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

       proc - process information pseudo-filesystem

       The  proc  filesystem is a pseudo-filesystem which is used as an inter-
       face 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 com-
              mand  line  arguments appear in this file as a set of null-sepa-
              rated strings, with a further null byte after the last string.

              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 contain-
              ing the actual pathname of the executed command.  This  symbolic
              link  can  be  dereferenced normally; attempting to open it will
              open the executable.  You can even  type  /proc/[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 pthread_exit(3)).

              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 (typi-
              cally by calling pthread_exit(3)).

              Programs that will take a filename, but will not take the  stan-
              dard  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 symboli-
              cally 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/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 occu-
              pies, 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 indi-
              cates 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 dis-
              played 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 pri-
              vate 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  speci-
              fiers, 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  run-
                     ning,  S is sleeping in an interruptible wait, D is wait-
                     ing 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  sched-
                     uled in user mode.

              stime %lu
                     The  number  of jiffies that this process has been sched-
                     uled 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  sched_setsched-

              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/[num-
              ber] 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/[num-
              ber]/task directory are not available if  the  main  thread  has
              already terminated (typically by calling pthread_exit(3)).

              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 filesys-
              tems(5).)   If  a  filesystem is marked with "nodev", this means
              that it does not require a block device  to  be  mounted  (e.g.,
              virtual filesystem, network filesystem).

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

              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  dif-
              ferent 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 mes-

              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  sepa-
              rated  by a slash (/).  The first of these is the number of cur-
              rently  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 open-
              ing 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/Documenta-
              tion/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  struc-
              tures and are, therefore, readable with cat.  However, the stan-
              dard 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  ker-
              nel  hash  slot for the socket, the 'local_address' is the local
              address and protocol number pair. "St" is the internal status of
              the  socket.  The "tx_queue" and "rx_queue" are the outgoing and
              incoming data queue in terms of kernel memory usage.  The  "tr",
              "tm->when", and "rexmits" fields are not used by RAW.  The "uid"
              field holds the effective UID of the creator of the socket.

              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  ker-
              nel  hash  slot for the socket, the "local_address" is the local
              address and port number pair.  The "rem_address" is  the  remote
              address  and port number pair (if connected). 'St' is the inter-
              nal status of the socket.  The 'tx_queue' and 'rx_queue' are the
              outgoing  and  incoming  data  queue  in  terms of kernel memory
              usage.  The "tr", "tm->when", and "rexmits" fields hold internal
              information  of  the kernel socket state and are only useful for
              debugging.  The "uid" field holds the effective UID of the  cre-
              ator 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  ker-
              nel  hash  slot for the socket, the "local_address" is the local
              address and port number pair.  The "rem_address" is  the  remote
              address  and port number pair (if connected). "St" is the inter-
              nal status of the socket.  The "tx_queue" and "rx_queue" are the
              outgoing  and  incoming  data  queue  in  terms of kernel memory
              usage.  The "tr", "tm->when", and "rexmits" fields are not  used
              by  UDP.  The "uid" field holds the effective UID of the creator
              of the socket.  The format is:

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

              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 data-
              gram  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  ini-
              tialization and their configuration.

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

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

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

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

              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.

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

              Reading these files will usually show driver and host configura-
              tion, statistics 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  infor-
              mation.  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 mem-
              ory  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 inter-
              face.  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 sig-
              nal to that process notifying it that another process is waiting
              to  open the file.  If the lease holder does not remove or down-
              grade 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 bina-
              ries.  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  debug-
              ging 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 adminis-
              trators are attempting to debug problems in  a  normal  environ-

              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, domain-
              name,  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 fre-
              quency.  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.  Fre-
              quency 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 key-
              board.  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 sync-
              ing 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 darkstar.frop.org has the  host-
              name "darkstar" and DNS (Internet Domain Name Server) domainname
              "frop.org", not to be confused with the NIS (Network Information
              Service)  or  YP  (Yellow  Pages)  domainname.  These two domain
              names are in general different.  For a detailed  discussion  see
              the hostname(1) man page.

              (PowerPC  only) If this file is set to a nonzero value, the Pow-
              erPC 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  mes-
              sage 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_mes-
              sage_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  con-

       /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 cur-
              rently in use.

              This directory contains various parameters controlling the oper-
              ation of the file /dev/random.  See random(4) for further infor-

              This  file  is  documented  in the kernel source file Documenta-

       /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 real-
              time (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 (sec-
              onds), and the amount of time spent in idle process (seconds).

              This string identifies the kernel version that is currently run-
              ning.   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 use-
              ful for analyzing virtual memory behavior.

       Many strings (i.e., the environment and command line) are in the inter-
       nal 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),  net-
       stat(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 http://www.kernel.org/doc/man-pages/.

Linux                             2007-11-30                           PROC(5)