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       /proc is a pseudo-filesystem which is used as an interface
       to kernel data structures rather than reading  and  inter­
       preting  /dev/kmem.   Most  of  it  is read-only, but some
       files allow kernel variables to be changed.

       The following outline gives a quick tour through the /proc

              There  is a numerical subdirectory for each running
              process; the subdirectory is named by  the  process
              ID.   Each  contains the following pseudo-files and

                     This holds the complete command line for the
                     process,  unless  the whole process has been
                     swapped out, or unless the process is a zom­
                     bie.   In either of these later cases, there
                     is nothing in this file: i.e. a read on this
                     file  will return 0 characters.  The command
                     line arguments appear in this file as a  set
                     of  null-separated  strings,  with a further
                     null byte after the last string.

              cwd    This is a link to the current working direc­
                     tory of the process.  To find out the cwd of
                     process 20, for instance, you can do this:

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

                     Note that the pwd command is often  a  shell
                     builtin,  and  might  not  work properly. In
                     bash, you may use pwd -P.

                     This file contains the environment  for  the
                     process.   The entries are separated by null
                     characters, and there may be a null  charac­
                     ter  at  the  end.   Thus,  to print out the
                     environment of process 1, you would do:

                     (cat /proc/1/environ; echo) | tr "\000" "\n"

                     (For a reason why  one  should  want  to  do
                     this, see lilo(8).)

              exe    Under  Linux  2.2  and 2.4 exe is a symbolic
                     link containing the actual path name of  the
                     For example, [0301]:1502 would be inode 1502
                     on device major 03 (IDE, MFM,  etc.  drives)
                     minor  01  (first  partition  on  the  first

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

              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 (as the exe
                     entry  does).   Thus, 0 is standard input, 1
                     standard output, 2 standard error, etc.

                     Programs that will take a filename, but will
                     not take the standard input, and which write
                     to a file, but will not send their output to
                     standard  output,  can be effectively foiled
                     this way, assuming that -i is the flag  des­
                     ignating  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.   Note  that
                     this will not work for programs that seek on
                     their files, as the files in the  fd  direc­
                     tory are not seekable.

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

              maps   A  file containing the currently mapped mem­
                     ory regions and their access permissions.

                     The format is:

        address           perms offset  dev   inode      pathname
        08048000-08056000 r-xp 00000000 03:0c 64593      /usr/sbin/gpm
        08056000-08058000 rw-p 0000d000 03:0c 64593      /usr/sbin/gpm
        08058000-0805b000 rwxp 00000000 00:00 0
        40000000-40013000 r-xp 00000000 03:0c 4165       /lib/ld-2.2.4.so
        40013000-40015000 rw-p 00012000 03:0c 4165       /lib/ld-2.2.4.so
        4001f000-40135000 r-xp 00000000 03:0c 45494      /lib/libc-2.2.4.so
        40135000-4013e000 rw-p 00115000 03:0c 45494      /lib/libc-2.2.4.so
        4013e000-40142000 rw-p 00000000 00:00 0
        bffff000-c0000000 rwxp 00000000 00:00 0

                     where address is the address  space  in  the
                     process  that it occupies, perms is a set of
                     Under Linux 2.0 there  is  no  field  giving

              mem    Via the mem file one can access the pages of
                     a process's memory through open(2), read(2),
                     and fseek(3).

              root   Unix  and  Linux  support the idea of a per-
                     process root of the filesystem, set  by  the
                     chroot(2)  system  call.  Root points to the
                     file system root, and behaves as exe,  fd/*,
                     etc. do.

              stat   Status  information about the process.  This
                     is  used  by  ps(1).   It  is   defined   in

                     The  fields,  in  order,  with  their proper
                     scanf(3) format specifiers, are:

                      pid %d The process id.

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

                     state %c
                             One   character   from   the  string
                             "RSDZTW" where R is  running,  S  is
                             sleeping in an interruptible wait, D
                             is waiting in  uninterruptible  disk
                             sleep,  Z  is zombie, T is traced or
                             stopped (on a signal), and W is pag­

                     ppid %d
                             The PID of the parent.

                     pgrp %d
                             The process group ID of the process.

                     session %d
                             The session ID of the process.

                     tty_nr %d
                             The tty the process uses.

                     tpgid %d
                             The process group ID of the  process
                             which  currently  owns  the tty that
                             The  number of minor faults that the
                             process and its children have  made.

                     majflt %lu
                             The  number of major faults the pro­
                             cess has made  which  have  required
                             loading a memory page from disk.

                     cmajflt %lu
                             The  number of major faults that the
                             process and its children have  made.

                     utime %lu
                             The number of jiffies that this pro­
                             cess  has  been  scheduled  in  user

                     stime %lu
                             The number of jiffies that this pro­
                             cess has been  scheduled  in  kernel

                     cutime %ld
                             The number of jiffies that this pro­
                             cess  and  its  children  have  been
                             scheduled in user mode.

                     cstime %ld
                             The number of jiffies that this pro­
                             cess  and  its  children  have  been
                             scheduled in kernel mode.

                     priority %ld
                             The  standard  nice value, plus fif­
                             teen.  The value is  never  negative
                             in the kernel.

                     nice %ld
                             The   nice   value  ranges  from  19
                             (nicest) to -19 (not  nice  to  oth­

                      0 %ld  This  value  is hard coded to 0 as a
                             placeholder for a removed field.

                     itrealvalue %ld
                             The time in jiffies before the  next
                             SIGALRM  is  sent to the process due
                             to an interval timer.

                     starttime %lu
                             The  time  in  jiffies  the  process

                     rlim %lu
                             Current limit in bytes on the rss of
                             the  process  (usually 4294967295 on

                     startcode %lu
                             The address above which program text
                             can run.

                     endcode %lu
                             The address below which program text
                             can run.

                     startstack %lu
                             The address  of  the  start  of  the

                     kstkesp %lu
                             The  current  value  of  esp  (stack
                             pointer), as  found  in  the  kernel
                             stack page for the process.

                     kstkeip %lu
                             The    current    EIP   (instruction

                     signal %lu
                             The bitmap of pending signals  (usu­
                             ally 0).

                     blocked %lu
                             The  bitmap of blocked signals (usu­
                             ally 0, 2 for shells).

                     sigignore %lu
                             The bitmap of ignored signals.

                     sigcatch %lu
                             The bitmap of catched signals.

                     wchan %lu
                             This is the "channel" in  which  the
                             process   is  waiting.   It  is  the
                             address of a system call, and can be
                             looked  up in a namelist if you need
                             a textual name.  (If you have an up-
                             to-date /etc/psdatabase, then try ps
                             -l  to  see  the  WCHAN   field   in

                     nswap %lu

              statm  Provides information about memory status  in
                     pages.  The columns are:
                      size       total program size
                      resident   resident set size
                      share      shared pages
                      trs        text (code)
                      drs        data/stack
                      lrs        library
                      dt         dirty pages

              status Provides much of the information in stat and
                     statm in an format that's easier for  humans
                     to parse.

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

       bus    Contains subdirectories for installed busses.

              pccard Subdirectory  for  pcmcia  devices when CON­
                     FIG_PCMCIA  is  set  at  kernel  compilation


              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.

                             Information about pci devices.  They
                             may be accessed through lspci(8) and

              Arguments  passed to the Linux kernel at boot time.
              Often done via a boot manager such as lilo(1).

              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 con­
              stant that is calculated during kernel  initializa­
              tion.   SMP machines have information for each CPU.

              Text listing of major numbers  and  device  groups.
              This can be used by MAKEDEV scripts for consistency
              with the kernel.
              piled into the kernel.  Incidentally, this is  used
              by  mount(1) to cycle through different filesystems
              when none is specified.

       fs     Empty subdirectory.

       ide    ide 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 hexidecimal
              media              media type
              model              manufacturer's model number
              settings           drive settings
              smart_thresholds   in hexidecimal
              smart_values       in hexidecimal

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

              This is used to record the number of interrupts per
              each IRQ on (at least) the i386 architechure.  Very
              easy to read formatting, done in ASCII.

       iomem  I/O memory map in Linux 2.4.

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

       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 struc­

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

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

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

       malloc This file is only present if CONFIGDEBUGMALLOC  was
              defined during compilation.

              This  is  used  by  free(1) to report the amount of
              free and used memory (both physical  and  swap)  on
              the system as well as the shared memory and buffers
              used by the kernel.

              It is in the same  format  as  free(1),  except  in
              bytes rather than KB.

       mounts This  is  a  list of all the file systems currently
              mounted on the system.  The format of this file  is
              documented in fstab(5).

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

       mtrr   Memory     Type     Range      Registers.       See
              /usr/src/linux/Documentation/mtrr.txt  for details.

       net    various net pseudo-files, all  of  which  give  the
              status of some part of the networking layer.  These
              files contain ASCII structures and are,  therefore,
              readable  with  cat.   However,  the  standard net­
              stat(8) suite provides much cleaner access to these

              arp    This  holds  an  ASCII  readable dump of the
                     kernel ARP table used  for  address  resolu­
                     tions. It will show both dynamically learned
                     and pre-programmed ARP entries.  The  format

        IP address     HW type   Flags     HW address          Mask   Device   0x1       0x2       00:50:BF:25:68:F3   *      eth0  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 inter­
              nal flags of  the  ARP  structure  (as  defined  in
              /usr/include/linux/if_arp.h)  and  the 'HW address'
              is the physical layer mapping for that  IP  address
              if it is known.

                     Defined                                   in
                          indx ifterface_name  dmi_u dmi_g dmi_address
                          2    eth0            1     0     01005e000001
                          3    eth1            1     0     01005e000001
                          4    eth2            1     0     01005e000001

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

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

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

              snmp   This  file  holds  the ASCII data needed for
                     the IP, ICMP, TCP, and UDP management infor­
                     mation bases for an snmp agent.

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

 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

              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

              Here 'Num' is the kernel table slot  number,  'Ref­
              Count'  is the number of users of the socket, 'Pro­
              tocol' is currently always 0, 'Flags' represent the
              internal  kernel  flags  holding  the status of the
              socket. Currently, type is always '1' (Unix  domain
              datagram  sockets are not yet supported in the ker­
              nel). 'St' is the internal state of the socket  and
              Path is the bound path (if any) of the socket.

              Contains  major and minor numbers of each partition
              as well as number of blocks and partition name.

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

       scsi   A  directory with the scsi midlevel pseudo-file and
              various SCSI  lowlevel  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.

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

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

                     An  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.
                     Reading these files will usually show driver
                     and host configuration, statistics etc.

                     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.

       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  pro­

              Information about kernel caches.  The columns are:
              See slabinfo(5) for details.

       stat   kernel/system  statistics.   Varies  with architec­
              ture.  Common entries include:

              cpu  3357 0 4313 1362393
                     The number of jiffies (1/100ths of a second)
                     that  the  system  spent  in user mode, user
                     mode with low priority (nice), system  mode,
                     and  the  idle task, respectively.  The last
                     value should be 100 times the  second  entry
                     in the uptime pseudo-file.

              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
                     The number of interrupts received  from  the
                     system boot.

              disk_io: (2,0):(31,30,5764,1,2) (3,0):...

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

       sys    This directory (present since  1.3.57)  contains  a
              number of files and subdirectories corresponding to
              kernel variables.  These variables can be read  and
              sometimes  modified using the proc file system, and
              the sysctl(2) system  call.  Presently,  there  are
              subdirectories  abi,  debug,  dev, fs, kernel, net,
              proc, rxrpc, sunrpc and vm that each  contain  more
              files and subdirectories.

              abi    This directory may contain files with appli­
                     cation binary information.  On some systems,
                     it is not present.

              debug  This directory may be empty.

              dev    This   directory  contains  device  specific
                     information (eg  dev/cdrom/info).   On  some
                     systems, it may be empty.

              fs     This  contains  the subdirectory binfmt_misc
                     and files  dentry-state,  dir-notify-enable,
                     dquot-nr,   file-max,   file-nr,  inode-max,
                     inode-nr,   inode-state,   lease-break-time,
                     leases-enable,    overflowgid,   overflowuid
                     super-max and super-nr with function  fairly
                     clear from the name.

              Documentation       for      the      files      in
              /proc/sys/binfmt_misc can be found  in  the  kernel
              sources in Documentation/binfmt_misc.txt.

              The file dentry-state contains six numbers, nr_den­
              try,  nr_unused,  age_limit   (age   in   seconds),
              want_pages  (pages  requested  by  system)  and two
              dummy values.  nr_dentry seems  to  be  0  all  the
              time.   nr_unused  seems to be the number of unused
              dentries.  age_limit is the age  in  seconds  after
              which  dcache  entries can be reclaimed when memory
              is short and want_pages is nonzero when the  kernel
              has  called  shrink_dcache_pages()  and  the dcache
              isn't pruned yet.

              The file dir-notify-enable 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.

              The file dquot-max  shows  the  maximum  number  of
              cached  disk quota entries.  On some (2.4) systems,
              messages about running out  of  file  handles,  try
              increasing this value:

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

              The  kernel constant NR_OPEN imposes an upper limit
              on the value that may be placed in file-max.

              If you  increase  file-max,  be  sure  to  increase
              inode-max  to  3-4 times the new value of file-max,
              or you will run out of inodes.

              The (read-only) file file-nr gives  the  number  of
              files presently opened.  It contains three numbers:
              The number of allocated file handles, the number of
              free  file  handles  and the maximum number of file
              handles.  The kernel allocates file handles dynami­
              cally, but it doesn't free them again.  If the num­
              ber of allocated files is close to the maximum, you
              should  consider  increasing the maximum.  When the
              number  of  free  file  handles  is  large,  you've
              encountered  a  peak  in your usage of file handles
              and you probably don't need to increase  the  maxi­

              The  file  inode-max contains the maximum number of
              in-memory inodes.  On some (2.4)  systems,  it  may
              not  be  present.  This  value  should be 3-4 times
              larger than the value  in  file-max,  since  stdin,
              stdout  and  network  sockets also need an inode to
              handle them. When you regularly run out of  inodes,
              you need to increase this value.

              The  file  inode-nr  contains  the first two values
              from inode-state.

              The  file  inode-state  contains   seven   numbers:
              nr_inodes, nr_free_inodes, preshrink and four dummy
              values.  nr_inodes is the number of inodes the sys­
              tem  has allocated.  This can be slightly more than
              inode-max because Linux allocates them one  pageful
              at a time.  nr_free_inodes represents the number of
              free  inodes.   preshrink  is  nonzero   when   the
              nr_inodes > inode-max and the system needs to prune
              the inode list instead of allocating more.

              The  file  lease-break-time  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
              value before being written to disk.

              The  file  super-max controls the maximum number of
              superblocks, and thus the maximum number of mounted
              filesystems  the  kernel can have. You only need to
              increase  super-max  if  you  need  to  mount  more
              filesystems  than  the  current  value in super-max
              allows you to.  The file super-nr contains the num­
              ber of filesystems currently mounted.

              kernel This directory contains files acct, cad_pid,
                     cap-bound,   core_pattern,    core_uses_pid,
                     ctrl-alt-del, dentry-state, domainname, hot­
                     plug, hostname, htab-reclaim (PowerPC only),
                     java-appletviewer  (binfmt_java,  obsolete),
                     java-interpreter  (binfmt_java,   obsolete),
                     l2cr   (PowerPC   only),  modprobe,  msgmax,
                     msgmnb,  msgmni,  osrelease,  ostype,  over­
                     flowgid,  overflowuid, panic, panic_on_oops,
                     pid_max,   powersave-nap   (PowerPC   only),
                     printk,  random,  real-root-dev,  reboot-cmd
                     (SPARC only), rtsig-max, rtsig-nr, sem,  sg-
                     big-buff,  shmall,  shmmax,  shmmni,  sysrq,
                     tainted, threads-max, version and zero-paged
                     (PowerPC  only)  with  function fairly clear
                     from the name.

              The file acct contains  three  numbers:  highwater,
              lowwater   and  frequency.   If  BSD-style  process
              accounting is  enabled  these  values  control  its
              behaviour.  If  free  space on filesystem where the
              log lives goes below  lowwater  percent  accounting
              suspends.  If  free space gets above highwater per­
              cent 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% of space
              is free; resume it if >= 4% of space is free;  con­
              sider  information about amount of free space valid
              for 30 seconds.

              The file cap-bound holds the value  of  the  kernel
              capability bounding set (expressed as a signed dec­
              imal number).  This set is ANDed against the  capa­
              bilities permitted to a process during exec.

              The  file  core_pattern (new in Linux 2.5) provides
              finer control over the form of a core filename than
              the  obsolete  core_uses_pid  file described below.
              The name for a core file is controlled by  defining
              a  template in core_pattern.  The template can con­
              tain % specifiers which are substituted by the fol­
              % followed by any character other than those listed
              above.  All other characters in the template become
              a  literal  part of the core filename.  The maximum
              size of the resulting core filename  is  64  bytes.
              The  default  value  in  this  file is "core".  For
              backward compatibility, if  core_pattern  does  not
              include  "%p"  and  core_uses_pid is non-zero, then
              .PID will be appended to the core filename.

              The file core_uses_pid can be used control the nam­
              ing of a core dump file on Linux 2.4.  If this file
              contains the value 0, then a core dump file is sim­
              ply  named  core.  If this file contains a non-zero
              value, then the core dump file includes the process
              ID in a name of the form core.PID.

              The  file  ctrl-alt-del  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 > 0, Linux's reaction to a Vulcan
              Nerve Pinch (tm) will be an immediate reboot, with­
              out  even  syncing its dirty buffers.  Note: when a
              program (like dosemu) has  the  keyboard  in  'raw'
              mode,  the  ctrl-alt-del is 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.

              The file hotplug contains the path for the  hotplug
              policy  agent.   The  default  value  in  this file

              The files domainname and hostname can  be  used  to
              set  the NIS/YP domainname and the hostname of your
              box in exactly the same way as the commands domain­
              name and hostname, i.e.:

              # 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  Ser­
              vice)  or  YP  (Yellow Pages) domainname. These two
              domain  names  are  in  general  different.  For  a
              The  file  msgmax is a system-wide limit specifying
              the maximum number of bytes  in  a  single  message
              written on a System V message queue.

              The  file  msgmni  defines the system-wide limit on
              the number of  message  queue  identifiers.   (This
              file is only present in Linux 2.4 onwards.)

              The  file  msgmnb is a system-wide paramter used to
              initialise the msg_qbytes setting  for  subsequenly
              created  message  queues.   The  msg_qbytes setting
              specifies the maximum number of bytes that  may  be
              written to the message queue.

              The  files  ostype and osrelease give substrings of

              The files overflowgid and overflowuid duplicate the
              files          /proc/sys/fs/overflowgid         and

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

              The file panic_on_oops (new in Linux 2.5)  controls
              the  kernel's  behaviour  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 pan­
              ics.  If the panic file is also non-zero  then  the
              machine will be rebooted.

              The  file  pid_max (new in Linux 2.5) specifies the
              value at which PIDs wrap around (i.e., the value in
              this  file  is  one  greater than the maximum PID).
              The default value for this file, 32768, results  in
              the  same range of PIDs as on earlier kernels.  The
              value in this file can be set to any  value  up  to
              2^22 (PID_MAX_LIMIT, approximately 4 million).

              The  file  powersave-nap  (PowerPC only) contains a
              flag.  If set, Linux-PPC will use the 'nap' mode of
              powersaving,  otherwise  the  'doze'  mode  will be

              The  four  values  in  the  file  printk  are  con­
              controlling  the operation of the file /dev/random.

              The file real-root-dev is documented in the  kernel
              source file Documentation/initrd.txt.

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

              The file rtsig-max can be used to tune the  maximum
              number  of POSIX realtime (queued) signals that can
              be outstanding in the system.

              The file rtsig-nr shows the number  POSIX  realtime
              signals currently queued.

              The  file sem (available in Linux 2.4 onwards) con­
              tains 4 numbers defining limits for  System  V  IPC
              semaphores.  These fields are, in order:

              SEMMSL  The maximum semaphores per semaphore set.

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

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

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

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

              The  file  shmall contains the system-wide limit on
              the total number of pages of System V  shared  mem­

              The  file  shmmax  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.

              The   file  shmmni  (available  in  Linux  2.4  and
              onwards) specifies the system-wide  maximum  number
              of System V shared memory segments that can be cre­

              The    net   This   directory  contains  networking

              proc   This directory may be empty.

              sunrpc This directory supports Sun remote procedure
                     call for network file system (NFS).  On some
                     systems, it is not present.

              vm     This directory  contains  files  for  memory
                     management  tuning, buffer and cache manage­

              Subdirectory containing the pseudo-files  msg,  sem
              and  shm.   These files list the System V Interpro­
              cess  Communication  (IPC)  objects  (respectively:
              message queues, semaphores, and shared memory) that
              currently exist on the  system,  providing  similar
              information  to  that available via ipcs(1).  These
              files have  headers  and  are  formatted  (one  IPC
              object  per  line)  for easy understanding.  ipc(5)
              provides  further  background  on  the  information
              shown by these files.

       tty    Subdirectory containing the psuedo-files and subdi­
              rectories for tty drivers and line disciplines.

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

              This string identifies the kernel version  that  is
              currently  running.   It  includes  the contents of
              /proc/sys/ostype,      /proc/sys/osrelease      and
              /proc/sys/version.  For example:
            Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994


       cat(1),   find(1),   free(1),   mount(1),   ps(1),  tr(1),
       uptime(1),  chroot(2),  mmap(2),  readlink(2),  syslog(2),
       slabinfo(5),  hier(7), arp(8), dmesg(8), hdparm(8), ifcon­
       fig(8),  lsmod(8),  lspci(8),   netstat(8),   procinfo(8),
       route(8) /usr/src/linux/Documentation/filesystems/proc.txt


       This roughly conforms to a Linux  2.4.17  kernel.   Please
       update this as necessary!

       closely based on kernel source documentation files written
       by Rik van Riel.

                            2003-05-27                    PROC(5)
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