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NAME

       proc - process information pseudo-filesystem

DESCRIPTION

       The  proc filesystem is a pseudo-filesystem which provides an interface to kernel data structures.  It is
       commonly mounted at /proc.  Typically, it is mounted automatically by the system,  but  it  can  also  be
       mounted manually using a command such as:

           mount -t proc proc /proc

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

   Mount options
       The proc filesystem supports the following mount options:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       All of the above are described in more detail below.

   Files and directories
       The following list provides details of many of the files and directories under the /proc hierarchy.

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

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

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

              The process's "dumpable" attribute may change for the following reasons:

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

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

              Resetting the "dumpable" attribute to 1 reverts the ownership of the /proc/[pid]/*  files  to  the
              process's  effective UID and GID.  Note, however, that if the effective UID or GID is subsequently
              modified, then the "dumpable" attribute may be reset, as described in prctl(2).  Therefore, it may
              be  desirable  to reset the "dumpable" attribute after making any desired changes to the process's
              effective UID or GID.

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

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

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

              In SELinux, this file is used to get the security context of a process.  Prior  to  Linux  2.6.11,
              this file could not be used to set the security context (a write was always denied), since SELinux
              limited process security transitions to execve(2) (see the description  of  /proc/[pid]/attr/exec,
              below).  Since Linux 2.6.11, SELinux lifted this restriction and began supporting "set" operations
              via writes to this node if authorized by policy, although use of this operation is  only  suitable
              for  applications  that  are  trusted  to  maintain any desired separation between the old and new
              security contexts.

              Prior to Linux 2.6.28, SELinux did not allow threads within a multithreaded process to  set  their
              security  context  via this node as it would yield an inconsistency among the security contexts of
              the threads sharing the same memory space.  Since Linux 2.6.28, SELinux  lifted  this  restriction
              and  began  supporting  "set"  operations  for  threads  within a multithreaded process if the new
              security context is bounded by the old security context, where the bounded relation is defined  in
              policy  and  guarantees  that  the new security context has a subset of the permissions of the old
              security context.

              Other security modules may choose to support "set" operations via writes to this node.

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

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

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

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

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

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

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

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

       /proc/[pid]/auxv (since 2.6.0)
              This contains the contents of the ELF interpreter information passed to the process at exec  time.
              The  format  is  one unsigned long ID plus one unsigned long value for each entry.  The last entry
              contains two zeros.  See also getauxval(3).

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

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

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

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

              The following values may be written to the file:

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

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

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

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

              Further values can be written to affect different properties:

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

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

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

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

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

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

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

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

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

              This file provides a superset of the prctl(2)  PR_SET_NAME  and  PR_GET_NAME  operations,  and  is
              employed by pthread_setname_np(3) when used to rename threads other than the caller.  The value in
              this file is used for the %e specifier in /proc/sys/kernel/core_pattern; see core(5).

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

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

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

                  $ cd /proc/20/cwd; pwd -P

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

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

       /proc/[pid]/environ
              This  file  contains the initial environment that was set when the currently executing program was
              started via execve(2).  The entries are separated by null bytes ('\0'), and there may  be  a  null
              byte at the end.  Thus, to print out the environment of process 1, you would do:

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

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

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

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

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

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

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

                  [device]:inode

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

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

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

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

                  type:[inode]

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

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

                  anon_inode:<file-type>

              In many cases (but not all), the file-type is surrounded by square brackets.

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

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

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

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

              and you have a working filter.

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

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

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

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

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

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

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

       /proc/[pid]/fdinfo/ (since Linux 2.6.22)
              This is a subdirectory containing one entry for each file which the process has open, named by its
              file descriptor.  The files in this directory are readable only by the owner of the process.   The
              contents  of  each file can be read to obtain information about the corresponding file descriptor.
              The content depends on the type of file referred to by the corresponding file descriptor.

              For regular files and directories, we see something like:

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

              The fields are as follows:

              pos    This is a decimal number showing the file offset.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              wd     A watch descriptor number (in decimal).

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

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

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

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

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

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

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

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

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

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

              mflags The flags associated with the mark (expressed in hexadecimal).

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

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

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

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

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

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

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

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

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

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

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

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

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

              The fields are as follows:

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

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

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

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

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

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

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

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

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

       /proc/[pid]/limits (since Linux 2.6.24)
              This  file displays the soft limit, hard limit, and units of measurement for each of the process's
              resource limits (see getrlimit(2)).  Up to and including Linux 2.6.35, this file is  protected  to
              allow  reading  only by the real UID of the process.  Since Linux 2.6.36, this file is readable by
              all users on the system.

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

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

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

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

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

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

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

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

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

              The format of the file is:

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

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

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

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

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

              There are additional helpful pseudo-paths:

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

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

              [vdso] The virtual dynamically linked shared object.  See vdso(7).

              [heap] The process's heap.

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

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

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

              Under Linux 2.0, there is no field giving pathname.

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

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

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

              The file contains lines of the form:

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

              The numbers in parentheses are labels for the descriptions below:

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

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

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

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

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

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

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

              (6)  mount options: per-mount options (see mount(2)).

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

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

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

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

              (11) super options: per-superblock options (see mount(2)).

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

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

       /proc/[pid]/mounts (since Linux 2.4.19)
              This  file  lists  all  the  filesystems  currently  mounted in the process's mount namespace (see
              mount_namespaces(7)).  The format of this file is documented in fstab(5).

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

       /proc/[pid]/mountstats (since Linux 2.6.17)
              This  file  exports  information (statistics, configuration information) about the mount points in
              the process's mount namespace (see mount_namespaces(7)).  Lines in this file have the form:

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

              The fields in each line are:

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

              (2)  The mount point within the filesystem tree.

              (3)  The filesystem type.

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

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

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

       /proc/[pid]/ns/ (since Linux 3.0)
              This  is a subdirectory containing one entry for each namespace that supports being manipulated by
              setns(2).  For more information, see namespaces(7).

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

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

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

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

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

              * whether the process is privileged (-).

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

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

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

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

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

              The oom_score also reflects the adjustment specified by the oom_score_adj or oom_adj  setting  for
              the process.

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

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

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

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

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

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

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

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

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

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

              63     If set, the page is present in RAM.

              62     If set, the page is in swap space

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

              60–57 (since Linux 3.11)
                     Zero

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

              55 (since Linux 3.11)
                     PTE is soft-dirty (see the kernel source file Documentation/admin-guide/mm/soft-dirty.rst).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       /proc/[pid]/smaps (since Linux 2.6.14)
              This  file  shows  memory  consumption  for  each of the process's mappings.  (The pmap(1) command
              displays similar information, in a form that may be easier for parsing.)  For each  mapping  there
              is a series of lines such as the following:

                  00400000-0048a000 r-xp 00000000 fd:03 960637       /bin/bash
                  Size:                552 kB
                  Rss:                 460 kB
                  Pss:                 100 kB
                  Shared_Clean:        452 kB
                  Shared_Dirty:          0 kB
                  Private_Clean:         8 kB
                  Private_Dirty:         0 kB
                  Referenced:          460 kB
                  Anonymous:             0 kB
                  AnonHugePages:         0 kB
                  ShmemHugePages:        0 kB
                  ShmemPmdMapped:        0 kB
                  Swap:                  0 kB
                  KernelPageSize:        4 kB
                  MMUPageSize:           4 kB
                  KernelPageSize:        4 kB
                  MMUPageSize:           4 kB
                  Locked:                0 kB
                  ProtectionKey:         0
                  VmFlags: rd ex mr mw me dw

              The  first  of  these  lines  shows  the  same  information  as  is  displayed  for the mapping in
              /proc/[pid]/maps.  The following lines show the size of the mapping, the  amount  of  the  mapping
              that  is  currently  resident  in  RAM  ("Rss"),  the process's proportional share of this mapping
              ("Pss"), the number of clean and dirty shared pages in the mapping, and the number  of  clean  and
              dirty  private pages in the mapping.  "Referenced" indicates the amount of memory currently marked
              as referenced or accessed.  "Anonymous" shows the amount of memory that does  not  belong  to  any
              file.  "Swap" shows how much would-be-anonymous memory is also used, but out on swap.

              The  "KernelPageSize"  line  (available since Linux 2.6.29) is the page size used by the kernel to
              back the virtual memory area.  This matches the size used by the MMU in  the  majority  of  cases.
              However,  one  counter-example occurs on PPC64 kernels whereby a kernel using 64 kB as a base page
              size may still use 4 kB pages for the MMU on older processors.  To distinguish the two attributes,
              the "MMUPageSize" line (also available since Linux 2.6.29) reports the page size used by the MMU.

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

              The  "ProtectionKey"  line (available since Linux 4.9, on x86 only) contains the memory protection
              key (see pkeys(7)) associated with the virtual memory area.  This entry is  present  only  if  the
              kernel  was  built  with  the  CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS configuration option (since
              Linux 4.6).

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

                  rd  - readable
                  wr  - writable
                  ex  - executable
                  sh  - shared
                  mr  - may read
                  mw  - may write
                  me  - may execute
                  ms  - may share
                  gd  - stack segment grows down
                  pf  - pure PFN range
                  dw  - disabled write to the mapped file
                  lo  - pages are locked in memory
                  io  - memory mapped I/O area
                  sr  - sequential read advise provided
                  rr  - random read advise provided
                  dc  - do not copy area on fork
                  de  - do not expand area on remapping
                  ac  - area is accountable
                  nr  - swap space is not reserved for the area
                  ht  - area uses huge tlb pages
                  sf  - perform synchronous page faults (since Linux 4.15)
                  nl  - non-linear mapping (removed in Linux 4.0)
                  ar  - architecture specific flag
                  wf  - wipe on fork (since Linux 4.14)
                  dd  - do not include area into core dump
                  sd  - soft-dirty flag (since Linux 3.13)
                  mm  - mixed map area
                  hg  - huge page advise flag
                  nh  - no-huge page advise flag
                  mg  - mergeable advise flag
                  um  - userfaultfd missing pages tracking (since Linux 4.3)
                  uw  - userfaultfd wprotect pages tracking (since Linux 4.3)

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

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

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

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

              The  fields, in order, with their proper scanf(3) format specifiers, are listed below.  Whether or
              not certain of these fields display  valid  information  is  governed  by  a  ptrace  access  mode
              PTRACE_MODE_READ_FSCREDS | PTRACE_MODE_NOAUDIT  check  (refer  to ptrace(2)).  If the check denies
              access, then the field value is displayed as 0.   The  affected  fields  are  indicated  with  the
              marking [PT].

              (1) pid  %d
                     The process ID.

              (2) comm  %s
                     The  filename  of  the  executable, in parentheses.  Strings longer than TASK_COMM_LEN (16)
                     characters (including the terminating null byte) are silently truncated.  This  is  visible
                     whether or not the executable is swapped out.

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

                     R  Running

                     S  Sleeping in an interruptible wait

                     D  Waiting in uninterruptible disk sleep

                     Z  Zombie

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

                     t  Tracing stop (Linux 2.6.33 onward)

                     W  Paging (only before Linux 2.6.0)

                     X  Dead (from Linux 2.6.0 onward)

                     x  Dead (Linux 2.6.33 to 3.13 only)

                     K  Wakekill (Linux 2.6.33 to 3.13 only)

                     W  Waking (Linux 2.6.33 to 3.13 only)

                     P  Parked (Linux 3.9 to 3.13 only)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              (45) start_data  %lu  (since Linux 3.3)  [PT]
                     Address above which program initialized and uninitialized (BSS) data are placed.

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

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

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

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

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

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

              (52) exit_code  %d  (since Linux 3.5)  [PT]
                     The thread's exit status in the form reported by waitpid(2).

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

                  size       (1) total program size
                             (same as VmSize in /proc/[pid]/status)
                  resident   (2) resident set size
                             (inaccurate; same as VmRSS in /proc/[pid]/status)
                  shared     (3) number of resident shared pages
                             (i.e., backed by a file)
                             (inaccurate; same as RssFile+RssShmem in
                             /proc/[pid]/status)
                  text       (4) text (code)
                  lib        (5) library (unused since Linux 2.6; always 0)
                  data       (6) data + stack
                  dt         (7) dirty pages (unused since Linux 2.6; always 0)

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

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

                  $ cat /proc/$$/status
                  Name:   bash
                  Umask:  0022
                  State:  S (sleeping)
                  Tgid:   17248
                  Ngid:   0
                  Pid:    17248
                  PPid:   17200
                  TracerPid:      0
                  Uid:    1000    1000    1000    1000
                  Gid:    100     100     100     100
                  FDSize: 256
                  Groups: 16 33 100
                  NStgid: 17248
                  NSpid:  17248
                  NSpgid: 17248
                  NSsid:  17200
                  VmPeak:     131168 kB
                  VmSize:     131168 kB
                  VmLck:           0 kB
                  VmPin:           0 kB
                  VmHWM:       13484 kB
                  VmRSS:       13484 kB
                  RssAnon:     10264 kB
                  RssFile:      3220 kB
                  RssShmem:        0 kB
                  VmData:      10332 kB
                  VmStk:         136 kB
                  VmExe:         992 kB
                  VmLib:        2104 kB
                  VmPTE:          76 kB
                  VmPMD:          12 kB
                  VmSwap:          0 kB
                  HugetlbPages:          0 kB        # 4.4
                  CoreDumping:   0                       # 4.15
                  Threads:        1
                  SigQ:   0/3067
                  SigPnd: 0000000000000000
                  ShdPnd: 0000000000000000
                  SigBlk: 0000000000010000
                  SigIgn: 0000000000384004
                  SigCgt: 000000004b813efb
                  CapInh: 0000000000000000
                  CapPrm: 0000000000000000
                  CapEff: 0000000000000000
                  CapBnd: ffffffffffffffff
                  CapAmb:   0000000000000000
                  NoNewPrivs:     0
                  Seccomp:        0
                  Speculation_Store_Bypass:       vulnerable
                  Cpus_allowed:   00000001
                  Cpus_allowed_list:      0
                  Mems_allowed:   1
                  Mems_allowed_list:      0
                  voluntary_ctxt_switches:        150
                  nonvoluntary_ctxt_switches:     545

              The fields are as follows:

              Name   Command  run by this process.  Strings longer than TASK_COMM_LEN (16) characters (including
                     the terminating null byte) are silently truncated.

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

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

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

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

              Pid    Thread ID (see gettid(2)).

              PPid   PID of parent process.

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

              Uid, Gid
                     Real, effective, saved set, and filesystem UIDs (GIDs).

              FDSize Number of file descriptor slots currently allocated.

              Groups Supplementary group list.

              NStgid Thread  group ID (i.e., PID) in each of the PID namespaces of which [pid] is a member.  The
                     leftmost entry shows the value with respect to  the  PID  namespace  of  the  process  that
                     mounted this procfs (or the root namespace if mounted by the kernel), followed by the value
                     in successively nested inner namespaces.  (Since Linux 4.1.)

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

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

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

              VmPeak Peak virtual memory size.

              VmSize Virtual memory size.

              VmLck  Locked memory size (see mlock(2)).

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

              VmHWM  Peak  resident  set  size  ("high  water   mark").    This   value   is   inaccurate;   see
                     /proc/[pid]/statm above.

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

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

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

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

              VmData, VmStk, VmExe
                     Size  of  data,  stack, and text segments.  This value is inaccurate; see /proc/[pid]/statm
                     above.

              VmLib  Shared library code size.

              VmPTE  Page table entries size (since Linux 2.6.10).

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

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

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

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

              Threads
                     Number of threads in process containing this thread.

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

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

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

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

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

              CapAmb Ambient capability set, expressed in hexadecimal (since Linux 4.3, see capabilities(7)).

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

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

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

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

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

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

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

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

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

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

              This file is present only if the kernel was configured with CONFIG_HAVE_ARCH_TRACEHOOK.

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

       /proc/[pid]/task (since Linux 2.6.0)
              This  is  a  directory that contains one subdirectory for each thread in the process.  The name of
              each subdirectory is the numerical thread ID ([tid]) of the thread (see gettid(2)).

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

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

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

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

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

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

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

              The lines shown for each timer have the following meanings:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

                  (2^order) * PAGE_SIZE

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

              For example on an x86-64 system:
         Node 0, zone     DMA     1    1    1    0    2    1    1    0    1    1    3
         Node 0, zone   DMA32    65   47    4   81   52   28   13   10    5    1  404
         Node 0, zone  Normal   216   55  189  101   84   38   37   27    5    3  587

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

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

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

       /proc/bus
              Contains subdirectories for installed busses.

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

       /proc/bus/pccard/drivers

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

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

       /proc/cgroups (since Linux 2.6.24)
              See cgroups(7).

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

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

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

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

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

       /proc/cpuinfo
              This  is  a  collection  of  CPU  and  system  architecture  dependent  items,  for each supported
              architecture a different list.  Two common entries  are  processor  which  gives  CPU  number  and
              bogomips;  a  system  constant that is calculated during kernel initialization.  SMP machines have
              information for each CPU.  The lscpu(1) command gathers its information from this file.

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

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

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

       /proc/driver
              Empty subdirectory.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              The /proc/kpagecount file is present only if  the  CONFIG_PROC_PAGE_MONITOR  kernel  configuration
              option is enabled.

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

                   0 - KPF_LOCKED
                   1 - KPF_ERROR
                   2 - KPF_REFERENCED
                   3 - KPF_UPTODATE
                   4 - KPF_DIRTY
                   5 - KPF_LRU
                   6 - KPF_ACTIVE
                   7 - KPF_SLAB
                   8 - KPF_WRITEBACK
                   9 - KPF_RECLAIM
                  10 - KPF_BUDDY
                  11 - KPF_MMAP           (since Linux 2.6.31)
                  12 - KPF_ANON           (since Linux 2.6.31)
                  13 - KPF_SWAPCACHE      (since Linux 2.6.31)
                  14 - KPF_SWAPBACKED     (since Linux 2.6.31)
                  15 - KPF_COMPOUND_HEAD  (since Linux 2.6.31)
                  16 - KPF_COMPOUND_TAIL  (since Linux 2.6.31)
                  17 - KPF_HUGE           (since Linux 2.6.31)
                  18 - KPF_UNEVICTABLE    (since Linux 2.6.31)
                  19 - KPF_HWPOISON       (since Linux 2.6.31)
                  20 - KPF_NOPAGE         (since Linux 2.6.31)
                  21 - KPF_KSM            (since Linux 2.6.32)
                  22 - KPF_THP            (since Linux 3.4)
                  23 - KPF_BALLOON        (since Linux 3.18)
                  24 - KPF_ZERO_PAGE      (since Linux 4.0)
                  25 - KPF_IDLE           (since Linux 4.3)

              For  further  details  on  the  meanings   of   these   bits,   see   the   kernel   source   file
              Documentation/admin-guide/mm/pagemap.rst.    Before  kernel  2.6.29,  KPF_WRITEBACK,  KPF_RECLAIM,
              KPF_BUDDY, and KPF_LOCKED did not report correctly.

              The /proc/kpageflags file is present only if  the  CONFIG_PROC_PAGE_MONITOR  kernel  configuration
              option is enabled.

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

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

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

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

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

              The fields shown in each line are as follows:

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

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

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

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

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

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

                  ADVISORY
                         This is an advisory lock.

                  MANDATORY
                         This is a mandatory lock.

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

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

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

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

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

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

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

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

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

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

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

       /proc/meminfo
              This  file  reports  statistics about memory usage on the system.  It is used by free(1) to report
              the amount of free and used memory (both physical and swap) on the system as well  as  the  shared
              memory  and  buffers  used  by  the  kernel.   Each line of the file consists of a parameter name,
              followed by a colon, the value of the parameter, and an option unit of measurement  (e.g.,  "kB").
              The  list  below describes the parameter names and the format specifier required to read the field
              value.  Except as noted below, all of the fields have been present since  at  least  Linux  2.6.0.
              Some  fields  are  displayed  only  if  the  kernel  was  configured  with  various options; those
              dependencies are noted in the list.

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

              MemFree %lu
                     The sum of LowFree+HighFree.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              SwapTotal %lu
                     Total amount of swap space available.

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

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

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

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

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

              Shmem %lu (since Linux 2.6.32)
                     Amount of memory consumed in tmpfs(5) filesystems.

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

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

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

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

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

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

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

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

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

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

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

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

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

              VmallocTotal %lu
                     Total size of vmalloc memory area.

              VmallocUsed %lu
                     Amount of vmalloc area which is used.  Since Linux 4.4, this field is no longer calculated,
                     and is hard coded as 0.  See /proc/vmallocinfo.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       /proc/mounts
              Before kernel 2.4.19, this file was a list of all the filesystems currently mounted on the system.
              With  the  introduction of per-process mount namespaces in Linux 2.4.19 (see mount_namespaces(7)),
              this file became a link to /proc/self/mounts, which lists the mount points of  the  process's  own
              mount namespace.  The format of this file is documented in fstab(5).

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

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

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

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

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

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

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

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

       /proc/net/dev_mcast
              Defined in /usr/src/linux/net/core/dev_mcast.c:

                  indx interface_name  dmi_u dmi_g dmi_address
                  2    eth0            1     0     01005e000001
                  3    eth1            1     0     01005e000001
                  4    eth2            1     0     01005e000001

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

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

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

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

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

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

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

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

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

              The fields are as follows:

              Num:      the kernel table slot number.

              RefCount: the number of users of the socket.

              Protocol: currently always 0.

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

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

              St:       the internal state of the socket.

              Inode:    the inode number of the socket.

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

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

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

              The fields in each line are:

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

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

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

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

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

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

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

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

              The last number exists only for compatibility reasons and is always 1.

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

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

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

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

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

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

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

              The command

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

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

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

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

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

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

       /proc/slabinfo
              Information about kernel caches.  See slabinfo(5) for details.

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

              cpu 10132153 290696 3084719 46828483 16683 0 25195 0 175628 0
              cpu0 1393280 32966 572056 13343292 6130 0 17875 0 23933 0
                     The  amount  of  time,  measured  in  units  of  USER_HZ  (1/100ths  of  a  second  on most
                     architectures, use sysconf(_SC_CLK_TCK) to obtain the right value), that the system  ("cpu"
                     line) or the specific CPU ("cpuN" line) spent in various states:

                     user   (1) Time spent in user mode.

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

                     system (3) Time spent in system mode.

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

                     iowait (since Linux 2.5.41)
                            (5) Time waiting for I/O to complete.  This value is not reliable, for the following
                            reasons:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              processes 86031
                     Number of forks since boot.

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

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

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

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

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

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

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

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

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

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

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

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

       /proc/sys/fs/binfmt_misc
              Documentation  for  files  in  this  directory can be found in the Linux kernel source in the file
              Documentation/admin-guide/binfmt-misc.rst (or in Documentation/binfmt_misc.txt on older kernels).

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

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

              * nr_unused is the number of unused dentries.

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

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

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

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

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

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

       /proc/sys/fs/file-max
              This file defines a system-wide limit on the number of open files for all processes.  System calls
              that  fail when encountering this limit fail with the error ENFILE.  (See also setrlimit(2), which
              can be used by a process to set the per-process limit, RLIMIT_NOFILE, on the number  of  files  it
              may  open.)  If you get lots of error messages in the kernel log about running out of file handles
              (open file descriptions) (look for "VFS: file-max limit <number> reached"),  try  increasing  this
              value:

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

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

       /proc/sys/fs/file-nr
              This  (read-only)  file  contains  three  numbers: the number of allocated file handles (i.e., the
              number of open file descriptions; see open(2)); the number of free file handles; and  the  maximum
              number  of  file  handles  (i.e.,  the  same  value  as  /proc/sys/fs/file-max).  If the number of
              allocated file handles is close to the  maximum,  you  should  consider  increasing  the  maximum.
              Before  Linux  2.6,  the kernel allocated file handles dynamically, but it didn't free them again.
              Instead the free file handles were kept in a list for reallocation; the "free file handles"  value
              indicates  the  size of that list.  A large number of free file handles indicates that there was a
              past peak in the usage of open file handles.  Since Linux 2.6, the kernel  does  deallocate  freed
              file handles, and the "free file handles" value is always zero.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              0   Writing to FIFOs is unrestricted.

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

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

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

       /proc/sys/fs/protected_hardlinks (since Linux 3.6)
              When  the value in this file is 0, no restrictions are placed on the creation of hard links (i.e.,
              this is the historical behavior before Linux 3.6).  When the value in this file is 1, a hard  link
              can be created to a target file only if one of the following conditions is true:

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

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

              *  All of the following conditions are true:

                  •  the target is a regular file;

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

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

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

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

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

              0   Writing to regular files is unrestricted.

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

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

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

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

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

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

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

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

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

       /proc/sys/fs/suid_dumpable (since Linux 2.6.13)
              The value in this file is assigned to a process's "dumpable" flag in the  circumstances  described
              in  prctl(2).   In  effect, the value in this file determines whether core dump files are produced
              for set-user-ID or otherwise protected/tainted binaries.  The "dumpable" setting also affects  the
              ownership of files in a process's /proc/[pid] directory, as described above.

              Three different integer values can be specified:

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

              1 ("debug")
                     All processes dump core when possible.  (Reasons why a process might nevertheless not  dump
                     core  are  described  in core(5).)  The core dump is owned by the filesystem user ID of the
                     dumping process and no  security  is  applied.   This  is  intended  for  system  debugging
                     situations  only: this mode is insecure because it allows unprivileged users to examine the
                     memory contents of privileged processes.

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

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

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

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

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

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

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

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

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

       /proc/sys/kernel/cap_last_cap (since Linux 3.2)
              See capabilities(7).

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

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

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

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

       /proc/sys/kernel/ctrl-alt-del
              This file controls the handling of Ctrl-Alt-Del from the keyboard.  When the value in this file is
              0, Ctrl-Alt-Del is trapped and sent to the init(1) program to handle a graceful restart.  When the
              value  is  greater  than  zero, Linux's reaction to a Vulcan Nerve Pinch (tm) will be an immediate
              reboot, without even syncing its dirty buffers.  Note:  when  a  program  (like  dosemu)  has  the
              keyboard  in "raw" mode, the ctrl-alt-del is intercepted by the program before it ever reaches the
              kernel tty layer, and it's up to the program to decide what to do with it.

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

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

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

              has the same effect as

                  # hostname 'darkstar'
                  # domainname 'mydomain'

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

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

       /proc/sys/kernel/htab-reclaim (before Linux 2.4.9.2)
              (PowerPC only) If this file is set  to  a  nonzero  value,  the  PowerPC  htab  (see  kernel  file
              Documentation/powerpc/ppc_htab.txt) is pruned each time the system hits the idle loop.

       /proc/sys/kernel/keys/*
              This  directory  contains  various  files that define parameters and limits for the key-management
              facility.  These files are described in keyrings(7).

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

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

       /proc/sys/kernel/modprobe
              This   file   contains  the  pathname  for  the  kernel  module  loader.   The  default  value  is
              /sbin/modprobe.  The file is  present  only  if  the  kernel  is  built  with  the  CONFIG_MODULES
              (CONFIG_KMOD  in  Linux  2.6.26  and earlier) option enabled.  It is described by the Linux kernel
              source file Documentation/kmod.txt (present only in kernel 2.4 and earlier).

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

       /proc/sys/kernel/msgmax (since Linux 2.2)
              This  file  defines a system-wide limit specifying the maximum number of bytes in a single message
              written on a System V message queue.

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

       /proc/sys/kernel/msgmnb (since Linux 2.2)
              This  file  defines  a  system-wide  parameter  used  to  initialize  the  msg_qbytes  setting for
              subsequently created message queues.  The msg_qbytes setting specifies the maximum number of bytes
              that may be written to the message queue.

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

       /proc/sys/kernel/ns_last_pid (since Linux 3.3)
              See pid_namespaces(7).

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

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

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

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

       /proc/sys/kernel/pid_max (since Linux 2.5.34)
              This file specifies the value at which PIDs wrap around (i.e., the  value  in  this  file  is  one
              greater than the maximum PID).  PIDs greater than this value are not allocated; thus, the value in
              this file also acts as a system-wide limit on the total number  of  processes  and  threads.   The
              default  value  for this file, 32768, results in the same range of PIDs as on earlier kernels.  On
              32-bit platforms, 32768 is the maximum value for pid_max.  On 64-bit systems, pid_max can  be  set
              to any value up to 2^22 (PID_MAX_LIMIT, approximately 4 million).

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

       /proc/sys/kernel/printk
              See syslog(2).

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

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

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

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

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

       /proc/sys/kernel/randomize_va_space (since Linux 2.6.12)
              Select  the address space layout randomization (ASLR) policy for the system (on architectures that
              support ASLR).  Three values are supported for this file:

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

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

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

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

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

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

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

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

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

       /proc/sys/kernel/sched_rr_timeslice_ms (since Linux 3.9)
              See sched_rr_get_interval(2).

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

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

       /proc/sys/kernel/seccomp (since Linux 4.14)
              This directory provides additional seccomp information  and  configuration.   See  seccomp(2)  for
              further details.

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

              SEMMSL  The maximum semaphores per semaphore set.

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

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

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

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

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

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

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

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

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

       /proc/sys/kernel/shmmax (since Linux 2.2)
              This file can be used to query and set the run-time limit on the maximum  (System  V  IPC)  shared
              memory  segment  size that can be created.  Shared memory segments up to 1 GB are now supported in
              the kernel.  This value defaults to SHMMAX.

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

       /proc/sys/kernel/sysctl_writes_strict (since Linux 3.16)
              The  value in this file determines how the file offset affects the behavior of updating entries in
              files under /proc/sys.  The file has three possible values:

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

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

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

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

              0    Disable sysrq completely

              1    Enable all functions of sysrq

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

              This  file  is present only if the CONFIG_MAGIC_SYSRQ kernel configuration option is enabled.  For
              further  details  see  the  Linux  kernel  source  file  Documentation/admin-guide/sysrq.rst   (or
              Documentation/sysrq.txt before Linux 4.10).

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

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

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

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

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

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

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

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

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

       /proc/sys/net/core/bpf_jit_enable
              See bpf(2).

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

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

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

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

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

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

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

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

              Changing the value in this file takes effect whenever an application requests memory.

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

              Present only if the kernel was configured with CONFIG_COMPACTION.

       /proc/sys/vm/drop_caches (since Linux 2.6.16)
              Writing  to  this  file  causes the kernel to drop clean caches, dentries, and inodes from memory,
              causing that memory to become free.   This  can  be  useful  for  memory  management  testing  and
              performing  reproducible  filesystem benchmarks.  Because writing to this file causes the benefits
              of caching to be lost, it can degrade overall system performance.

              To free pagecache, use:

                  echo 1 > /proc/sys/vm/drop_caches

              To free dentries and inodes, use:

                  echo 2 > /proc/sys/vm/drop_caches

              To free pagecache, dentries and inodes, use:

                  echo 3 > /proc/sys/vm/drop_caches

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

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

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

              The file has one of the following values:

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

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

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

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

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

              Present only if the kernel was configured with CONFIG_MEMORY_FAILURE.

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

              1:  Attempt recovery.

              0:  Always panic on a memory failure.

              Present only if the kernel was configured with CONFIG_MEMORY_FAILURE.

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

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

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

              The default value is 0.

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

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

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

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

              The default value is 0.

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

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

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

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

              In  mode  0,  calls  of  mmap(2) with MAP_NORESERVE are not checked, and the default check is very
              weak, leading to the risk of getting a process "OOM-killed".

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

              In mode 2 (available since Linux 2.6), the total virtual  address  space  that  can  be  allocated
              (CommitLimit in /proc/meminfo) is calculated as

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

              where:

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

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

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

                   *  total_swap is the amount of swap space.

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

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

                  CommitLimit = overcommit_kbytes + total_swap

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

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

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

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

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

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

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

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

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

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

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

              Changing the value in this file takes effect whenever an application requests memory.

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

       /proc/sysrq-trigger (since Linux 2.4.21)
              Writing a character to this file triggers the same SysRq function as typing  ALT-SysRq-<character>
              (see  the  description  of  /proc/sys/kernel/sysrq).  This file is normally writable only by root.
              For further details see the  Linux  kernel  source  file  Documentation/admin-guide/sysrq.rst  (or
              Documentation/sysrq.txt before Linux 4.10).

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

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

       /proc/timer_list (since Linux 2.6.21)
              This read-only file exposes a list of all currently pending (high-resolution) timers,  all  clock-
              event sources, and their parameters in a human-readable form.

       /proc/timer_stats (from  Linux 2.6.21 until Linux 4.10)
              This  is  a debugging facility to make timer (ab)use in a Linux system visible to kernel and user-
              space developers.  It can be used by kernel and user-space developers to verify  that  their  code
              does  not  make undue use of timers.  The goal is to avoid unnecessary wakeups, thereby optimizing
              power consumption.

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

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

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

                  # echo 1 > /proc/timer_stats

              The following command stops a sampling period:

                  # echo 0 > /proc/timer_stats

              The statistics can be retrieved by:

                  $ cat /proc/timer_stats

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

              Sample output from /proc/timer_stats:

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

              The output columns are:

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

              *  the PID of the process that initialized the timer;

              *  the name of the process that initialized the timer;

              *  the function where the timer was initialized; and

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

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

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

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

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

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

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

              nr_free_pages (since Linux 2.6.31)

              nr_alloc_batch (since Linux 3.12)

              nr_inactive_anon (since Linux 2.6.28)

              nr_active_anon (since Linux 2.6.28)

              nr_inactive_file (since Linux 2.6.28)

              nr_active_file (since Linux 2.6.28)

              nr_unevictable (since Linux 2.6.28)

              nr_mlock (since Linux 2.6.28)

              nr_anon_pages (since Linux 2.6.18)

              nr_mapped (since Linux 2.6.0)

              nr_file_pages (since Linux 2.6.18)

              nr_dirty (since Linux 2.6.0)

              nr_writeback (since Linux 2.6.0)

              nr_slab_reclaimable (since Linux 2.6.19)

              nr_slab_unreclaimable (since Linux 2.6.19)

              nr_page_table_pages (since Linux 2.6.0)

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

              nr_unstable (since Linux 2.6.0)

              nr_bounce (since Linux 2.6.12)

              nr_vmscan_write (since Linux 2.6.19)

              nr_vmscan_immediate_reclaim (since Linux 3.2)

              nr_writeback_temp (since Linux 2.6.26)

              nr_isolated_anon (since Linux 2.6.32)

              nr_isolated_file (since Linux 2.6.32)

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

              nr_dirtied (since Linux 2.6.37)

              nr_written (since Linux 2.6.37)

              nr_pages_scanned (since Linux 3.17)

              numa_hit (since Linux 2.6.18)

              numa_miss (since Linux 2.6.18)

              numa_foreign (since Linux 2.6.18)

              numa_interleave (since Linux 2.6.18)

              numa_local (since Linux 2.6.18)

              numa_other (since Linux 2.6.18)

              workingset_refault (since Linux 3.15)

              workingset_activate (since Linux 3.15)

              workingset_nodereclaim (since Linux 3.15)

              nr_anon_transparent_hugepages (since Linux 2.6.38)

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

              nr_dirty_threshold (since Linux 2.6.37)

              nr_dirty_background_threshold (since Linux 2.6.37)

              pgpgin (since Linux 2.6.0)

              pgpgout (since Linux 2.6.0)

              pswpin (since Linux 2.6.0)

              pswpout (since Linux 2.6.0)

              pgalloc_dma (since Linux 2.6.5)

              pgalloc_dma32 (since Linux 2.6.16)

              pgalloc_normal (since Linux 2.6.5)

              pgalloc_high (since Linux 2.6.5)

              pgalloc_movable (since Linux 2.6.23)

              pgfree (since Linux 2.6.0)

              pgactivate (since Linux 2.6.0)

              pgdeactivate (since Linux 2.6.0)

              pgfault (since Linux 2.6.0)

              pgmajfault (since Linux 2.6.0)

              pgrefill_dma (since Linux 2.6.5)

              pgrefill_dma32 (since Linux 2.6.16)

              pgrefill_normal (since Linux 2.6.5)

              pgrefill_high (since Linux 2.6.5)

              pgrefill_movable (since Linux 2.6.23)

              pgsteal_kswapd_dma (since Linux 3.4)

              pgsteal_kswapd_dma32 (since Linux 3.4)

              pgsteal_kswapd_normal (since Linux 3.4)

              pgsteal_kswapd_high (since Linux 3.4)

              pgsteal_kswapd_movable (since Linux 3.4)

              pgsteal_direct_dma

              pgsteal_direct_dma32 (since Linux 3.4)

              pgsteal_direct_normal (since Linux 3.4)

              pgsteal_direct_high (since Linux 3.4)

              pgsteal_direct_movable (since Linux 2.6.23)

              pgscan_kswapd_dma

              pgscan_kswapd_dma32 (since Linux 2.6.16)

              pgscan_kswapd_normal (since Linux 2.6.5)

              pgscan_kswapd_high

              pgscan_kswapd_movable (since Linux 2.6.23)

              pgscan_direct_dma

              pgscan_direct_dma32 (since Linux 2.6.16)

              pgscan_direct_normal

              pgscan_direct_high

              pgscan_direct_movable (since Linux 2.6.23)

              pgscan_direct_throttle (since Linux 3.6)

              zone_reclaim_failed (since linux 2.6.31)

              pginodesteal (since linux 2.6.0)

              slabs_scanned (since linux 2.6.5)

              kswapd_inodesteal (since linux 2.6.0)

              kswapd_low_wmark_hit_quickly (since 2.6.33)

              kswapd_high_wmark_hit_quickly (since 2.6.33)

              pageoutrun (since Linux 2.6.0)

              allocstall (since Linux 2.6.0)

              pgrotated (since Linux 2.6.0)

              drop_pagecache (since Linux 3.15)

              drop_slab (since Linux 3.15)

              numa_pte_updates (since Linux 3.8)

              numa_huge_pte_updates (since Linux 3.13)

              numa_hint_faults (since Linux 3.8)

              numa_hint_faults_local (since Linux 3.8)

              numa_pages_migrated (since Linux 3.8)

              pgmigrate_success (since Linux 3.8)

              pgmigrate_fail (since Linux 3.8)

              compact_migrate_scanned (since Linux 3.8)

              compact_free_scanned (since Linux 3.8)

              compact_isolated (since Linux 3.8)

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

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

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

              htlb_buddy_alloc_success (since Linux 2.6.26)

              htlb_buddy_alloc_fail (since Linux 2.6.26)

              unevictable_pgs_culled (since Linux 2.6.28)

              unevictable_pgs_scanned (since Linux 2.6.28)

              unevictable_pgs_rescued (since Linux 2.6.28)

              unevictable_pgs_mlocked (since Linux 2.6.28)

              unevictable_pgs_munlocked (since Linux 2.6.28)

              unevictable_pgs_cleared (since Linux 2.6.28)

              unevictable_pgs_stranded (since Linux 2.6.28)

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

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

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

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

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

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

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

              balloon_inflate (since Linux 3.18)

              balloon_deflate (since Linux 3.18)

              balloon_migrate (since Linux 3.18)

              nr_tlb_remote_flush (since Linux 3.12)

              nr_tlb_remote_flush_received (since Linux 3.12)

              nr_tlb_local_flush_all (since Linux 3.12)

              nr_tlb_local_flush_one (since Linux 3.12)

              vmacache_find_calls (since Linux 3.16)

              vmacache_find_hits (since Linux 3.16)

              vmacache_full_flushes (since Linux 3.19)

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

NOTES

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

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

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

SEE ALSO

       cat(1),  dmesg(1),  find(1),  free(1),  htop(1),  init(1), ps(1), pstree(1), tr(1), uptime(1), chroot(2),
       mmap(2),  readlink(2),  syslog(2),  slabinfo(5),  sysfs(5),  hier(7),  namespaces(7),  time(7),   arp(8),
       hdparm(8), ifconfig(8), lsmod(8), lspci(8), mount(8), netstat(8), procinfo(8), route(8), sysctl(8)

       The   Linux   kernel   source   files:  Documentation/filesystems/proc.txt,  Documentation/sysctl/fs.txt,
       Documentation/sysctl/kernel.txt, Documentation/sysctl/net.txt, and Documentation/sysctl/vm.txt.

COLOPHON

       This page is part of release 5.10 of  the  Linux  man-pages  project.   A  description  of  the  project,
       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       https://www.kernel.org/doc/man-pages/.