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       proc - process information pseudo-filesystem


       The  proc  filesystem  is  a  pseudo-filesystem  which  is  used  as 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

       The following outline gives a quick tour through the /proc hierarchy.

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

       /proc/[number]/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.

              This holds the complete command line for the process, unless the
              whole process has been swapped out or the process is  a  zombie.
              In  either of these latter cases, 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 null-
              separated strings, with a  further  null  byte  after  the  last

              This  is a symbolic link to the current working directory 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.

              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).

              This file contains the environment for the process.  The entries
              are  separated  by  null  bytes  (’\0’), and there may be a null
              bytes 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) or

              Under Linux  2.2  and  later,  this  file  is  a  symbolic  link
              containing  the  actual  pathname of the executed command.  This
              symbolic link can be dereferenced normally; attempting  to  open
              it    will   open   the   executable.    You   can   even   type
              /proc/[number]/exe to run another copy of the same executable as
              is  being  run by process [number].  In a multithreaded process,
              the contents of this symbolic link are not available if the main
              thread    has   already   terminated   (typically   by   calling

              Under Linux 2.0 and earlier /proc/[number]/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:


              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.

              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, etc.

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

              Programs that 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 designating an input file and
              -o is the flag designating an output file:

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

              and you have a working filter.

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

              A file containing the currently mapped memory 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/
        40013000-40015000 rw-p 00012000 03:0c 4165       /lib/
        4001f000-40135000 r-xp 00000000 03:0c 45494      /lib/
        40135000-4013e000 rw-p 00115000 03:0c 45494      /lib/
        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 permissions:

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

              offset is the offset into the file/whatever, dev is  the  device
              (major:minor),  and  inode  is  the  inode  on  that  device.  0
              indicates that no inode is associated with the memory region, as
              the case would be with bss.

              Under Linux 2.0 there is no field giving pathname.

              This  file can be used to access the pages of a process’s memory
              through open(2), read(2), and lseek(2).

              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 as exe, fd/*, etc. do.

              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)).

       /proc/[number]/smaps (since Linux 2.6.14)
              This  file  shows  memory  consumption for each of the process’s
              mappings.  For each of mappings there is a series  of  lines  as

                  08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
                  Size:               464 kB
                  Rss:                424 kB
                  Shared_Clean:       424 kB
                  Shared_Dirty:         0 kB
                  Private_Clean:        0 kB
                  Private_Dirty:        0 kB

              The  first  of  these  lines  shows  the  same information as is
              displayed for the mapping in /proc/[number]/maps.  The remaining
              lines  show  the  size of the mapping, the amount of the mapping
              that is currently resident in RAM, the number  clean  and  dirty
              shared  pages  in  the  mapping,  and the number clean and dirty
              private pages in the mapping.

              This file is only present if the CONFIG_MMU kernel configuration
              option is enabled.

              Status  information  about  the process.  This is used by ps(1).
              It is defined in /usr/src/linux/fs/proc/array.c.

              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 paging.

              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 process is connected to.

              flags %u (%lu before Linux 2.6.22)
                     The kernel flags word of the process.  For bit  meanings,
                     see  the PF_* defines in <linux/sched.h>.  Details depend
                     on the kernel version.

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

              cminflt %lu
                     The  number of minor faults that the process’s waited-for
                     children have made.

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

              cmajflt %lu
                     The  number of major faults that the process’s waited-for
                     children have made.

              utime %lu
                     The  number  of  jiffies  that  this  process  has   been
                     scheduled in user mode.

              stime %lu
                     The   number  of  jiffies  that  this  process  has  been
                     scheduled in kernel mode.

              cutime %ld
                     The number of  jiffies  that  this  process’s  waited-for
                     children  have  been  scheduled  in user mode.  (See also

              cstime %ld
                     The number of  jiffies  that  this  process’s  waited-for
                     children have been scheduled in kernel mode.

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

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

              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.

              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.

              starttime %llu (was %lu before Linux 2.6)
                     The time in jiffies  the  process  started  after  system

              vsize %lu
                     Virtual memory size in bytes.

              rss %ld
                     Resident  Set  Size:  number  of pages the process has in
                     real memory, minus 3 for administrative  purposes.   This
                     is  just  the  pages  which  count towards text, data, or
                     stack space.  This does not include pages which have  not
                     been demand-loaded in, or which are swapped out.

              rlim %lu
                     Current limit in bytes on the rss of the process (usually
                     4294967295 on i386).

              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 stack.

              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 pointer).

              signal %lu
                     The bitmap of pending signals.

              blocked %lu
                     The bitmap of blocked signals.

              sigignore %lu
                     The bitmap of ignored signals.

              sigcatch %lu
                     The bitmap of caught 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 action.)

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

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

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

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

              rt_priority %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
                     Real-time         scheduling         priority        (see

              policy %u (since Linux 2.5.19; was %lu before Linux 2.6.22)
                     Scheduling policy (see sched_setscheduler(2)).

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

              Provides  information about memory status in pages.  The columns

                  size       total program size
                  resident   resident set size
                  share      shared pages
                  text       text (code)
                  lib        library
                  data       data/stack
                  dt         dirty pages (unused in Linux 2.6)

              Provides much of  the  information  in  /proc/[number]/stat  and
              /proc/[number]/statm  in  a  format  that’s easier for humans to

       /proc/[number]/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 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/[number] directories.  For
              attributes that are shared by all threads, the contents for each
              of the files under the task/[thread-ID] subdirectories  will  be
              the   same   as   in   the  corresponding  file  in  the  parent
              /proc/[number] directory (e.g., in a multithreaded process,  all
              of  the  task/[thread-ID]/cwd  files will have the same value as
              the /proc/[number]/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/[thread-ID]  may have different values (e.g.,
              various fields in each of the task/[thread-ID]/status files  may
              be different for each thread).

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

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

              Contains subdirectories for installed busses.

              Subdirectory  for  pcmcia  devices  when CONFIG_PCMCIA is set at
              kernel compilation time.


              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 setpci(8).

              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  constant  that is calculated during kernel
              initialization.  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.

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

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

              Empty subdirectory.

              List of the execution domains (ABI personalities).

              Frame buffer information when CONFIG_FB is defined during kernel

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

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

              Empty subdirectory.

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

                  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.

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

              I/O memory map in Linux 2.4.

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

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

              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.

              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

              Information in this file is retrieved with the dmesg(8) program.

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

              The  first  three  fields  in this file are load average figures
              giving the number of jobs in the run queue (state R) or  waiting
              for disk I/O (state D) averaged over 1, 5, and 15 minutes.  They
              are the same as the load average numbers given by uptime(1)  and
              other  programs.   The  fourth  field  consists  of  two numbers
              separated by a slash (/).  The first of these is the  number  of
              currently   executing  kernel  scheduling  entities  (processes,
              threads); this will be less than or equal to the number of CPUs.
              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

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

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

              This is a list of all the file systems currently mounted on  the
              system.   The  format  of  this  file is documented in fstab(5).
              Since kernel  version  2.6.15,  this  file  is  pollable:  after
              opening  the  file  for  reading, a change in this file (i.e., a
              file system mount or unmount) causes select(2) to mark the  file
              descriptor  as  readable, and poll(2) and epoll_wait(2) mark the
              file as having an error condition.

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

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

              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  netstat(8) suite provides much cleaner access to these

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

        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 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.

              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

              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

              Internet    Group    Management    Protocol.      Defined     in

              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.

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

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

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

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

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

              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, ’RefCount’ is the
              number of users of the socket, ’Protocol’ 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 kernel). ’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.

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

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

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

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

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

              An echoscsi 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.

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

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

              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.

              Information about kernel caches.  Since Linux 2.6.16  this  file
              is  only  present if the CONFIG_SLAB kernel configuration option
              is enabled.  The columns in /proc/slabinfo are:


              See slabinfo(5) for details.

              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),  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 USER_HZ times the second entry
                     in the uptime pseudo-file.

                     In Linux 2.6 this line includes three additional columns:
                     iowait - time waiting for I/O to complete (since 2.5.41);
                     irq -  time  servicing  interrupts  (since  2.6.0-test4);
                     softirq - time servicing softirqs (since 2.6.0-test4).

                     Since  Linux  2.6.11,  there is an eighth column, steal -
                     stolen time, which is the time spent in  other  operating
                     systems when running in a virtualized environment

              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

              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;
                     each subsequent column is  the  total  for  a  particular

              disk_io: (2,0):(31,30,5764,1,2) (3,0):...
                     (major,minor):(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 (January 1, 1970).

              processes 86031
                     Number of forks since boot.

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

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

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

              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.

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

              This directory may be empty.

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

              This  contains  the  subdirectories  binfmt_misc,  inotify,  and
              mqueue,  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,
              suid_dumpable, super-max, and super-nr.

              Documentation for files in this directory can be  found  in  the
              kernel sources in Documentation/binfmt_misc.txt.

              This  file contains six numbers, nr_dentry, nr_unused, age_limit
              (age in seconds), want_pages (pages requested by system) and two
              dummy  values.  nr_dentry 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.

              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.

              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

              This  file  shows the number of allocated disk quota entries and
              the number of free disk quota entries.

              This file defines a system-wide limit  on  the  number  of  open
              files  for  all processes.  (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 about running out of file handles, try increasing  this

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

              This (read-only)  file  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 dynamically,
              but it doesn’t free them again.   If  the  number  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 maximum.

              This file 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.

              This file contains the first two values from inode-state.

              This file contains  seven  numbers:  nr_inodes,  nr_free_inodes,
              preshrink  and  four  dummy  values.  nr_inodes is the number of
              inodes the system has allocated.  This can be slightly more than
              inode-max  because Linux allocates them one page full 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.

       /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).

              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.

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

       /proc/sys/fs/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 only support
              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/suid_dumpable (since Linux 2.6.13)
              The  value  in  this file determines whether core dump files are
              produced  for   set-user-ID   or   otherwise   protected/tainted
              binaries.  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.  The core
              dump is owned by the file system user ID of the dumping  process
              and  no  security  is  applied.   This  is  intended  for system
              debugging situations only.  Ptrace is unchecked.

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

              This file 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.

              This  file contains the number of filesystems currently mounted.

              This  directory  contains  files   acct,   cad_pid,   cap-bound,
              core_pattern,    core_uses_pid,    ctrl-alt-del,   dentry-state,
              domainname,  hotplug,  hostname,  htab-reclaim  (PowerPC  only),
              java-appletviewer   (binfmt_java,   obsolete),  java-interpreter
              (binfmt_java, obsolete), l2cr (PowerPC only), modprobe,  msgmax,
              msgmnb,  msgmni,  osrelease,  ostype,  overflowgid, overflowuid,
              panic, panic_on_oops,  pid_max,  powersave-nap  (PowerPC  only),
              printk,  pty,  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

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

              This  file holds the value of the kernel capability bounding set
              (expressed as a signed  decimal  number).   This  set  is  ANDed
              against   the   capabilities   permitted  to  a  process  during

              See core(5).

              See core(5).

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

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

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

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

              (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.

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

              This  file  defines  a  system-wide limit specifying the maximum
              number of bytes in a  single  message  written  on  a  System  V
              message queue.

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

              This file defines a system-wide parameter used to initialize the
              msg_qbytes setting for subsequently created message queues.  The
              msg_qbytes  setting  specifies  the maximum number of bytes that
              may be written to the message queue.

       /proc/sys/kernel/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

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

              This file (new in Linux 2.5) 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.

              This file (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.  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.

              The   four   values   in   this   file   are   console_loglevel,
              default_message_loglevel,       minimum_console_level        and
              default_console_loglevel.    These   values  influence  printk()
              behavior when printing or logging error messages.  See syslog(2)
              for  more  info  on  the  different  loglevels.  Messages with a
              higher priority than console_loglevel will  be  printed  to  the
              console.   Messages without an explicit priority will be printed
              with priority  default_message_level.   minimum_console_loglevel
              is  the minimum (highest) value to which console_loglevel can be
              set.   default_console_loglevel  is  the   default   value   for

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

              This file defines the maximum number of pseudo-terminals.

              This read-only file  indicates  how  many  pseudo-terminals  are
              currently in use.

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

              This   file   is   documented   in   the   kernel   source  file

       /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

              (Only in kernels up to and including  2.6.7;  see  setrlimit(2))
              This  file  can  be  used  to  tune  the maximum number of POSIX
              realtime (queued) signals that can be outstanding in the system.

              (Only  in  kernels  up to and including 2.6.7.)  This file shows
              the number POSIX realtime signals currently queued.

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

              SEMMSL  The maximum semaphores per semaphore set.

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

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

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

              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.

              This file contains the system-wide limit on the total number  of
              pages of System V shared memory.

              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.

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

              contains a string like:

                  #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 behind it indicates the time the kernel
              was built.

       /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

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

              This file defines a ceiling value for the  backlog  argument  of
              listen(2); see the listen(2) manual page for details.

              This directory may be empty.

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

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

       /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

              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  >

              Because this is a non-destructive operation  and  dirty  objects
              are not freeable, the user should run sync(8) first.

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

              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 set are not
              checked, and the default check is very weak, leading to the risk
              of  getting a process "OOM-killed".  Under Linux 2.4 any nonzero
              value implies mode 1.  In mode 2 (available  since  Linux  2.6),
              the  total virtual address space on the system is limited to (SS
              + RAM*(r/100)), where SS is the size of the swap space, and  RAM
              is the size of the physical memory, and r is the contents of the
              file /proc/sys/vm/overcommit_ratio.

              See the description of /proc/sys/vm/overcommit_memory.

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

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

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

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

       /proc/vmstat (since Linux 2.6)
              This file displays various virtual memory statistics.

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


       Many strings (i.e., the  environment  and  command  line)  are  in  the
       internal  format,  with  sub-fields 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.


       cat(1),  find(1), free(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),   ifconfig(8),   init(8),   lsmod(8),   lspci(8),  mount(8),
       netstat(8), procinfo(8), route(8)


       This page is part of release 2.77 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at