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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.  Typically, 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 following values:

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

              1   Users  may  not  access  files  and  subdirectories  inside   any   /proc/[pid]
                  directories  but  their  own  (the  /proc/[pid]  directories  themselves remain
                  visible).  Sensitive files such as /proc/[pid]/cmdline  and  /proc/[pid]/status
                  are  now  protected  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 information about running
                  processes (e.g., discovering whether  some  daemon  is  running  with  elevated
                  privileges,  whether  another  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.

   Overview
       Underneath /proc, there are the following general groups of files and subdirectories:

       /proc/[pid] subdirectories
              Each  one  of  these  subdirectories  contains  files  and  subdirectories exposing
              information about the process with the corresponding process ID.

              Underneath each of  the  /proc/[pid]  directories,  a  task  subdirectory  contains
              subdirectories  of  the  form  task/[tid],  which contain corresponding information
              about each of the threads in the process, where tid is the kernel thread ID of  the
              thread.

              The  /proc/[pid]  subdirectories  are  visible  when  iterating  through /proc with
              getdents(2) (and thus are visible when one uses  ls(1)  to  view  the  contents  of
              /proc).

       /proc/[tid] subdirectories
              Each  one  of  these  subdirectories  contains  files  and  subdirectories exposing
              information about the thread with the corresponding thread  ID.   The  contents  of
              these   directories  are  the  same  as  the  corresponding  /proc/[pid]/task/[tid]
              directories.

              The /proc/[tid] subdirectories are not visible when iterating  through  /proc  with
              getdents(2)  (and  thus are not visible when one uses ls(1) to view the contents of
              /proc).

       /proc/self
              When a process accesses this magic symbolic link, it resolves to the process's  own
              /proc/[pid] directory.

       /proc/thread-self
              When  a  thread accesses this magic symbolic link, it resolves to the process's own
              /proc/self/task/[tid] directory.

       /proc/[a-z]*
              Various other files and subdirectories under /proc expose system-wide information.

       All of the above are described in more detail below.

   Files and directories
       The following list provides details of 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 directories described below.

              The  files  inside  each  /proc/[pid] directory are normally owned by the effective
              user and effective group ID of the process.  However, as a  security  measure,  the
              ownership is made root:root if the process's "dumpable" attribute is set to a value
              other than 1.

              Before Linux 4.11, root:root meant the "global" root user ID and  group  ID  (i.e.,
              UID  0  and GID 0 in the initial user namespace).  Since Linux 4.11, if the process
              is in a noninitial user namespace that has a valid mapping for user  (group)  ID  0
              inside  the  namespace,  then  the  user  (group)  ownership  of  the  files  under
              /proc/[pid] is instead made the same as the root user (group) ID of the  namespace.
              This  means  that  inside  a  container,  things work as expected for the container
              "root" user.

              The process's "dumpable" 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 effective UID and GID.  Note, however, that if the effective
              UID or GID is subsequently modified, then the "dumpable" attribute may be reset, as
              described in prctl(2).  Therefore, it may be  desirable  to  reset  the  "dumpable"
              attribute after making any desired changes to the process's effective UID or 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 directory 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 attributes 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 policy, although use of this operation is only suitable for
              applications that are trusted to maintain any desired separation  between  the  old
              and new security contexts.

              Prior to Linux 2.6.28, SELinux did not allow threads within a multithreaded 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 context has a subset of the permissions of the old
              security context.

              Other security modules may choose to support "set" operations 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  multiple  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 subsequently 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/security/keys.txt   on   Linux   between    3.0    and    4.13,    or
              Documentation/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  subsequently  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)
              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 using.  One first inspects the values in
              the "Referenced" fields for the VMAs shown in /proc/[pid]/smaps to get an  idea  of
              the  memory  footprint  of  the  process.   One  then  clears the PG_Referenced and
              ACCESSED/YOUNG bits and, after some measured time interval, once again inspects the
              values  in the "Referenced" fields to get an idea of the change in memory footprint
              of the process during  the  measured  interval.   If  one  is  interested  only  in
              inspecting the selected mapping types, then the value 2 or 3 can be used instead of
              1.

              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 CONFIG_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.

              If, after an execve(2), the process modifies its argv strings, those  changes  will
              show up here.  This is not the same thing as modifying the argv array.

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

              Think of this file as the command line that the process wants you to see.

       /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 (including the terminating null
              byte) 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.  The value in this file is used  for  the  %e  specifier  in
              /proc/sys/kernel/core_pattern; see core(5).

       /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; 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_FSCREDS 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 entries are separated by null
              bytes ('\0'), and there may be a null byte at the end.   Thus,  to  print  out  the
              environment of process 1, you would do:

                  $ cat /proc/1/environ | tr '\000' '\n'

              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 containing the actual
              pathname of the executed command.  This symbolic link can be dereferenced normally;
              attempting  to open it will open the executable.  You can even type /proc/[pid]/exe
              to run another copy of the same executable 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  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_FSCREDS 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 information 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 symbolic 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 (typically 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  argument, but don't send their output to standard output if no
              argument 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  designating  an  input  file  and  -o  is  the  flag
              designating an output file:

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

              and you have a working filter.

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

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

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

              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 descriptor.

              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 descriptors 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)   (expressed   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 hexadecimal).

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

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

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

              For  timerfd  file  descriptors  (see  timerfd(2)),  we  see (since Linux 3.17) the
              following fields:

                  pos:    0
                  flags:  02004002
                  mnt_id: 13
                  clockid: 0
                  ticks: 0
                  settime flags: 03
                  it_value: (7695568592, 640020877)
                  it_interval: (0, 0)

              clockid
                     This is the numeric value of the clock  ID  (corresponding  to  one  of  the
                     CLOCK_* constants defined via <time.h>) that is used to mark the progress of
                     the timer (in this example, 0 is CLOCK_REALTIME).

              ticks  This is the number of timer expirations that have occurred, (i.e., the value
                     that read(2) on it would return).

              settime flags
                     This  field  lists  the  flags  with  which  the timerfd was last armed (see
                     timerfd_settime(2)), in octal (in this example, both  TFD_TIMER_ABSTIME  and
                     TFD_TIMER_CANCEL_ON_SET are set).

              it_value
                     This  field  contains  the  amount of time until the timer will next expire,
                     expressed in seconds  and  nanoseconds.   This  is  always  expressed  as  a
                     relative  value,  regardless  of  whether  the  timer  was created using the
                     TFD_TIMER_ABSTIME flag.

              it_interval
                     This field contains the interval of the timer, in seconds  and  nanoseconds.
                     (The   it_value   and   it_interval   fields   contain   the   values   that
                     timerfd_gettime(2) on this file descriptor would return.)

       /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 1 MB to a file and
                     then  deletes  the  file,  it will in fact perform no writeout.  But it will
                     have been accounted as having caused 1 MB 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 measurement for each of
              the process's resource limits  (see  getrlimit(2)).   Up  to  and  including  Linux
              2.6.35,  this  file  is  protected  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 implemented in Linux means that such regions  also  appear  on
              this  directory.  Here is an example where the target file is the deleted /dev/zero
              one:

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

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

              Until    kernel    version    4.3,    this   directory   appeared   only   if   the
              CONFIG_CHECKPOINT_RESTORE kernel configuration option was enabled.

              Capabilities are required to read the  contents  of  the  symbolic  links  in  this
              directory:  before  Linux  5.9,  the  reading process requires CAP_SYS_ADMIN in the
              initial user namespace; since Linux 5.9,  the  reading  process  must  have  either
              CAP_SYS_ADMIN or CAP_CHECKPOINT_RESTORE in the user namespace where it resides.

       /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 offset 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>] (from Linux 3.4 to 4.4)
                     A  thread's  stack  (where the <tid> is a thread ID).  It corresponds to the
                     /proc/[pid]/task/[tid]/ path.  This field was removed in  Linux  4.5,  since
                     providing  this  information  for a process with large numbers of threads is
                     expensive.

              [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.

              pathname is shown unescaped except for newline characters, which are replaced  with
              an octal escape sequence.  As a result, it is not possible to determine whether the
              original pathname contained a newline  character  or  the  literal  \012  character
              sequence.

              If  the  mapping  is  file-backed  and  the  file  has  been  deleted, the string "
              (deleted)" is appended to the pathname.  Note that this is ambiguous too.

              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  supplies  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., nonextensibility, 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 below:

              (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 a new mount is stacked on top of a previous  existing  mount  (so  that  it
                   hides  the  existing mount) at pathname P, then the parent of the new mount is
                   the previous mount at that location.  Thus, when looking  at  all  the  mounts
                   stacked  at  a  particular location, the top-most mount is the one that is not
                   the parent of any other mount at the same location.  (Note, however, that this
                   top-most mount will be accessible only if the longest path subprefix of P that
                   is a mount point is not itself hidden by a stacked mount.)

                   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 filesystem (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 (see mount(2)).

              (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 (see mount(2)).

              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 unrecognized optional fields.

              For       more       information       on       mount       propagation        see:
              Documentation/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 opening the file for
              reading, a change in this  file  (i.e.,  a  filesystem  mount  or  unmount)  causes
              select(2)  to  mark  the  file  descriptor  as having an exceptional condition, and
              poll(2) and epoll_wait(2) mark the file  as  having  a  priority  event  (POLLPRI).
              (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 information) 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 [stats]
                  (       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.   Currently  (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 information, see namespaces(7).

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

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

              The  default  value for this file is 0; a new process inherits its parent's oom_adj
              setting.  A process must be privileged (CAP_SYS_RESOURCE) to update this file.

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

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

              * whether the process 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  exhausted,  the
              allowed  memory  represents  the  set of mempolicy nodes.  If it is due to a memory
              limit (or swap limit) being reached, the allowed memory is that  configured  limit.
              Finally,  if it is due to the entire system being out of memory, the allowed memory
              represents all allocatable resources.

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

              Consequently, it is very simple for user space to define the amount  of  memory  to
              consider  for  each  task.  Setting 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 allowed memory from being considered as scoring against the task.

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

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

              The   choom(1)   program  provides  a  command-line  interface  for  adjusting  the
              oom_score_adj value of a running process or a newly executed command.

       /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 follows:

              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
                     Documentation/admin-guide/mm/soft-dirty.rst).

              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 CONFIG_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_FSCREDS 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.  (Further 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 displayed 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.   "Anonymous"  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 64 kB as a base page size may still use 4 kB pages  for  the
              MMU on older processors.  To distinguish the two attributes, 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)) associated with the virtual memory area.  This
              entry   is    present    only    if    the    kernel    was    built    with    the
              CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS configuration option (since Linux 4.6).

              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
                  sf  - perform synchronous page faults (since Linux 4.15)
                  nl  - non-linear mapping (removed in Linux 4.0)
                  ar  - architecture specific flag
                  wf  - wipe on fork (since Linux 4.14)
                  dd  - do not include area into core dump
                  sd  - soft-dirty flag (since Linux 3.13)
                  mm  - mixed map area
                  hg  - huge page advise flag
                  nh  - no-huge page advise flag
                  mg  - mergeable advise flag
                  um  - userfaultfd missing pages tracking (since Linux 4.3)
                  uw  - userfaultfd wprotect pages tracking (since Linux 4.3)

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

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

              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  specifiers,  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.   Strings  longer  than
                     TASK_COMM_LEN  (16)  characters  (including  the  terminating null byte) are
                     silently truncated.  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 controlling terminal of the
                     process.

              (9) flags  %u
                     The kernel flags word of the  process.   For  bit  meanings,  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  below),  so   that
                     applications  that  are  not  aware of the guest time field do not lose that
                     time from their calculations.

              (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
                     (setpriority(2)) as represented in  the  kernel.   The  kernel  stores  nice
                     values  as  numbers  in the range 0 (high) to 39 (low), corresponding to the
                     user-visible nice range of -20 to 19.

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

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

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

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

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

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

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

              (24) rss  %ld
                     Resident Set Size: number of pages the process has in real memory.  This  is
                     just the pages which count toward text, data, or stack space.  This does not
                     include pages which have not been demand-loaded in,  or  which  are  swapped
                     out.  This value is inaccurate; see /proc/[pid]/statm below.

              (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  information  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  information  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  information  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  information  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 policy, 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  virtual  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  uninitialized  (BSS)  data  are
                     placed.

              (46) end_data  %lu  (since Linux 3.3)  [PT]
                     Address  below  which  program  initialized and uninitialized (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 waitpid(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
                             (inaccurate; same as VmRSS in /proc/[pid]/status)
                  shared     (3) number of resident shared pages
                             (i.e., backed by a file)
                             (inaccurate; 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)

              Some of these values  are  inaccurate  because  of  a  kernel-internal  scalability
              optimization.    If   accurate   values  are  required,  use  /proc/[pid]/smaps  or
              /proc/[pid]/smaps_rollup instead, which  are  much  slower  but  provide  accurate,
              detailed information.

       /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
                  CoreDumping:   0                       # 4.15
                  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
                  Speculation_Store_Bypass:       vulnerable
                  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.   Strings  longer  than  TASK_COMM_LEN  (16)
                     characters (including the terminating null byte) are silently truncated.

              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 namespaces of which [pid]  is
                     a  member.   The  leftmost  entry  shows  the  value with respect to the PID
                     namespace of the process that mounted this procfs (or the root namespace  if
                     mounted  by  the kernel), 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 NStgid.  (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(2)).

              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").  This value is inaccurate; see
                     /proc/[pid]/statm above.

              VmRSS  Resident set size.  Note that the value here is the sum of RssAnon, RssFile,
                     and RssShmem.  This value is inaccurate; see /proc/[pid]/statm above.

              RssAnon
                     Size  of  resident  anonymous  memory.   (since  Linux  4.5).  This value is
                     inaccurate; see /proc/[pid]/statm above.

              RssFile
                     Size  of  resident  file  mappings.   (since  Linux  4.5).   This  value  is
                     inaccurate; see /proc/[pid]/statm above.

              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.   This  value  is  inaccurate;  see
                     /proc/[pid]/statm above.

              VmLib  Shared library code size.

              VmPTE  Page table entries size (since Linux 2.6.10).

              VmPMD  Size  of  second-level  page  tables  (added  in Linux 4.0; removed in Linux
                     4.15).

              VmSwap Swapped-out virtual memory size by anonymous private pages; shmem swap usage
                     is  not  included  (since  Linux  2.6.34).   This  value  is inaccurate; see
                     /proc/[pid]/statm above.

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

              CoreDumping
                     Contains the value 1 if the process is currently dumping core, and 0  if  it
                     is  not  (since  Linux  4.15).  This information can be used by a monitoring
                     process to avoid killing a process that is  currently  dumping  core,  which
                     could result in a corrupted core dump file.

              Threads
                     Number of threads in process containing this thread.

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

              SigPnd, ShdPnd
                     Mask  (expressed  in  hexadecimal)  of  signals  pending  for thread and for
                     process as a whole (see pthreads(7) and signal(7)).

              SigBlk, SigIgn, SigCgt
                     Masks (expressed in hexadecimal) indicating signals being blocked,  ignored,
                     and caught (see signal(7)).

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

              CapBnd Capability bounding set, expressed in hexadecimal (since Linux  2.6.26,  see
                     capabilities(7)).

              CapAmb Ambient  capability  set,  expressed  in  hexadecimal  (since Linux 4.3, see
                     capabilities(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    SECCOMP_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.

              Speculation_Store_Bypass
                     Speculation flaw mitigation state (since Linux 4.17, see prctl(2)).

              Cpus_allowed
                     Hexadecimal  mask of CPUs on which this process may run (since Linux 2.6.24,
                     see cpuset(7)).

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

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

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

              voluntary_ctxt_switches, nonvoluntary_ctxt_switches
                     Number of voluntary and involuntary context switches (since Linux 2.6.23).

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

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

              This    file    is    present    only   if   the   kernel   was   configured   with
              CONFIG_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)
              This  is a directory that contains one subdirectory for each thread in the process.
              The name of each subdirectory is the numerical thread ID ([tid]) of the thread (see
              gettid(2)).

              Within  each  of  these subdirectories, there is a set of files with the same names
              and contents as under the /proc/[pid] directories.  For attributes that are  shared
              by  all  threads,  the  contents  for  each  of  the  files  under  the  task/[tid]
              subdirectories will be the  same  as  in  the  corresponding  file  in  the  parent
              /proc/[pid]  directory (e.g., in a multithreaded process, all of the task/[tid]/cwd
              files will have the same value as the /proc/[pid]/cwd file in the parent directory,
              since  all  of the threads in a process share a working directory).  For attributes
              that are distinct for each thread, the corresponding  files  under  task/[tid]  may
              have  different values (e.g., various fields in each of the task/[tid]/status files
              may be different for each thread), or they might not exist in /proc/[pid] at all.

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

       /proc/[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 probably 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 example:

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

              The lines shown for each timer have the following meanings:

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

              signal This is the signal number that this  timer  uses  to  deliver  notifications
                     followed  by  a slash, and then the sigev_value 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 notifications via a signal.

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

              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,  expressed  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/[tid]
              There  is a numerical subdirectory for each running thread that  is  not  a  thread
              group  leader  (i.e.,  a thread whose thread ID is not the same as its process ID);
              the subdirectory is named by the thread  ID.   Each  one  of  these  subdirectories
              contains  files  and  subdirectories exposing information about the thread with the
              thread ID tid.  The contents of these directories are the same as the corresponding
              /proc/[pid]/task/[tid] directories.

              The  /proc/[tid]  subdirectories  are not visible when iterating through /proc with
              getdents(2) (and thus are not visible when one uses ls(1) to view the  contents  of
              /proc).   However,  the pathnames of these directories are visible to (i.e., usable
              as arguments in) system calls that operate on pathnames.

       /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 memory fragmentation
              issues.  Each line starts with the identification of the node and the name  of  the
              zone  which  together identify 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 kilobytes, then the first zone called
              DMA  (on  x86 the first 16 megabyte of memory) has 1 chunk of 4 kilobytes (order 0)
              available and has 3 chunks of 4 megabytes (order 10) available.

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

              Further information about the zones can be found in /proc/zoneinfo.

       /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 configuring 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  Documentation/crypto/  (or  Documentation/DocBook   before   4.10;   the
              documentation  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 bogomips; a system constant that is calculated  during  kernel
              initialization.   SMP machines have information for each CPU.  The lscpu(1) command
              gathers its information from this file.

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

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

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

       /proc/driver
              Empty subdirectory.

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

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

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

              Incidentally, this file may be used by mount(8) when no filesystem is specified and
              it  didn't  manage to determine the filesystem 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 information about (certain)
              mounted filesystems.

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

                  cache              buffer size in KB
                  capacity           number of sectors
                  driver             driver version
                  geometry           physical and logical geometry
                  identify           in hexadecimal
                  media              media type
                  model              manufacturer's model number
                  settings           drive settings
                  smart_thresholds   IDE disk management thresholds (in hex)
                  smart_values       IDE disk management values (in hex)

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

       /proc/interrupts
              This is used to record the number of interrupts per CPU per IO device.  Since Linux
              2.6.24,  for  the  i386  and  x86-64  architectures,  at  least, this also includes
              interrupts internal to the system (that is, not associated with a device as  such),
              such  as  NMI  (nonmaskable  interrupt),  LOC  (local timer interrupt), and for SMP
              systems, TLB (TLB flush  interrupt),  RES  (rescheduling  interrupt),  CAL  (remote
              function  call interrupt), and possibly others.  Very easy to read formatting, done
              in ASCII.

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

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

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

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

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

              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  CONFIG_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 discussion 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 kernel source file
              Documentation/admin-guide/mm/pagemap.rst.   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 CONFIG_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 separated
              by a slash (/).  The first of these is the  number  of  currently  runnable  kernel
              scheduling  entities (processes, threads).  The value after the slash is the number
              of kernel scheduling entities that currently exist on the system.  The fifth  field
              is the PID of the process that was most recently created on the system.

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

              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 fcntl(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 filtered  to  show  just
              the  locks for the processes in the PID namespace (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 memory (both physical  and  swap)  on
              the  system as well as the shared memory and buffers used by the kernel.  Each line
              of the file consists of a parameter name, followed by a colon,  the  value  of  the
              parameter,  and  an  option  unit  of  measurement  (e.g.,  "kB").   The list below
              describes the parameter names and the format specifier required to read  the  field
              value.   Except  as noted below, all of the fields have been present since at least
              Linux 2.6.0.  Some fields are displayed only if  the  kernel  was  configured  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 (20 MB or so).

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

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

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

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

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

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

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

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

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

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

              HighTotal %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)  Total  amount  of
                     highmem.   Highmem  is all memory above ~860 MB 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 everything  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.

              KReclaimable %lu (since Linux 4.20)
                     Kernel allocations that the kernel will  attempt  to  reclaim  under  memory
                     pressure.   Includes SReclaimable (below), and other direct allocations with
                     a shrinker.

              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 pressure.

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

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

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

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

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

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

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

              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
                     1 GB of memory (using malloc(3) or similar), but touches only 300 MB of that
                     memory  will  show  up  as  using  only  300 MB of memory even if it has the
                     address space allocated for the entire 1 GB.

                     This 1 GB is memory which has been "committed" to by the VM and can be  used
                     at  any  time by the allocating application.  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.  Since Linux 4.4, this field is no
                     longer calculated, and is hard coded as 0.  See /proc/vmallocinfo.

              VmallocChunk %lu
                     Largest contiguous block of vmalloc area which is free.   Since  Linux  4.4,
                     this   field  is  no  longer  calculated  and  is  hard  coded  as  0.   See
                     /proc/vmallocinfo.

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

              LazyFree %lu (since Linux 4.12)
                     Shows the amount of memory marked by madvise(2) MADV_FREE.

              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.  (CONFIG_CMA is required.)

              CmaFree %lu (since Linux 3.1)
                     Free CMA (Contiguous Memory Allocator) pages.  (CONFIG_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_overcommit_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 4 kB pages.  (x86.)

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

              DirectMap2M %lu (since Linux 2.6.27)
                     Number  of  bytes of RAM linearly mapped by kernel in 2 MB pages.  (x86 with
                     neither CONFIG_X86_64 nor CONFIG_X86_PAE enabled.)

              DirectMap1G %lu (since Linux 2.6.27)
                     (x86 with CONFIG_X86_64 and CONFIG_X86_DIRECT_GBPAGES enabled.)

       /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 filesystems currently mounted
              on  the  system.   With  the  introduction of per-process mount namespaces in Linux
              2.4.19 (see mount_namespaces(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  containing  information
              about the networking layer.  The files contain ASCII structures and are, therefore,
              readable with cat(1).  However, the standard netstat(8) suite provides much cleaner
              access to these files.

              With  the advent of network namespaces, various information relating to the network
              stack is  virtualized  (see  network_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 directories 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  kernel  hash  slot  for  the  socket,  the
              "local_address"  is  the  local  address  and  protocol  number  pair.  "St" is the
              internal status of the socket.  The "tx_queue" and "rx_queue" are the outgoing  and
              incoming  data  queue  in  terms of kernel memory usage.  The "tr", "tm->when", and
              "rexmits" fields are not used by RAW.  The "uid" field holds the effective  UID  of
              the creator of the socket.

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

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

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

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

       /proc/net/unix
              Lists the UNIX domain sockets present within the  system  and  their  status.   The
              format is:

              Num RefCount Protocol Flags    Type St Inode Path
               0: 00000002 00000000 00000000 0001 03    42
               1: 00000001 00000000 00010000 0001 01  1948 /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.

              Inode:    the inode number of the socket.

              Path:     the bound pathname (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 queueing, 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 information.

              (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 always 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 initialization  and  their
              configuration.

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

       /proc/profile (since Linux 2.4)
              This  file is present only if the kernel was booted with the profile=1 command-line
              option.  It exposes kernel profiling information in a  binary  format  for  use  by
              readprofile(1).   Writing (e.g., an empty string) to this file resets the profiling
              counters; 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  subsystem  or  switch
              certain features on or off.

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

              The command

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

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

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

              Reading these files will usually show driver and  host  configuration,  statistics,
              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 entries 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)
                            (6) Time servicing interrupts.

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

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

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

                     guest_nice (since Linux 2.6.33)
                            (10)  Time  spent  running  a  niced  guest  (virtual  CPU  for guest
                            operating systems under the control of the Linux kernel).

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

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

              intr 1462898
                     This  line  shows counts of interrupts serviced since boot time, for each of
                     the possible system interrupts.  The  first  column  is  the  total  of  all
                     interrupts  serviced  including unnumbered architecture specific interrupts;
                     each subsequent column is the total for that particular numbered  interrupt.
                     Unnumbered interrupts are not shown, only summed into the total.

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

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

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

              processes 86031
                     Number of forks since boot.

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

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

              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 subsequent 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 in  some  cases
              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  integer  or  long  values,  these  may  be
              separated by any of the following whitespace characters: ' ', '\t', or '\n'.  Using
              other separators leads to the error EINVAL.

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

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

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

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

       /proc/sys/fs/aio-max-nr and /proc/sys/fs/aio-nr (since Linux 2.6.4)
              aio-nr  is the running total of the number of events specified by io_setup(2) calls
              for all  currently  active  AIO  contexts.   If  aio-nr  reaches  aio-max-nr,  then
              io_setup(2) will fail with the error EAGAIN.  Raising aio-max-nr does not result in
              the preallocation or resizing of any kernel data structures.

       /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 requested by system) and two dummy values.

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

              * nr_unused is the number of unused dentries.

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

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

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

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

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

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

       /proc/sys/fs/file-max
              This  file  defines  a  system-wide  limit  on  the  number  of  open files for all
              processes.  System calls that fail when encountering this limit fail with the error
              ENFILE.   (See  also  setrlimit(2),  which can be used by a process to set the per-
              process limit, RLIMIT_NOFILE, on the number of files it may open.)  If you get lots
              of  error  messages  in the kernel log about running out of file handles (open file
              descriptions) (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 allocated file handles
              (i.e., the number of open file descriptions; see open(2)); the number of free  file
              handles;  and  the  maximum  number  of  file  handles  (i.e.,  the  same  value as
              /proc/sys/fs/file-max).  If the number of allocated file handles is  close  to  the
              maximum,  you should consider increasing the maximum.  Before Linux 2.6, the kernel
              allocated file handles dynamically, but it didn't free  them  again.   Instead  the
              free  file  handles  were  kept in a list for reallocation; the "free file handles"
              value indicates the size of that  list.   A  large  number  of  free  file  handles
              indicates  that  there  was  a  past peak in the usage of open file handles.  Since
              Linux 2.6, the kernel does deallocate  freed  file  handles,  and  the  "free  file
              handles" value is always zero.

       /proc/sys/fs/inode-max (only present until Linux 2.2)
              This  file  contains  the maximum number of in-memory inodes.  This value should be
              3–4 times larger than the value  in  file-max,  since  stdin,  stdout  and  network
              sockets  also  need an inode to handle them.  When you regularly run out of inodes,
              you need to increase this value.

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

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

       /proc/sys/fs/inode-state
              This  file  contains  seven numbers: nr_inodes, nr_free_inodes, preshrink, and four
              dummy values (always zero).

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

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

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

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

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

       /proc/sys/fs/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 a 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
              enabled, any UID or GID that would exceed 65535 is translated to the overflow value
              before being written to disk.

       /proc/sys/fs/pipe-max-size (since Linux 2.6.35)
              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_fifos (since Linux 4.19)
              The value in this file is/can be set to one of the following:

              0   Writing to FIFOs is unrestricted.

              1   Don't allow O_CREAT open(2) on FIFOs that the  caller  doesn't  own  in  world-
                  writable  sticky  directories,  unless  the  FIFO  is owned by the owner of the
                  directory.

              2   As for the value 1, but the restriction also applies to  group-writable  sticky
                  directories.

              The  intent  of  the  above  protections  is  to  avoid  unintentional writes to an
              attacker-controlled FIFO when a program expected to create a regular file.

       /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 behavior 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 following 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 credentials(7), a process's filesystem UID is
                 normally the same as its effective UID).

              *  All of the following conditions are true:

                  ·  the target is a regular file;

                  ·  the target file does not have its set-user-ID mode bit enabled;

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

                  ·  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 "pinning" vulnerable  set-user-ID  and  set-group-ID  files
              against being upgraded by the administrator, or linking to special files.

       /proc/sys/fs/protected_regular (since Linux 4.19)
              The value in this file is/can be set to one of the following:

              0   Writing to regular files is unrestricted.

              1   Don't  allow  O_CREAT  open(2)  on regular files that the caller doesn't own in
                  world-writable sticky directories, unless the regular  file  is  owned  by  the
                  owner of the directory.

              2   As  for  the value 1, but the restriction also applies to group-writable sticky
                  directories.

              The intent of the above protections is similar to protected_fifos,  but  allows  an
              application  to  avoid  writes  to  an  attacker-controlled regular file, where the
              application expected to create one.

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

              1 ("debug")
                     All processes dump  core  when  possible.   (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 processes.

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

                     Additionally,  since Linux 3.6, /proc/sys/kernel/core_pattern must either be
                     an absolute pathname or a pipe command, 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  parameters,  as
              described below.

       /proc/sys/kernel/acct
              This file contains three numbers: highwater, lowwater, and frequency.  If BSD-style
              process accounting is enabled, these values control its behavior.  If free space on
              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 recomputing 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).   Echoing  "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 (because  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 execve(2).  Starting with Linux 2.6.25, the  system-wide  capability
              bounding  set  disappeared,  and  was  replaced  by  a per-thread bounding set; see
              capabilities(7).

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

       /proc/sys/kernel/core_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 keyboard.  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, without even syncing its
              dirty buffers.  Note: when a program (like dosemu) has the keyboard in "raw"  mode,
              the  ctrl-alt-del  is  intercepted by the program before it ever reaches the kernel
              tty layer, and it's up to the program to decide what to do with it.

       /proc/sys/kernel/dmesg_restrict (since Linux 2.6.37)
              The value in this file determines who can see kernel syslog contents.  A value of 0
              in this file imposes no restrictions.  If the value is 1, only privileged users can
              read the kernel syslog.  (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 hostname  "darkstar"  and
              DNS  (Internet  Domain  Name Server) domainname "frop.org", not to be confused with
              the NIS (Network Information Service) or YP (Yellow Pages) domainname.   These  two
              domain  names  are  in  general  different.   For  a  detailed  discussion  see the
              hostname(1) man page.

       /proc/sys/kernel/hotplug
              This file contains the pathname 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 PowerPC 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 described 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.  Enabled if nonzero.

       /proc/sys/kernel/modprobe
              This file contains the pathname 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 CONFIG_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 message 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 autoreboot after this number of seconds.  When you use the software watchdog
              device driver, the recommended setting is 60.

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

       /proc/sys/kernel/pid_max (since Linux 2.5.34)
              This  file  specifies  the value at which PIDs wrap around (i.e., the value in this
              file is one greater than the maximum PID).  PIDs greater than this  value  are  not
              allocated;  thus,  the  value  in this file also acts as a system-wide limit on the
              total number 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 currently in use.

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

       /proc/sys/kernel/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
              Documentation/admin-guide/initrd.rst   (or  Documentation/initrd.txt  before  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 rebooting?

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

       /proc/sys/kernel/rtsig-nr
              (Only  in  kernels up to and including 2.6.7.)  This file shows the number 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 configuration.  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  possible  to  create  shared  memory  segments  that  exist
              independently of any attached process.

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

              Setting this file to 1 provides a way of ensuring that all System 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 nonstandard 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
              1 GB 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 overwrite 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  buffer  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
              specifically enable it at run-time, but this is not the case any  more).   Possible
              values in this file are:

              0    Disable sysrq completely

              1    Enable all functions of sysrq

              > 1  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 configuration option is
              enabled.    For   further   details   see   the   Linux    kernel    source    file
              Documentation/admin-guide/sysrq.rst (or Documentation/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 maximum value that can be written  is
              given  by  the  constant  FUTEX_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,  buffer  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 system 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 provide 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 application 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 possible.  The effect of this action can be
              seen by examining /proc/buddyinfo.

              Present only if the kernel was configured with CONFIG_COMPACTION.

       /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  performing  reproducible  filesystem  benchmarks.   Because
              writing  to  this  file  causes  the benefits of caching to be lost, it can degrade
              overall system performance.

              To free pagecache, use:

                  echo 1 > /proc/sys/vm/drop_caches

              To free dentries and inodes, use:

                  echo 2 > /proc/sys/vm/drop_caches

              To free pagecache, dentries and inodes, use:

                  echo 3 > /proc/sys/vm/drop_caches

              Because writing to this file is a nondestructive operation and  dirty  objects  are
              not freeable, the user should run sync(1) first.

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

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

              The file has one of the following values:

              1:  Kill  all  processes  that have the corrupted-and-not-reloadable page mapped as
                  soon as the corruption is detected.  Note 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 advanced machine  check
              handling and depends on the hardware capabilities.

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

              Present only if the kernel was configured with CONFIG_MEMORY_FAILURE.

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

              1:  Attempt recovery.

              0:  Always panic on a memory failure.

              Present only if the kernel was configured with CONFIG_MEMORY_FAILURE.

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

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

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

              The default value is 0.

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

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

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

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

              The default value is 0.

       /proc/sys/vm/overcommit_kbytes (since Linux 3.14)
              This  writable  file  provides  an alternative to /proc/sys/vm/overcommit_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 CommitLimit 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 getting 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 arrays.  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/overcommit_ratio; and

                   *  total_swap is the amount of swap space.

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

              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/admin_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 situation.

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

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

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

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

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

       /proc/sys/vm/user_reserve_kbytes (since Linux 3.10)
              Specifies  an  amount  of  memory  (in KiB) to reserve for user processes.  This is
              intended to prevent a user from starting a single 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_reserve_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  application  requests
              memory.

       /proc/sys/vm/unprivileged_userfaultfd (since Linux 5.2)
              This  (writable)  file  exposes a flag that controls whether unprivileged processes
              are allowed to  employ  userfaultfd(2).   If  this  file  has  the  value  1,  then
              unprivileged  processes may use userfaultfd(2).  If this file has the value 0, then
              only processes that have the CAP_SYS_PTRACE capability may  employ  userfaultfd(2).
              The default value in this file is 1.

       /proc/sysrq-trigger (since Linux 2.4.21)
              Writing  a  character  to this file triggers the same SysRq function as typing ALT-
              SysRq-<character> (see the description of /proc/sys/kernel/sysrq).   This  file  is
              normally  writable  only  by root.  For further details see the Linux kernel source
              file Documentation/admin-guide/sysrq.rst (or Documentation/sysrq.txt  before  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 understanding.  sysvipc(7)
              provides further background on the information shown by these files.

       /proc/thread-self (since Linux 3.17)
              This directory refers  to  the  thread  accessing  the  /proc  filesystem,  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 parameters 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 facility and to read
              out the sampled information.

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

                  # echo 1 > /proc/timer_stats

              The following command stops a sampling period:

                  # echo 0 > /proc/timer_stats

              The statistics can be retrieved by:

                  $ cat /proc/timer_stats

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

              Sample output from /proc/timer_stats:

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

              The output columns are:

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

              *  the PID of the process that initialized the timer;

              *  the name of the process that initialized the timer;

              *  the function where the timer was initialized; and

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

              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 information 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  (values  in  seconds): the uptime of the system
              (including time spent in suspend) and the amount of time spent in the idle process.

       /proc/version
              This string identifies the kernel version that is currently running.   It  includes
              the    contents   of   /proc/sys/kernel/ostype,   /proc/sys/kernel/osrelease,   and
              /proc/sys/kernel/version.  For example:

                  Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994

       /proc/vmstat (since Linux 2.6.0)
              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 configured with suitable options.  (In  some  cases,
              the  options  required 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/admin-guide/mm/transhuge.rst.

              compact_fail (since Linux 2.6.35)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              compact_success (since Linux 2.6.35)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              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/admin-guide/mm/transhuge.rst.

              thp_fault_fallback (since Linux 2.6.39)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              thp_collapse_alloc (since Linux 2.6.39)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              thp_collapse_alloc_failed (since Linux 2.6.39)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              thp_split (since Linux 2.6.39)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              thp_zero_page_alloc (since Linux 3.8)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              thp_zero_page_alloc_failed (since Linux 3.8)
                     See the kernel source file Documentation/admin-guide/mm/transhuge.rst.

              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  displays  information about memory zones.  This is useful for analyzing
              virtual memory behavior.

NOTES

       Many files contain strings (e.g., the environment  and  command  line)  that  are  in  the
       internal  format,  with  subfields  terminated by null bytes ('\0').  When inspecting such
       files, you may find that the results are more  readable  if  you  use  a  command  of  the
       following form to display them:

           $ cat file | tr '\000' '\n'

       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), htop(1), init(1), ps(1), pstree(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,
       Documentation/sysctl/fs.txt,                              Documentation/sysctl/kernel.txt,
       Documentation/sysctl/net.txt, and Documentation/sysctl/vm.txt.

COLOPHON

       This  page  is  part of release 5.10 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/.