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

NAME
       proc - process information pseudo-filesystem

DESCRIPTION
       The  proc  filesystem  is  a  pseudo-filesystem which provides an interface to kernel data
       structures.  It is commonly mounted at /proc.  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, al-
       lowing 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 be-
                  havior, and the default if this mount option is not specified.

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

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

              Underneath each of the /proc/[pid] directories, a task subdirectory contains subdi-
              rectories  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 get-
              dents(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  infor-
              mation  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 (de-
                 scribed 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"  at-
              tribute 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-re-
              lated  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 pur-
              pose 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  ex-
              ecve(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  ex-
              plicitly reset.  In SELinux, a process can set only its own /proc/[pid]/attr/fscre-
              ate 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  Documenta-
              tion/security/keys.txt on Linux between 3.0 and 4.13, or Documentation/keys.txt be-
              fore 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 as-
                     sociated 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 ap-
              proximately 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  AC-
              CESSED/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 inspect-
              ing 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 cur-
                     rent 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  opera-
              tions,  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  execut-
              ing  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  environ-
              ment 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 path-
              name of the executed command.  This symbolic link can be dereferenced normally; at-
              tempting 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 re-
              turns a string in the format:

                  type:[inode]

              For example, socket:[2248868] will be a socket and its inode is 2248868.  For sock-
              ets,  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  pro-
              duced  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, as-
              suming 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 com-
              mand above could be written as:

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

              Permission  to  dereference or read (readlink(2)) the symbolic links in this direc-
              tory 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 de-
              scriptor  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  in-
              formation 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  contain-
                     ing this file.  See the description of /proc/[pid]/mountinfo.

              For eventfd file descriptors (see eventfd(2)), we see (since Linux 3.8) the follow-
              ing 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 moni-
              tored 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 fol-
              lowing 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 follow-
              ing 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  ex-
              posed  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  fol-
              lowing 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 hexadeci-
                     mal).

              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  hexadeci-
                     mal).

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

              For  timerfd  file descriptors (see timerfd(2)), we see (since Linux 3.17) the fol-
              lowing 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, ex-
                     pressed in seconds and nanoseconds.  This is always expressed as a  relative
                     value,  regardless  of whether the timer was created using the TFD_TIMER_AB-
                     STIME 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_get-
                     time(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  unaf-
                     fected  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 hap-
                     pen, 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_RE-
              STORE kernel configuration option was enabled.

              Capabilities are required to read the contents of the symbolic links in this direc-
              tory:  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:mi-
              nor);  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 se-
              quence.

              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_AT-
              TACH_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 ch-
                   root(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  di-
                   rectory, 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 un-
              bindable.  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/sharedsub-
              tree.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  name-
              space  (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 se-
              lect(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 de-
                   vice).

              (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 al-
              lowed 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.  Fi-
              nally, 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 de-
              termine 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/ad-
                     min-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/kpage-
                     count.  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  personal-
              ity(2).  The value is displayed in hexadecimal notation.

              Permission  to access this file is governed by a ptrace access mode PTRACE_MODE_AT-
              TACH_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  con-
              tents 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  propor-
              tional 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.  "Ref-
              erenced" 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 mem-
              ory  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_PRO-
              TECTION_KEYS configuration option (since Linux 4.6).

              The  "VmFlags" line (available since Linux 3.8) represents the kernel flags associ-
              ated 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_STACK-
              TRACE configuration option.

              Permission  to access this file is governed by a ptrace access mode PTRACE_MODE_AT-
              TACH_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 be-
              low.  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  con-
                     tained in the combination of bits 31 to 20 and 7 to 0; the major device num-
                     ber 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_* de-
                     fines 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 applica-
                     tions 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 run-
                     ning 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 sched-
                     uling priority, minus one; that is, a number in the range -2 to -100, corre-
                     sponding  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 ex-
                     pressed 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, be-
                     cause   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, be-
                     cause   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, be-
                     cause   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,  be-
                     cause   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 op-
                     erating 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 opti-
              mization.   If   accurate   values   are   required,   use   /proc/[pid]/smaps   or
              /proc/[pid]/smaps_rollup  instead,  which are much slower but provide accurate, de-
              tailed 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) charac-
                     ters (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  name-
                     space  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  NSt-
                     gid.  (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  inac-
                     curate; see /proc/[pid]/statm above.

              RssFile
                     Size  of  resident file mappings.  (since Linux 4.5).  This value is inaccu-
                     rate; 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  sig-
                     nals 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 re-
                     source  limit  on the number of queued signals for this process (see the de-
                     scription 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 capa-
                     bilities(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 SEC-
                     COMP_MODE_DISABLED; 1 means SECCOMP_MODE_STRICT; 2  means  SECCOMP_MODE_FIL-
                     TER.   This  field  is  provided  only if the kernel was built with the CON-
                     FIG_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_TRACE-
              HOOK.

              Permission  to access this file is governed by a ptrace access mode PTRACE_MODE_AT-
              TACH_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] subdirecto-
              ries will be the same as in the corresponding file in the parent /proc/[pid] direc-
              tory (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  dis-
              tinct  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  differ-
              ent 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  reli-
              ably  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_CHECK-
              POINT_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 fol-
                     lowed by a slash, and then the sigev_value value supplied to the signal han-
                     dler.  Valid only for timers that notify via a signal.

              notify The  part  before  the slash specifies the mechanism that this timer uses to
                     deliver notifications, and is one of "thread", "signal", or "none".  Immedi-
                     ately  following  the  slash  is  either  the  string  "tid" for timers with
                     SIGEV_THREAD_ID notification, or "pid" for timers that notify by other mech-
                     anisms.   Following  the "." is the PID of the process (or the kernel thread
                     ID of the thread)  that will be delivered a signal if the timer delivers no-
                     tifications via a signal.

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

              This  file  is  available  only  when  the kernel was configured with CONFIG_CHECK-
              POINT_RESTORE.

       /proc/[pid]/timerslack_ns (since Linux 4.6)
              This file exposes the process's "current" timer slack value, expressed in  nanosec-
              onds.   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  ca-
              pability 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 con-
              tains 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 de-
              fined 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  sat-
              isfy  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  differ-
              ent  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 set-
              pci(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_IKCON-
              FIG_PROC.

       /proc/crypto
              A list of the ciphers provided by the kernel crypto API.  For details, see the ker-
              nel Linux Kernel Crypto API documentation available under the kernel source  direc-
              tory 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 sup-
              ported architecture a different list.  Two common entries are processor which gives
              CPU  number  and  bogomips; a system constant that is calculated during kernel ini-
              tialization.  SMP machines have information for each  CPU.   The  lscpu(1)  command
              gathers its information from this file.

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

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

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

       /proc/driver
              Empty subdirectory.

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

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

       /proc/filesystems
              A  text  listing  of  the  filesystems  which  are  supported by the kernel, namely
              filesystems which were compiled into the kernel or whose kernel  modules  are  cur-
              rently 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  inter-
              rupts  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 Docu-
              mentation/admin-guide/mm/pagemap.rst.  Before kernel 2.6.29, KPF_WRITEBACK, KPF_RE-
              CLAIM, 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  up-
              time(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  sched-
              uling  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  dis-
                  played 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  fil-
              tering 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 pa-
              rameter,  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.  Ex-
              cept  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 ker-
                     nel 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 tremen-
                     dously large (20 MB or so).

              Cached %lu
                     In-memory cache for files read from the disk (the page cache).  Doesn't  in-
                     clude 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 ab-
                     solutely necessary.

              Inactive %lu
                     Memory  which  has  been  less recently used.  It is more eligible to be re-
                     claimed 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 mem-
                     ory 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 ad-
                     dress 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/vmal-
                     locinfo.

              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 alloca-
                     tion has yet been made.  These reserved huge pages guarantee that an  appli-
                     cation  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  Documenta-
              tion/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  resolu-
              tions.   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 hard-
              ware 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 sta-
              tus.  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 "lo-
              cal_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 in-
              formation 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  "lo-
              cal_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 "lo-
              cal_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 for-
              mat 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 name-
                        space 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-ex-
                   tensions(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 ap-
                   plication.

              (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)  monotoni-
                   cally 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  CON-
              FIG_PCI_OLD_PROC set at kernel compilation).  It became once more nonoptionally en-
              abled  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 cer-
              tain 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,  bus-
              logic,  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 reg-
              istered host.  Every host-file is named after the number the host was assigned dur-
              ing 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 identi-
              cal 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 var-
                     ious 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 cal-
                               culate.

                            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 un-
                            der the control of the Linux kernel.

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

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

              swap 1 0
                     The number of swap pages that have been brought in and 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 inter-
                     rupts serviced including unnumbered architecture specific  interrupts;  each
                     subsequent  column is the total for that particular numbered interrupt.  Un-
                     numbered 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_writ-
                     ten)
                     (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 on-
                     ward.)

              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 sepa-
              rated 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   Documenta-
              tion/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  fc-
              ntl(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  pro-
              cesses.   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 indi-
              cates 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 sock-
              ets 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 repre-
              sents 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 en-
              abled, any UID or GID that would exceed 65535 is translated to the  overflow  value
              before being written to disk.

       /proc/sys/fs/pipe-max-size (since Linux 2.6.35)
              See pipe(7).

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

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

       /proc/sys/fs/protected_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  di-
                  rectory.

              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  at-
              tacker-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:

                  o  the target is a regular file;

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

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

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

              The  default value in this file is 0.  Setting the value to 1 prevents a longstand-
              ing 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  ap-
              plication 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 restric-
              tions 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  circum-
              stances  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 se-
                     teuid(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 never-
                     theless 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 priv-
                     ileged 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 admin-
                     istrators 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 de-
              scribed 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 deter-
              mines 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 name-
              space creation/removal.  Echoing "1" into this file enabled msgmni automatic recom-
              puting (and triggered a recomputation of msgmni based  on  the  current  amount  of
              available memory and number of IPC namespaces).  Echoing "0" disabled automatic re-
              computing.  (Automatic recomputing was also disabled if a value was explicitly  as-
              signed 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  capa-
              bilities(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  han-
              dle 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  host-
              name(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 re-
              placed 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 ze-
              ros 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  CON-
              FIG_MODULES  (CONFIG_KMOD  in  Linux 2.6.26 and earlier) option enabled.  It is de-
              scribed 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 modu-
              lar 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 op-
              tion 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 max-
              imum 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/over-
              flowuid.

       /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 out-
              put) 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 to-
              tal  number  of processes and threads.  The default value for this file, 32768, re-
              sults 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  powersav-
              ing, 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  ar-
              chitectures 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  random-
                 ized.   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/ad-
              min-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  out-
              standing 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 sec-
              comp(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  inde-
              pendently 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 de-
              stroyed 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 de-
              scription 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  seg-
              ments 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 up-
              dating 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 de-
                  scriptor 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 en-
                  tries 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 de-
              fault, 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/ad-
              min-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 min-
              imum 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 struc-
              tures  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  man-
              agement.

       /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_mem-
              ory) 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 mem-
              ory.

       /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 ap-
              plications.  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 actu-
              ally 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  situa-
              tions.

              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  al-
              lows  for finer-grained control of CommitLimit on systems with extremely large mem-
              ory sizes.

              Only one of overcommit_kbytes or overcommit_ratio can have an effect:  if  overcom-
              mit_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 em-
              ploy 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  dedi-
              cated  to  huge  pages,  and  an overcommit_ratio of 50, this formula yields a Com-
              mitLimit 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/overcom-
              mit_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 ac-
              cording 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 in-
              tended 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]  ex-
              pressed 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  mem-
              ory.

       /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  unprivi-
              leged  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 simi-
              lar 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  identi-
              cal  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 develop-
              ers  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 collec-
              tion 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 up-
              dated 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 (in-
              cluding 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  con-
              tains  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  op-
              tions  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 inter-
       nal  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,   Documenta-
       tion/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/.

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