new applications, without swapping.

              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  be-
                     cause  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 el-
                     igible 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)
                     Amount of memory consumed in tmpfs(5) filesystems.

              Slab %lu
                     In-kernel data structures cache.  (See slabinfo(5).)

              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 de-
                     scribed 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 /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.

              ShmemHugePages %lu (since Linux 4.8)
                     (CONFIG_TRANSPARENT_HUGEPAGE  is  required.)  Memory used
                     by shared memory (shmem) and tmpfs(5) allocated with huge
                     pages

              ShmemPmdMapped %lu (since Linux 4.8)
                     (CONFIG_TRANSPARENT_HUGEPAGE is required.)  Shared memory
                     mapped into user space with huge pages.

              CmaTotal %lu (since Linux 3.1)
                     Total CMA (Contiguous  Memory  Allocator)  pages.   (CON-
                     FIG_CMA is required.)

              CmaFree %lu (since Linux 3.1)
                     Free  CMA  (Contiguous  Memory  Allocator)  pages.  (CON-
                     FIG_CMA is required.)

              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.

              DirectMap4k %lu (since Linux 2.6.27)
                     Number of bytes of RAM linearly mapped by kernel  in  4kB
                     pages.  (x86.)

              DirectMap4M %lu (since Linux 2.6.27)
                     Number  of  bytes of RAM linearly mapped by kernel in 4MB
                     pages.  (x86 with  CONFIG_X86_64  or  CONFIG_X86_PAE  en-
                     abled.)

              DirectMap2M %lu (since Linux 2.6.27)
                     Number  of  bytes of RAM linearly mapped by kernel in 2MB
                     pages.   (x86  with  neither   CONFIG_X86_64   nor   CON-
                     FIG_X86_PAE enabled.)

              DirectMap1G %lu (since Linux 2.6.27)
                     (x86 with CONFIG_X86_64 and CONFIG_X86_DIRECT_GBPAGES en-
                     abled.)

       /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 (see mount_name-
              spaces(7)), this file became a link to /proc/self/mounts,  which
              lists  the  mount  points  of the process's own mount namespace.
              The format of this file is documented in fstab(5).

       /proc/mtrr
              Memory Type Range Registers.  See the Linux kernel  source  file
              Documentation/x86/mtrr.txt   (or  Documentation/mtrr.txt  before
              Linux 2.6.28) for details.

       /proc/net
              This directory contains various files  and  subdirectories  con-
              taining  information about the networking layer.  The files con-
              tain ASCII structures and are, therefore, readable with  cat(1).
              However, the standard netstat(8) suite provides much cleaner ac-
              cess to these files.

              With the advent of network namespaces, various  information  re-
              lating  to the network stack is virtualized (see namespaces(7)).
              Thus, since Linux 2.6.25, /proc/net is a symbolic  link  to  the
              directory  /proc/self/net, which contains the same files and di-
              rectories as listed below.  However, these files and directories
              now  expose  information  for the network namespace of which the
              process is a member.

       /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 us-
              age.  The "tr", "tm->when", and "rexmits" fields  hold  internal
              information  of  the kernel socket state and are useful only 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 us-
              age.  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

              The fields are as follows:

              Num:      the kernel table slot number.

              RefCount: the number of users of the socket.

              Protocol: currently always 0.

              Flags:    the  internal  kernel  flags holding the status of the
                        socket.

              Type:     the socket type.  For  SOCK_STREAM  sockets,  this  is
                        0001;  for  SOCK_DGRAM  sockets,  it  is 0002; and for
                        SOCK_SEQPACKET sockets, it is 0005.

              St:       the internal state of the socket.

              Path:     the bound path (if any) of the socket.  Sockets in the
                        abstract  namespace  are included in the list, and are
                        shown with a Path that commences  with  the  character
                        '@'.

       /proc/net/netfilter/nfnetlink_queue
              This file contains information about netfilter user-space queue-
              ing, if used.  Each line represents a queue.  Queues  that  have
              not been subscribed to by user space are not shown.

                     1   4207     0  2 65535     0     0        0  1
                    (1)   (2)    (3)(4)  (5)    (6)   (7)      (8)

              The fields in each line are:

              (1)  The ID of the queue.  This matches what is specified in the
                   --queue-num or --queue-balance options to  the  iptables(8)
                   NFQUEUE target.  See iptables-extensions(8) for more infor-
                   mation.

              (2)  The netlink port ID subscribed to the queue.

              (3)  The number of packets currently queued and  waiting  to  be
                   processed by the application.

              (4)  The copy mode of the queue.  It is either 1 (metadata only)
                   or 2 (also copy payload data to user space).

              (5)  Copy range; that is,  how  many  bytes  of  packet  payload
                   should be copied to user space at most.

              (6)  queue dropped.  Number of packets that had to be dropped by
                   the kernel because too many packets are already waiting for
                   user space to send back the mandatory accept/drop verdicts.

              (7)  queue  user  dropped.   Number of packets that were dropped
                   within the netlink subsystem.  Such  drops  usually  happen
                   when the corresponding socket buffer is full; that is, user
                   space is not able to read messages fast enough.

              (8)  sequence number.  Every queued packet is associated with  a
                   (32-bit)  monotonically-increasing  sequence  number.  This
                   shows the ID of the most recent packet queued.

              The last number exists only for compatibility reasons and is al-
              ways 1.

       /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.  See slabinfo(5) for details.

       /proc/stat
              kernel/system statistics.  Varies with architecture.  Common en-
              tries include:

              cpu 10132153 290696 3084719 46828483 16683 0 25195 0 175628 0
              cpu0 1393280 32966 572056 13343292 6130 0 17875 0 23933 0
                     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 ("cpu" line) or the  specific  CPU  ("cpuN"  line)
                     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.  This  value
                            is not reliable, for the following reasons:

                            1. The  CPU  will  not  wait  for I/O to complete;
                               iowait is the time that a task is  waiting  for
                               I/O  to  complete.   When  a CPU goes into idle
                               state for outstanding task  I/O,  another  task
                               will be scheduled on this CPU.

                            2. On  a  multi-core CPU, the task waiting for I/O
                               to complete is not running on any CPU,  so  the
                               iowait of each CPU is difficult to calculate.

                            3. The value in this field may decrease in certain
                               conditions.

                     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 op-
                            erating  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  in-
                     cluding unnumbered architecture specific interrupts; each
                     subsequent column is the total for that  particular  num-
                     bered  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 on-
                     ward.)

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

              softirq 229245889 94 60001584 13619 5175704 2471304 28  51212741
              59130143 0 51240672
                     This  line shows the number of softirq for all CPUs.  The
                     first column is the total of all softirqs and each subse-
                     quent column is the total for particular softirq.  (Linux
                     2.6.31 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.

              String values may be terminated by either '\0' or '\n'.

              Integer  and  long values may be written either in decimal or in
              hexadecimal notation (e.g. 0x3FFF).  When writing multiple inte-
              ger or long values, these may be separated by any of the follow-
              ing whitespace characters: ' ', '\t', or '\n'.  Using other sep-
              arators leads to the error EINVAL.

       /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   source   in   the   file   Documentation/admin-
              guide/binfmt-misc.rst  (or  in  Documentation/binfmt_misc.txt on
              older kernels).

       /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  re-
              quested by system) and two dummy values.

              * nr_dentry  is  the  number  of  allocated dentries (dcache en-
                tries).  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.  System calls that fail when encounter-
              ing  this  limit  fail  with  the error ENFILE.  (See also setr-
              limit(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 increasing this value:

                  echo 100000 > /proc/sys/fs/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 al-
              located 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  in-
              dicates  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_in-
              stances,  and  max_user_watches,  that  can be used to limit the
              amount of kernel memory consumed by the inotify interface.   For
              further details, see inotify(7).

       /proc/sys/fs/lease-break-time
              This file specifies the grace period that the kernel grants to a
              process holding a file lease (fcntl(2)) after it has sent a 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  (fc-
              ntl(2)) on a system-wide basis.  If this file contains the value
              0, leases are disabled.  A nonzero value enables leases.

       /proc/sys/fs/mount-max (since Linux 4.9)
              The value in this file specifies the maximum  number  of  mounts
              that  may exist in a mount namespace.  The default value in this
              file is 100,000.

       /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/nr_open (since Linux 2.6.25)
              This  file  imposes  ceiling  on  the   value   to   which   the
              RLIMIT_NOFILE  resource  limit can be raised (see getrlimit(2)).
              This ceiling is enforced for both  unprivileged  and  privileged
              process.   The  default  value in this file is 1048576.  (Before
              Linux 2.6.25, the ceiling for RLIMIT_NOFILE  was  hard-coded  to
              the same value.)

       /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  en-
              abled,  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)
              See pipe(7).

       /proc/sys/fs/pipe-user-pages-hard (since Linux 4.5)
              See pipe(7).

       /proc/sys/fs/pipe-user-pages-soft (since Linux 4.5)
              See pipe(7).

       /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 calling process has the CAP_FOWNER capability in its user
                 namespace and the file UID has a mapping in the namespace.

              *  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  mode  bit
                     enabled;

                  o  the  target  file does not have both its set-group-ID and
                     group-executable mode 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  be-
              ing 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 is assigned to a process's "dumpable"
              flag in the circumstances described in prctl(2).  In effect, the
              value  in  this file determines whether core dump files are pro-
              duced for set-user-ID or otherwise  protected/tainted  binaries.
              The  "dumpable" setting also affects the ownership of files in a
              process's /proc/[pid] directory, as described above.

              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.  (Reasons why a
                     process might nevertheless not dump core are described in
                     core(5).)   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:
                     this mode is  insecure  because  it  allows  unprivileged
                     users  to  examine the memory contents of privileged pro-
                     cesses.

              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  ap-
                     propriate  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.

              For details of the effect of a process's "dumpable"  setting  on
              ptrace access mode checking, see ptrace(2).

       /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  pa-
              rameters, 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/auto_msgmni (Linux 2.6.27 to 3.18)
              From Linux 2.6.27 to 3.18, this file was used to control  recom-
              puting of the value in /proc/sys/kernel/msgmni upon the addition
              or removal of memory or  upon  IPC  namespace  creation/removal.
              Echoing  "1" into this file enabled msgmni automatic recomputing
              (and triggered a recomputation of msgmni based  on  the  current
              amount of available memory and number of IPC namespaces).  Echo-
              ing "0" disabled automatic recomputing.  (Automatic  recomputing
              was  also  disabled  if  a  value  was  explicitly  assigned  to
              /proc/sys/kernel/msgmni.)  The default value in auto_msgmni  was
              1.

              Since  Linux  3.19,  the content of this file has no effect (be-
              cause msgmni defaults to near the maximum value  possible),  and
              reads from this file always return the value "0".

       /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 ex-
              ecve(2).  Starting with Linux 2.6.25, the system-wide capability
              bounding  set  disappeared,  and  was  replaced  by a per-thread
              bounding set; see capabilities(7).

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

       /proc/sys/kernel/core_pipe_limit
              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(1) 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  in-
              tercepted  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 (before Linux 2.4.9.2)
              (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/keys/*
              This directory contains various files that define parameters and
              limits for the key-management facility.   These  files  are  de-
              scribed in keyrings(7).

       /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.  En-
              abled 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.  See also /proc/sys/kernel/auto_msgmni.

       /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/ns_last_pid (since Linux 3.3)
              See pid_namespaces(7).

       /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 non-
              zero, then the machine will be rebooted.

       /proc/sys/kernel/pid_max (since Linux 2.5.34)
              This file specifies the value at which PIDs wrap  around  (i.e.,
              the  value  in  this  file is one greater than the maximum PID).
              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/randomize_va_space (since Linux 2.6.12)
              Select the address space layout randomization (ASLR) policy  for
              the  system  (on architectures that support ASLR).  Three values
              are supported for this file:

              0  Turn ASLR off.  This is the default  for  architectures  that
                 don't  support  ASLR,  and when the kernel is booted with the
                 norandmaps parameter.

              1  Make the addresses of mmap(2) allocations, the stack, and the
                 VDSO  page  randomized.   Among other things, this means that
                 shared libraries will be loaded at randomized addresses.  The
                 text  segment of PIE-linked binaries will also be loaded at a
                 randomized address.  This value is the default if the  kernel
                 was configured with CONFIG_COMPAT_BRK.

              2  (Since  Linux  2.6.25) Also support heap randomization.  This
                 value is the default if the kernel was  not  configured  with
                 CONFIG_COMPAT_BRK.

       /proc/sys/kernel/real-root-dev
              This file is documented in the Linux kernel source file Documen-
              tation/admin-guide/initrd.rst (or  Documentation/initrd.txt  be-
              fore Linux 4.10).

       /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  re-
              booting?

       /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 of POSIX real-time signals currently queued.

       /proc/[pid]/sched_autogroup_enabled (since Linux 2.6.38)
              See sched(7).

       /proc/sys/kernel/sched_child_runs_first (since Linux 2.6.23)
              If this file contains the value zero, then, after a fork(2), the
              parent  is  first  scheduled on the CPU.  If the file contains a
              nonzero value, then the child is scheduled  first  on  the  CPU.
              (Of course, on a multiprocessor system, the parent and the child
              might both immediately be scheduled on a CPU.)

       /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/seccomp (since Linux 4.14)
              This directory provides additional seccomp information and  con-
              figuration.  See seccomp(2) for further details.

       /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 de-
              stroy segments that were created, but never attached, upon  ter-
              mination 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.  Set this file to 1 only 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/sysctl_writes_strict (since Linux 3.16)
              The  value  in  this file determines how the file offset affects
              the behavior of updating entries in files under /proc/sys.   The
              file has three possible values:

              -1  This  provides  legacy  handling,  with  no printk warnings.
                  Each write(2) must fully contain the value  to  be  written,
                  and  multiple  writes on the same file descriptor will over-
                  write the entire value, regardless of the file position.

              0   (default) This provides the same behavior  as  for  -1,  but
                  printk  warnings  are  written  for  processes  that perform
                  writes when the file offset is not 0.

              1   Respect the file offset when writing strings into  /proc/sys
                  files.   Multiple  writes  will  append to the value buffer.
                  Anything written beyond the maximum length of the value buf-
                  fer  will  be  ignored.  Writes to numeric /proc/sys entries
                  must always be at file offset 0 and the value must be  fully
                  contained in the buffer provided to write(2).

       /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/admin-guide/sysrq.rst (or Docu-
              mentation/sysrq.txt before Linux 4.10).

       /proc/sys/kernel/version
              This file contains a string such as:

                  #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 following 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.

              Since Linux 4.1, the value that can be written to threads-max is
              bounded.  The minimum value that can be written is 20.  The max-
              imum value that can be written is  given  by  the  constant  FU-
              TEX_TID_MASK  (0x3fffffff).  If a value outside of this range is
              written to threads-max, the error EINVAL occurs.

              The value written is checked against the  available  RAM  pages.
              If the thread structures would occupy too much (more than 1/8th)
              of the available RAM pages, threads-max is reduced accordingly.

       /proc/sys/kernel/yama/ptrace_scope (since Linux 3.5)
              See ptrace(2).

       /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/bpf_jit_enable
              See bpf(2).

       /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/user (since Linux 4.9)
              See namespaces(7).

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

       /proc/sys/vm/admin_reserve_kbytes (since Linux 3.10)
              This file defines the amount of free memory (in KiB) on the sys-
              tem that should  be  reserved  for  users  with  the  capability
              CAP_SYS_ADMIN.

              The  default  value  in  this file is the minimum of [3% of free
              pages, 8MiB] expressed as KiB.  The default is intended to  pro-
              vide  enough  for the superuser to log in and kill a process, if
              necessary, under the default overcommit 'guess' mode (i.e., 0 in
              /proc/sys/vm/overcommit_memory).

              Systems   running   in  "overcommit  never"  mode  (i.e.,  2  in
              /proc/sys/vm/overcommit_memory) should  increase  the  value  in
              this  file  to  account  for the full virtual memory size of the
              programs used to recover (e.g.,  login(1)  ssh(1),  and  top(1))
              Otherwise,  the  superuser  may not be able to log in to recover
              the system.  For example, on x86-64 a suitable value  is  131072
              (128MiB reserved).

              Changing  the value in this file takes effect whenever an appli-
              cation requests memory.

       /proc/sys/vm/compact_memory (since Linux 2.6.35)
              When 1 is written to this file, all  zones  are  compacted  such
              that  free memory is available in contiguous blocks where possi-
              ble.  The effect  of  this  action  can  be  seen  by  examining
              /proc/buddyinfo.

              Present  only  if  the  kernel  was  configured with CONFIG_COM-
              PACTION.

       /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  de-
              grade 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  that  this  is not supported for a few types of pages,
                  such as kernel internally allocated data or the swap  cache,
                  but works for the majority of user pages.

              0:  Unmap  the  corrupted  page  from  all  processes and kill a
                  process only if it tries to access the page.

              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  ad-
              vanced  machine check handling and depends on the hardware capa-
              bilities.

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

              Present  only  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.

              Present only 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  in-
              cludes   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 de-
              termine 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 en-
              tire 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".

              In  mode  1,  the kernel pretends there is always enough memory,
              until memory actually runs out.  One use case for this  mode  is
              scientific  computing  applications that employ large sparse ar-
              rays.  In Linux kernel versions before 2.6.0, 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

              See also the description  of  /proc/sys/vm/admiin_reserve_kbytes
              and /proc/sys/vm/user_reserve_kbytes.

       /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/sys/vm/user_reserve_kbytes (since Linux 3.10)
              Specifies  an amount of memory (in KiB) to reserve for user pro-
              cesses, This is intended to prevent a user from starting a  sin-
              gle  memory hogging process, such that they cannot recover (kill
              the hog).  The value in  this  file  has  an  effect  only  when
              /proc/sys/vm/overcommit_memory  is  set to 2 ("overcommit never"
              mode).  In this case, the system reserves an  amount  of  memory
              that  is  the  minimum  of [3% of current process size, user_re-
              serve_kbytes].

              The default value in this file is the minimum  of  [3%  of  free
              pages, 128MiB] expressed as KiB.

              If  the  value  in this file is set to zero, then a user will be
              allowed to allocate all free memory with a single process (minus
              the  amount reserved by /proc/sys/vm/admin_reserve_kbytes).  Any
              subsequent attempts to execute a command will result  in  "fork:
              Cannot allocate memory".

              Changing  the value in this file takes effect whenever an appli-
              cation requests memory.

       /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/admin-guide/sysrq.rst (or Documentation/sysrq.txt be-
              fore Linux 4.10).

       /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 un-
              derstanding.  svipc(7) provides further background on the infor-
              mation shown by these files.

       /proc/thread-self (since Linux 3.17)
              This directory refers to the thread accessing the /proc filesys-
              tem,  and  is  identical  to the /proc/self/task/[tid] directory
              named by the process thread ID ([tid]) of the same thread.

       /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 pa-
              rameters in a human-readable form.

       /proc/timer_stats (from  Linux 2.6.21 until Linux 4.10)
              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 run-time overhead and a relatively small data-
              structure overhead.  Even if collection is enabled at run  time,
              overhead  is  low:  all  the  locking  is  per-CPU and lookup is
              hashed.

              The /proc/timer_stats file is used both to control sampling  fa-
              cility 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.

              During the Linux 4.11 development cycle, this file  was  removed
              because  of  security concerns, as it exposes information across
              namespaces.  Furthermore, it is possible to obtain the same  in-
              formation via in-kernel tracing facilities such as ftrace.

       /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 2.6.0)
              This file displays various virtual memory statistics.  Each line
              of  this  file  contains  a single name-value pair, delimited by
              white space.  Some lines are present only if the kernel was con-
              figured  with suitable options.  (In some cases, the options re-
              quired for particular files have changed across kernel versions,
              so they are not listed here.  Details can be found by consulting
              the kernel source code.)  The following fields may be present:

              nr_free_pages (since Linux 2.6.31)

              nr_alloc_batch (since Linux 3.12)

              nr_inactive_anon (since Linux 2.6.28)

              nr_active_anon (since Linux 2.6.28)

              nr_inactive_file (since Linux 2.6.28)

              nr_active_file (since Linux 2.6.28)

              nr_unevictable (since Linux 2.6.28)

              nr_mlock (since Linux 2.6.28)

              nr_anon_pages (since Linux 2.6.18)

              nr_mapped (since Linux 2.6.0)

              nr_file_pages (since Linux 2.6.18)

              nr_dirty (since Linux 2.6.0)

              nr_writeback (since Linux 2.6.0)

              nr_slab_reclaimable (since Linux 2.6.19)

              nr_slab_unreclaimable (since Linux 2.6.19)

              nr_page_table_pages (since Linux 2.6.0)

              nr_kernel_stack (since Linux 2.6.32)
                     Amount of memory allocated to kernel stacks.

              nr_unstable (since Linux 2.6.0)

              nr_bounce (since Linux 2.6.12)

              nr_vmscan_write (since Linux 2.6.19)

              nr_vmscan_immediate_reclaim (since Linux 3.2)

              nr_writeback_temp (since Linux 2.6.26)

              nr_isolated_anon (since Linux 2.6.32)

              nr_isolated_file (since Linux 2.6.32)

              nr_shmem (since Linux 2.6.32)
                     Pages used by shmem and tmpfs(5).

              nr_dirtied (since Linux 2.6.37)

              nr_written (since Linux 2.6.37)

              nr_pages_scanned (since Linux 3.17)

              numa_hit (since Linux 2.6.18)

              numa_miss (since Linux 2.6.18)

              numa_foreign (since Linux 2.6.18)

              numa_interleave (since Linux 2.6.18)

              numa_local (since Linux 2.6.18)

              numa_other (since Linux 2.6.18)

              workingset_refault (since Linux 3.15)

              workingset_activate (since Linux 3.15)

              workingset_nodereclaim (since Linux 3.15)

              nr_anon_transparent_hugepages (since Linux 2.6.38)

              nr_free_cma (since Linux 3.7)
                     Number of free CMA (Contiguous Memory Allocator) pages.

              nr_dirty_threshold (since Linux 2.6.37)

              nr_dirty_background_threshold (since Linux 2.6.37)

              pgpgin (since Linux 2.6.0)

              pgpgout (since Linux 2.6.0)

              pswpin (since Linux 2.6.0)

              pswpout (since Linux 2.6.0)

              pgalloc_dma (since Linux 2.6.5)

              pgalloc_dma32 (since Linux 2.6.16)

              pgalloc_normal (since Linux 2.6.5)

              pgalloc_high (since Linux 2.6.5)

              pgalloc_movable (since Linux 2.6.23)

              pgfree (since Linux 2.6.0)

              pgactivate (since Linux 2.6.0)

              pgdeactivate (since Linux 2.6.0)

              pgfault (since Linux 2.6.0)

              pgmajfault (since Linux 2.6.0)

              pgrefill_dma (since Linux 2.6.5)

              pgrefill_dma32 (since Linux 2.6.16)

              pgrefill_normal (since Linux 2.6.5)

              pgrefill_high (since Linux 2.6.5)

              pgrefill_movable (since Linux 2.6.23)

              pgsteal_kswapd_dma (since Linux 3.4)

              pgsteal_kswapd_dma32 (since Linux 3.4)

              pgsteal_kswapd_normal (since Linux 3.4)

              pgsteal_kswapd_high (since Linux 3.4)

              pgsteal_kswapd_movable (since Linux 3.4)

              pgsteal_direct_dma

              pgsteal_direct_dma32 (since Linux 3.4)

              pgsteal_direct_normal (since Linux 3.4)

              pgsteal_direct_high (since Linux 3.4)

              pgsteal_direct_movable (since Linux 2.6.23)

              pgscan_kswapd_dma

              pgscan_kswapd_dma32 (since Linux 2.6.16)

              pgscan_kswapd_normal (since Linux 2.6.5)

              pgscan_kswapd_high

              pgscan_kswapd_movable (since Linux 2.6.23)

              pgscan_direct_dma

              pgscan_direct_dma32 (since Linux 2.6.16)

              pgscan_direct_normal

              pgscan_direct_high

              pgscan_direct_movable (since Linux 2.6.23)

              pgscan_direct_throttle (since Linux 3.6)

              zone_reclaim_failed (since linux 2.6.31)

              pginodesteal (since linux 2.6.0)

              slabs_scanned (since linux 2.6.5)

              kswapd_inodesteal (since linux 2.6.0)

              kswapd_low_wmark_hit_quickly (since 2.6.33)

              kswapd_high_wmark_hit_quickly (since 2.6.33)

              pageoutrun (since Linux 2.6.0)

              allocstall (since Linux 2.6.0)

              pgrotated (since Linux 2.6.0)

              drop_pagecache (since Linux 3.15)

              drop_slab (since Linux 3.15)

              numa_pte_updates (since Linux 3.8)

              numa_huge_pte_updates (since Linux 3.13)

              numa_hint_faults (since Linux 3.8)

              numa_hint_faults_local (since Linux 3.8)

              numa_pages_migrated (since Linux 3.8)

              pgmigrate_success (since Linux 3.8)

              pgmigrate_fail (since Linux 3.8)

              compact_migrate_scanned (since Linux 3.8)

              compact_free_scanned (since Linux 3.8)

              compact_isolated (since Linux 3.8)

              compact_stall (since Linux 2.6.35)
                     See  the  kernel   source   file   Documentation/vm/tran-
                     shuge.txt.

              compact_fail (since Linux 2.6.35)
                     See   the   kernel   source  file  Documentation/vm/tran-
                     shuge.txt.

              compact_success (since Linux 2.6.35)
                     See  the  kernel   source   file   Documentation/vm/tran-
                     shuge.txt.

              htlb_buddy_alloc_success (since Linux 2.6.26)

              htlb_buddy_alloc_fail (since Linux 2.6.26)

              unevictable_pgs_culled (since Linux 2.6.28)

              unevictable_pgs_scanned (since Linux 2.6.28)

              unevictable_pgs_rescued (since Linux 2.6.28)

              unevictable_pgs_mlocked (since Linux 2.6.28)

              unevictable_pgs_munlocked (since Linux 2.6.28)

              unevictable_pgs_cleared (since Linux 2.6.28)

              unevictable_pgs_stranded (since Linux 2.6.28)

              thp_fault_alloc (since Linux 2.6.39)
                     See   the   kernel   source  file  Documentation/vm/tran-
                     shuge.txt.

              thp_fault_fallback (since Linux 2.6.39)
                     See  the  kernel   source   file   Documentation/vm/tran-
                     shuge.txt.

              thp_collapse_alloc (since Linux 2.6.39)
                     See   the   kernel   source  file  Documentation/vm/tran-
                     shuge.txt.

              thp_collapse_alloc_failed (since Linux 2.6.39)
                     See  the  kernel   source   file   Documentation/vm/tran-
                     shuge.txt.

              thp_split (since Linux 2.6.39)
                     See   the   kernel   source  file  Documentation/vm/tran-
                     shuge.txt.

              thp_zero_page_alloc (since Linux 3.8)
                     See  the  kernel   source   file   Documentation/vm/tran-
                     shuge.txt.

              thp_zero_page_alloc_failed (since Linux 3.8)
                     See   the   kernel   source  file  Documentation/vm/tran-
                     shuge.txt.

              balloon_inflate (since Linux 3.18)

              balloon_deflate (since Linux 3.18)

              balloon_migrate (since Linux 3.18)

              nr_tlb_remote_flush (since Linux 3.12)

              nr_tlb_remote_flush_received (since Linux 3.12)

              nr_tlb_local_flush_all (since Linux 3.12)

              nr_tlb_local_flush_one (since Linux 3.12)

              vmacache_find_calls (since Linux 3.16)

              vmacache_find_hits (since Linux 3.16)

              vmacache_full_flushes (since Linux 3.19)

       /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), init(1), ps(1), tr(1), uptime(1),
       chroot(2),  mmap(2),  readlink(2),  syslog(2),  slabinfo(5),  sysfs(5),
       hier(7),   namespaces(7),   time(7),  arp(8),  hdparm(8),  ifconfig(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 4.16 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
       https://www.kernel.org/doc/man-pages/.

Linux                             2017-09-15                           PROC(5)

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