PROC(5)



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

NAME
       proc - process information pseudo-filesystem

DESCRIPTION
       The  proc filesystem is a pseudo-filesystem which provides an interface
       to kernel data structures.  It is commonly mounted at /proc.   Most  of
       it is read-only, but some files allow kernel variables to be changed.

   Mount options
       The proc filesystem supports the following mount options:

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

              0   Everybody  may  access all /proc/[pid] directories.  This is
                  the traditional behavior, and  the  default  if  this  mount
                  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.

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

       /proc/[pid]
              There is a numerical subdirectory for each running process;  the
              subdirectory is named by the process ID.

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

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

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

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

       /proc/[pid]/attr
              The files in this directory provide an API for security modules.
              The  contents  of  this directory are files that can be read and
              written in  order  to  set  security-related  attributes.   This
              directory  was  added  to support SELinux, but the intention was
              that the API be general enough to support  other  security  mod-
              ules.   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  pol-
              icy,  although use of this operation is only suitable for appli-
              cations 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  multi-threaded
              process  to set their security context via this node as it would
              yield an  inconsistency  among  the  security  contexts  of  the
              threads  sharing  the  same  memory  space.  Since Linux 2.6.28,
              SELinux lifted this restriction and began supporting "set" oper-
              ations  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 sup-
              port "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  multi-
              ple file creation calls within a program unless it is explicitly
              reset.   In  SELinux,  a  process   can   set   only   its   own
              /proc/[pid]/attr/fscreate attribute.

       /proc/[pid]/attr/keycreate (since Linux 2.6.18)
              If  a process writes a security context into this file, all sub-
              sequently created keys (add_key(2)) will be  labeled  with  this
              context.   For  further  information, see the kernel source file
              Documentation/keys.txt.

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

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

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

       /proc/[pid]/auxv (since 2.6.0-test7)
              This  contains  the  contents of the ELF interpreter information
              passed to the process at exec time.  The format is one  unsigned
              long  ID  plus one unsigned long value for each entry.  The last
              entry contains two zeros.  See also getauxval(3).

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

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

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

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

              The following values may be written to the file:

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

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

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

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

              Further values can be written to affect different properties:

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

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

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

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

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

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

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

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

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

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

                  $ cd /proc/20/cwd; /bin/pwd

              Note that the pwd command is often a shell built-in,  and  might
              not work properly.  In bash(1), you may use pwd -P.

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

              Permission  to  dereference  or read (readlink(2)) this symbolic
              link    is    governed    by    a     ptrace     access     mode
              PTRACE_MODE_READ_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:

                  $ strings /proc/1/environ

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

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

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

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

              Permission  to  dereference  or read (readlink(2)) this symbolic
              link    is    governed    by    a     ptrace     access     mode
              PTRACE_MODE_READ_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 sym-
              bolic link with contents of the form

                  anon_inode:<file-type>

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

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

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

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

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

              and you have a working filter.

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

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

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

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

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

              For regular files and directories, we see something like:

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

              The fields are as follows:

              pos    This is a decimal number showing the file offset.

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

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

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

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

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

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

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

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

              Each of the lines  beginning  tfd  describes  one  of  the  file
              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 hexadec-
                     imal).

              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).

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

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

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

              The fields are as follows:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              This  directory  appears  only  if the CONFIG_CHECKPOINT_RESTORE
              kernel   configuration    option    is    enabled.     Privilege
              (CAP_SYS_ADMIN)  is required to view the contents of this direc-
              tory.

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

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

              The format of the file is:

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

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

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

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

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

              There are additional helpful pseudo-paths:

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

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

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

                   [heap] The process's heap.

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

              Under Linux 2.0, there is no field giving pathname.

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

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

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

              The file contains lines of the form:

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

              The  numbers  in  parentheses  are  labels  for the descriptions
              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
                   top of the mount tree).

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

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

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

              (6)  mount options: per-mount options.

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

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

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

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

              (11) super options: per-superblock options.

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

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

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

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

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

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

              The fields in each line are:

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

              (2)  The mount point within the filesystem tree.

              (3)  The filesystem type.

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

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

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

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

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

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

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

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

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

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

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

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

              * whether the process is privileged (-); and

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

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

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

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

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

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

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

              Consequently, it is very simple for user  space  to  define  the
              amount  of  memory  to  consider  for  each  task.   Setting  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.

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

                   63     If set, the page is present in RAM.

                   62     If set, the page is in swap space

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

                   60-56 (since Linux 3.11)
                          Zero

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

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

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

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

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

              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.  (Fur-
              ther attempts to write to the file fail with the EPERM error.)

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

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

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

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

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

              The  "KernelPageSize" line (available since Linux 2.6.29) is the
              page size used by the kernel to back the  virtual  memory  area.
              This  matches the size used by the MMU in the majority of cases.
              However, one counter-example occurs on PPC64 kernels  whereby  a
              kernel  using  64kB  as a base page size may still use 4kB pages
              for the  MMU  on  older  processors.   To  distinguish  the  two
              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))  associ-
              ated  with  the virtual memory area.  This entry is present only
              if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTEC-
              TION_KEYS configuration option.

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

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

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

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

       /proc/[pid]/stack (since Linux 2.6.29)
              This  file  provides  a  symbolic trace of the function calls in
              this process's kernel stack.  This file is provided only if  the
              kernel   was  built  with  the  CONFIG_STACKTRACE  configuration
              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  speci-
              fiers, are listed below.  Whether or not certain of these fields
              display valid information is governed by a  ptrace  access  mode
              PTRACE_MODE_READ_FSCREDS | PTRACE_MODE_NOAUDIT  check  (refer to
              ptrace(2)).  If the check denies access, then the field value is
              displayed  as  0.   The  affected  fields are indicated with the
              marking [PT].

              (1) pid  %d
                        The process ID.

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

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

                        R  Running

                        S  Sleeping in an interruptible wait

                        D  Waiting in uninterruptible disk sleep

                        Z  Zombie

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

                        t  Tracing stop (Linux 2.6.33 onward)

                        W  Paging (only before Linux 2.6.0)

                        X  Dead (from Linux 2.6.0 onward)

                        x  Dead (Linux 2.6.33 to 3.13 only)

                        K  Wakekill (Linux 2.6.33 to 3.13 only)

                        W  Waking (Linux 2.6.33 to 3.13 only)

                        P  Parked (Linux 3.9 to 3.13 only)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              (24) rss  %ld
                        Resident  Set Size: number of pages the process has in
                        real memory.  This  is  just  the  pages  which  count
                        toward  text,  data,  or  stack  space.  This does not
                        include pages which have not been demand-loaded in, or
                        which are swapped out.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              The fields are as follows:

              * Name: Command run by this process.

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

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

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

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

              * Pid: Thread ID (see gettid(2)).

              * PPid: PID of parent process.

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

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

              * FDSize: Number of file descriptor slots currently allocated.

              * Groups: Supplementary group list.

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

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

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

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

              * VmPeak: Peak virtual memory size.

              * VmSize: Virtual memory size.

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

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

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

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

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

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

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

              * VmData, VmStk, VmExe: Size of data, stack, and text segments.

              * VmLib: Shared library code size.

              * VmPTE: Page table entries size (since Linux 2.6.10).

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

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

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

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

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

              * SigPnd,  ShdPnd:  Number of signals pending for thread and for
                process as a whole (see pthreads(7) and signal(7)).

              * SigBlk,  SigIgn,  SigCgt:  Masks  indicating   signals   being
                blocked, ignored, and caught (see signal(7)).

              * CapInh,  CapPrm,  CapEff:  Masks  of  capabilities  enabled in
                inheritable, permitted,  and  effective  sets  (see  capabili-
                ties(7)).

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

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

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

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

              * Cpus_allowed: Mask of CPUs  on  which  this  process  may  run
                (since Linux 2.6.24, see cpuset(7)).

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

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

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

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

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

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

       /proc/[pid]/task (since Linux 2.6.0-test6)
              This is a directory that  contains  one  subdirectory  for  each
              thread  in  the  process.   The name of each subdirectory is the
              numerical thread ID  ([tid])  of  the  thread  (see  gettid(2)).
              Within  each  of  these  subdirectories, there is a set of files
              with the same names and contents as under the /proc/[pid] direc-
              tories.  For attributes that are shared by all threads, the con-
              tents for each of the files under the task/[tid]  subdirectories
              will  be  the  same  as  in the corresponding file in the parent
              /proc/[pid] directory (e.g., in a multithreaded process, all  of
              the  task/[tid]/cwd  files  will  have  the  same  value  as the
              /proc/[pid]/cwd file in the parent directory, since all  of  the
              threads in a process share a working directory).  For attributes
              that are distinct for each thread, the corresponding files under
              task/[tid]  may  have  different values (e.g., various fields in
              each of the task/[tid]/status files may be  different  for  each
              thread),  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 ter-
              minated (typically by calling pthread_exit(3)).

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

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

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

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

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

              The lines shown for each timer have the following meanings:

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

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

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

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

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

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

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

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

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

                  (2^order) * PAGE_SIZE

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

              For example on a x86_64 system:

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

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

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

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

       /proc/bus
              Contains subdirectories for installed busses.

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

       /proc/bus/pccard/drivers

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

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

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

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

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

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

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

       /proc/crypto
              A list of the ciphers provided by the kernel  crypto  API.   For
              details,  see  the  kernel Linux Kernel Crypto API documentation
              available under the kernel source  directory  Documentation/Doc-
              Book.   (That 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 filesys-
              tem is specified and it didn't manage to determine the  filesys-
              tem  type.   Then  filesystems  contained in this file are tried
              (excepted those that are marked with "nodev").

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

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

                  cache              buffer size in KB
                  capacity           number of sectors
                  driver             driver version
                  geometry           physical and logical geometry
                  identify           in hexadecimal
                  media              media type
                  model              manufacturer's model number
                  settings           drive settings
                  smart_thresholds   in hexadecimal
                  smart_values       in hexadecimal

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

       /proc/interrupts
              This is used to record the number of interrupts per CPU  per  IO
              device.   Since  Linux 2.6.24, for the i386 and x86_64 architec-
              tures, at least, this also includes interrupts internal  to  the
              system  (that is, not associated with a device as such), such as
              NMI (nonmaskable interrupt), LOC (local  timer  interrupt),  and
              for  SMP  systems,  TLB (TLB flush interrupt), RES (rescheduling
              interrupt), CAL (remote function call interrupt),  and  possibly
              others.  Very easy to read formatting, done in ASCII.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       /proc/locks
              This  file  shows current file locks (flock(2) and fcntl(2)) and
              leases (fcntl(2)).  The lslocks(8) command provides a  bit  more
              information about each lock.

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

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

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

              MemFree %lu
                     The sum of LowFree+HighFree.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              SwapTotal %lu
                     Total amount of swap space available.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              VmallocTotal %lu
                     Total size of vmalloc memory area.

              VmallocUsed %lu
                     Amount of vmalloc area which is used.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              DirectMap1G %lu (since Linux 2.6.27)
                     (x86  with  CONFIG_X86_64  and  CONFIG_X86_DIRECT_GBPAGES
                     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  filesys-
              tems  currently mounted on the system.  With the introduction of
              per-process mount namespaces in Linux 2.4.19  (see  mount_names-
              paces(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/mtrr.txt for details.

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

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

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

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

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

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

       /proc/net/unix
              Lists the UNIX domain sockets  present  within  the  system  and
              their status.  The format is:
              Num RefCount Protocol Flags    Type St Path
               0: 00000002 00000000 00000000 0001 03
               1: 00000001 00000000 00010000 0001 01 /dev/printer

              The fields are as follows:

              Num:      the kernel table slot number.

              RefCount: the number of users of the socket.

              Protocol: currently always 0.

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

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

              St:       the internal state of the socket.

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

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

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

              The fields in each line are:

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

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

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

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

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

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

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

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

              The last number exists only for  compatibility  reasons  and  is
              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  ini-
              tialization and their configuration.

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

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

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

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

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

              The command

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

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

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

              Reading these files will usually show driver and host configura-
              tion, statistics, and so on.

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

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

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

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

              cpu  3357 0 4313 1362393
                     The   amount  of  time,  measured  in  units  of  USER_HZ
                     (1/100ths  of  a  second  on  most   architectures,   use
                     sysconf(_SC_CLK_TCK) to obtain the right value), that the
                     system spent in various states:

                     user   (1) Time spent in user mode.

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

                     system (3) Time spent in system mode.

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

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

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

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

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

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

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

                            steal (since Linux 2.6.11)
                               (8)  Stolen  time,  which  is the time spent in
                               other operating systems when running in a  vir-
                               tualized 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  con-
                               trol 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 architec-
                            ture  specific  interrupts; each subsequent column
                            is the total for that particular  numbered  inter-
                            rupt.   Unnumbered  interrupts are not shown, only
                            summed into the total.

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

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

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

                     processes 86031
                            Number of forks since boot.

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

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

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

              /proc/sys
                     This  directory  (present since 1.3.57) contains a number
                     of files and subdirectories corresponding to kernel vari-
                     ables.   These  variables can be read and sometimes modi-
                     fied 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 EIN-
                     VAL.

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

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

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

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

              /proc/sys/fs/binfmt_misc
                     Documentation for files in this directory can be found in
                     the    Linux     kernel     sources     in     Documenta-
                     tion/binfmt_misc.txt.

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

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

              /proc/sys/fs/inode-max (only present until Linux 2.2)
                     This  file  contains  the  maximum  number  of  in-memory
                     inodes.   This  value should be 3-4 times larger than the
                     value in file-max, since stdin, stdout and network  sock-
                     ets  also  need  an inode to handle them.  When you regu-
                     larly 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 allo-
                     cated.  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 allo-
                     cating 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 mes-
                     sage queues.  See mq_overview(7) for details.

              /proc/sys/fs/nr_open (since Linux 2.6.25)
                     This file imposes ceiling  on  the  value  to  which  the
                     RLIMIT_NOFILE  resource  limit  can  be raised (see getr-
                     limit(2)).  This ceiling is enforced  for  both  unprivi-
                     leged  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_hardlinks (since Linux 3.6)
                     When  the  value  in  this file is 0, no restrictions are
                     placed on the creation of hard links (i.e., this  is  the
                     historical behavior before Linux 3.6).  When the value in
                     this file is 1, a hard link can be created  to  a  target
                     file only if one of the following conditions is true:

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

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

                     *  All of the following conditions are true:

                         o  the target is a regular file;

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

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

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

                     The default value in this file is 0.  Setting  the  value
                     to  1  prevents  a  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  cre-
                     ated  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_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 EAC-
                     CES 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  sym-
                     bolic 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 sys-
                            tem  debugging situations only: this mode is inse-
                            cure because it allows unprivileged users to exam-
                            ine 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 admin-
                            istrators  are  attempting  to debug problems in a
                            normal environment.

                            Additionally,  since  Linux  3.6,   /proc/sys/ker-
                            nel/core_pattern  must either be an absolute path-
                            name 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" set-
                     ting 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 ker-
                     nel 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 lowwa-
                     ter 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  sec-
                     onds.

              /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 recomputa-
                     tion of msgmni based on the current amount  of  available
                     memory  and  number of IPC namespaces).  Echoing "0" dis-
                     abled 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 possi-
                     ble),  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 bound-
                     ing 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 sys-
                     tem-wide capability bounding  set  disappeared,  and  was
                     replaced  by  a  per-thread  bounding  set; see capabili-
                     ties(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 pro-
                     gram 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 sys-
                     log 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 dif-
                     ferent.  For a detailed discussion  see  the  hostname(1)
                     man page.

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

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

              /proc/sys/kernel/keys/*
                     This directory contains various files that define parame-
                     ters 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  inter-
                     faces.   A  value  of  0 in this file imposes no restric-
                     tions.  If the value is 1, kernel pointers printed  using
                     the  %pK  format  specifier  will  be replaced with zeros
                     unless the user has the CAP_SYSLOG  capability.   If  the
                     value  is 2, kernel pointers printed using the %pK format
                     specifier will be replaced with zeros regardless  of  the
                     user's  capabilities.  The initial default value for this
                     file was 1, but the default was changed  to  0  in  Linux
                     2.6.39.    Since   Linux   3.4,   only   users  with  the
                     CAP_SYS_ADMIN capability can change  the  value  in  this
                     file.

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

              /proc/sys/kernel/modprobe
                     This file contains the path for the kernel module loader.
                     The default value is /sbin/modprobe.  The file is present
                     only if the kernel is built with the CONFIG_MODULES (CON-
                     FIG_KMOD in Linux 2.6.26 and earlier) option enabled.  It
                     is  described  by the Linux kernel source file Documenta-
                     tion/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 tog-
                     gle 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 max-
                     imum  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/ker-
                     nel/auto_msgmni.

              /proc/sys/kernel/msgmnb (since Linux 2.2)
                     This file defines a system-wide parameter  used  to  ini-
                     tialize  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 mes-
                     sage queue.

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

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

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

              /proc/sys/kernel/panic
                     This file gives read/write access to the kernel  variable
                     panic_timeout.   If this is zero, the kernel will loop on
                     a panic; if nonzero, it indicates that the kernel  should
                     autoreboot  after  this  number of seconds.  When you use
                     the software watchdog device driver, the recommended set-
                     ting 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 allo-
                     cated; thus, the value in this file also acts as  a  sys-
                     tem-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) pol-
                     icy  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 con-
                        figured with CONFIG_COMPAT_BRK.

              /proc/sys/kernel/real-root-dev
                     This file is documented in the Linux kernel  source  file
                     Documentation/initrd.txt.

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

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

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

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

              /proc/sys/kernel/sched_child_runs_first (since Linux 2.6.23)
                     If this file contains  the  value  zero,  then,  after  a
                     fork(2),  the  parent  is first scheduled on the CPU.  If
                     the file contains a nonzero  value,  then  the  child  is
                     scheduled  first  on the CPU.  (Of course, on a multipro-
                     cessor system, the parent and the child might both  imme-
                     diately 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/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 sem-
                             aphore 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 seg-
                     ments will be marked for destruction as soon as the  num-
                     ber  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.  Set-
                     ting 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  descrip-
                     tion  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  1GB
                     are  now supported in the kernel.  This value defaults to
                     SHMMAX.

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

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

                     -1  This  provides  legacy handling, with no printk warn-
                         ings.  Each write(2) must fully contain the value  to
                         be  written,  and  multiple  writes  on the same file
                         descriptor will overwrite the entire  value,  regard-
                         less 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  ker-
                     nel configuration option is enabled.  For further details
                     see the Linux kernel source file Documentation/sysrq.txt.

              /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 argu-
                     ment 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 tun-
                     ing, 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  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 over-
                     commit 'guess' mode  (i.e.,  0  in  /proc/sys/vm/overcom-
                     mit_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 CON-
                     FIG_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 ben-
                     efits  of caching to be lost, it can degrade overall sys-
                     tem 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  opera-
                     tion  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  back-
                     ground  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 opera-
                     tion.

                     Present only if  the  kernel  was  configured  with  CON-
                     FIG_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  CON-
                     FIG_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, resi-
                     dent 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 iden-
                     tify the rogue task that caused it.

                     If this contains the value zero, this information is sup-
                     pressed.   On very large systems with thousands of tasks,
                     it may not be feasible to dump the memory state  informa-
                     tion  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 prece-
                     dence    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  Com-
                     mitLimit   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 sys-
                     tems 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 over-
                     commit_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  sys-
                             tem;

                          *  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 16GB of physical RAM, 16GB
                     of swap, no space dedicated to huge pages, and  an  over-
                     commit_ratio  of 50, this formula yields a CommitLimit of
                     24GB.

                     Since Linux 3.14, if the value  in  /proc/sys/vm/overcom-
                     mit_kbytes is nonzero, then CommitLimit is instead calcu-
                     lated as:

                         CommitLimit = overcommit_kbytes + total_swap

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

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

              /proc/sys/vm/panic_on_oom (since Linux 2.6.18)
                     This enables or disables a kernel panic in an out-of-mem-
                     ory 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 nor-
                     mally 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-mem-
                     ory 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 ker-
                     nel  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: Can-
                     not allocate memory".

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

              /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/sysrq.txt.

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

              /proc/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 pend-
                     ing  (high-resolution)  timers,  all clock-event sources,
                     and their parameters in a human-readable form.

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

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

                     The  /proc/timer_stats  file is used both to control sam-
                     pling 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 com-
                     mand:

                         # 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 associ-
                        ated with the timer.

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

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

              /proc/version
                     This string identifies the kernel version  that  is  cur-
                     rently    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 files 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 ker-
                     nel source code.)  The following fields may be present:

                     nr_free_pages (since Linux 2.6.31)

                     nr_alloc_batch (since Linux 3.12)

                     nr_inactive_anon (since Linux 2.6.28)

                     nr_active_anon (since Linux 2.6.28)

                     nr_inactive_file (since Linux 2.6.28)

                     nr_active_file (since Linux 2.6.28)

                     nr_unevictable (since Linux 2.6.28)

                     nr_mlock (since Linux 2.6.28)

                     nr_anon_pages (since Linux 2.6.18)

                     nr_mapped (since Linux 2.6.0)

                     nr_file_pages (since Linux 2.6.18)

                     nr_dirty (since Linux 2.6.0)

                     nr_writeback (since Linux 2.6.0)

                     nr_slab_reclaimable (since Linux 2.6.19)

                     nr_slab_unreclaimable (since Linux 2.6.19)

                     nr_page_table_pages (since Linux 2.6.0)

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

                     nr_unstable (since Linux 2.6.0)

                     nr_bounce (since Linux 2.6.12)

                     nr_vmscan_write (since Linux 2.6.19)

                     nr_vmscan_immediate_reclaim (since Linux 3.2)

                     nr_writeback_temp (since Linux 2.6.26)

                     nr_isolated_anon (since Linux 2.6.32)

                     nr_isolated_file (since Linux 2.6.32)

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

                     nr_dirtied (since Linux 2.6.37)

                     nr_written (since Linux 2.6.37)

                     nr_pages_scanned (since Linux 3.17)

                     numa_hit (since Linux 2.6.18)

                     numa_miss (since Linux 2.6.18)

                     numa_foreign (since Linux 2.6.18)

                     numa_interleave (since Linux 2.6.18)

                     numa_local (since Linux 2.6.18)

                     numa_other (since Linux 2.6.18)

                     workingset_refault (since Linux 3.15)

                     workingset_activate (since Linux 3.15)

                     workingset_nodereclaim (since Linux 3.15)

                     nr_anon_transparent_hugepages (since Linux 2.6.38)

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

                     nr_dirty_threshold (since Linux 2.6.37)

                     nr_dirty_background_threshold (since Linux 2.6.37)

                     pgpgin (since Linux 2.6.0)

                     pgpgout (since Linux 2.6.0)

                     pswpin (since Linux 2.6.0)

                     pswpout (since Linux 2.6.0)

                     pgalloc_dma (since Linux 2.6.5)

                     pgalloc_dma32 (since Linux 2.6.16)

                     pgalloc_normal (since Linux 2.6.5)

                     pgalloc_high (since Linux 2.6.5)

                     pgalloc_movable (since Linux 2.6.23)

                     pgfree (since Linux 2.6.0)

                     pgactivate (since Linux 2.6.0)

                     pgdeactivate (since Linux 2.6.0)

                     pgfault (since Linux 2.6.0)

                     pgmajfault (since Linux 2.6.0)

                     pgrefill_dma (since Linux 2.6.5)

                     pgrefill_dma32 (since Linux 2.6.16)

                     pgrefill_normal (since Linux 2.6.5)

                     pgrefill_high (since Linux 2.6.5)

                     pgrefill_movable (since Linux 2.6.23)

                     pgsteal_kswapd_dma (since Linux 3.4)

                     pgsteal_kswapd_dma32 (since Linux 3.4)

                     pgsteal_kswapd_normal (since Linux 3.4)

                     pgsteal_kswapd_high (since Linux 3.4)

                     pgsteal_kswapd_movable (since Linux 3.4)

                     pgsteal_direct_dma

                     pgsteal_direct_dma32 (since Linux 3.4)

                     pgsteal_direct_normal (since Linux 3.4)

                     pgsteal_direct_high (since Linux 3.4)

                     pgsteal_direct_movable (since Linux 2.6.23)

                     pgscan_kswapd_dma

                     pgscan_kswapd_dma32 (since Linux 2.6.16)

                     pgscan_kswapd_normal (since Linux 2.6.5)

                     pgscan_kswapd_high

                     pgscan_kswapd_movable (since Linux 2.6.23)

                     pgscan_direct_dma

                     pgscan_direct_dma32 (since Linux 2.6.16)

                     pgscan_direct_normal

                     pgscan_direct_high

                     pgscan_direct_movable (since Linux 2.6.23)

                     pgscan_direct_throttle (since Linux 3.6)

                     zone_reclaim_failed (since linux 2.6.31)

                     pginodesteal (since linux 2.6.0)

                     slabs_scanned (since linux 2.6.5)

                     kswapd_inodesteal (since linux 2.6.0)

                     kswapd_low_wmark_hit_quickly (since 2.6.33)

                     kswapd_high_wmark_hit_quickly (since 2.6.33)

                     pageoutrun (since Linux 2.6.0)

                     allocstall (since Linux 2.6.0)

                     pgrotated (since Linux 2.6.0)

                     drop_pagecache (since Linux 3.15)

                     drop_slab (since Linux 3.15)

                     numa_pte_updates (since Linux 3.8)

                     numa_huge_pte_updates (since Linux 3.13)

                     numa_hint_faults (since Linux 3.8)

                     numa_hint_faults_local (since Linux 3.8)

                     numa_pages_migrated (since Linux 3.8)

                     pgmigrate_success (since Linux 3.8)

                     pgmigrate_fail (since Linux 3.8)

                     compact_migrate_scanned (since Linux 3.8)

                     compact_free_scanned (since Linux 3.8)

                     compact_isolated (since Linux 3.8)

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

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

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

                     htlb_buddy_alloc_success (since Linux 2.6.26)

                     htlb_buddy_alloc_fail (since Linux 2.6.26)

                     unevictable_pgs_culled (since Linux 2.6.28)

                     unevictable_pgs_scanned (since Linux 2.6.28)

                     unevictable_pgs_rescued (since Linux 2.6.28)

                     unevictable_pgs_mlocked (since Linux 2.6.28)

                     unevictable_pgs_munlocked (since Linux 2.6.28)

                     unevictable_pgs_cleared (since Linux 2.6.28)

                     unevictable_pgs_stranded (since Linux 2.6.28)

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

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

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

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

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

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

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

                     balloon_inflate (since Linux 3.18)

                     balloon_deflate (since Linux 3.18)

                     balloon_migrate (since Linux 3.18)

                     nr_tlb_remote_flush (since Linux 3.12)

                     nr_tlb_remote_flush_received (since Linux 3.12)

                     nr_tlb_local_flush_all (since Linux 3.12)

                     nr_tlb_local_flush_one (since Linux 3.12)

                     vmacache_find_calls (since Linux 3.16)

                     vmacache_find_hits (since Linux 3.16)

                     vmacache_full_flushes (since Linux 3.19)

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

NOTES
       Many strings (i.e., the environment and command line) are in the inter-
       nal  format, with subfields terminated by null bytes ('\0'), so you may
       find that things are more readable if you use od -c or tr  "\000"  "\n"
       to read them.  Alternatively, echo `cat <file>` works well.

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

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

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

COLOPHON
       This  page  is  part of release 4.12 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

Linux                             2017-05-03                           PROC(5)

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