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.

              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:
              i.e.  a read on this file will return 0 characters.  The command
              line arguments appear in this file as a  set  of  null-separated
              strings, with a further null byte after the last string.

              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).)

              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 pro-
              cess [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/
        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 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 fseek(3).

              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 %lu
                     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).

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

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

              starttime %lu
                     The  time  in  jiffies  the  process 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
                     Signal to be sent to parent when we die.

              processor %d
                     CPU number last executed on.

              rt_priority %lu (since kernel 2.5.19)
                     Real-time  scheduling   priority   (see   sched_setsched-

              policy %lu (since kernel 2.5.19)
                     Scheduling policy (see sched_setscheduler(2)).

              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 kernel 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 were compiled  into  the
              kernel.  Incidentally, this is used by mount(1) to cycle through
              different filesystems when none is specified.

              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)).

              This file is only present if CONFIGDEBUGMALLOC was defined  dur-
              ing compilation.

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

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

              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 ker-
              nel, 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  "remote address" is the
              remote address and port number pair (if connected). 'St' is  the
              internal  status  of  the socket.  The 'tx_queue' and 'rx_queue'
              are the outgoing and incoming data queue in terms of kernel mem-
              ory  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  "remote address" is the
              remote address and port number pair (if connected). "St" is  the
              internal  status  of  the socket.  The "tx_queue" and "rx_queue"
              are the outgoing and incoming data queue in terms of kernel mem-
              ory  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.

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

              You can also write to some of the files to 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.  The columns 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).

              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 sub-
              directories abi, debug, dev, fs, kernel, net, proc, rxrpc,  sun-
              rpc and vm that each contain more files and subdirectories.

              This  directory may contain files with application binary infor-
              mation.  On some systems, it is not present.

              This directory may be empty.

              This  directory  contains  device   specific   information   (eg
              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 non-zero 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 non-zero 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 non-zero 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)
              behaviour.  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 behaviour. 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 exec().

              See core(5).  /proc/sys/kernel/core_uses_pid 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(1) program to handle a graceful
              restart.  When the value is > 0, Linux's reaction  to  a  Vulcan
              Nerve Pinch (tm) will be an immediate reboot, 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 "/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 and
              hostname, i.e.:

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

              has the same effect as

              # hostname "darkstar"
              # domainname "mydomain"

              Note, however, that the classic has the  host-
              name "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 non-zero 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 non-zero.

              This  file  is  described  by  the kernel source file Documenta-

              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 initialise 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 non-zero 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  behaviour
              when  an  oops  or BUG is encountered.  If this file contains 0,
              then the system tries to continue operation.  If it contains  1,
              then  the  system  delays  a  few seconds (to give klogd time to
              record the oops output) and then panics.  If the  /proc/sys/ker-
              nel/panic  file  is  also  non-zero  then  the  machine  will be

              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 platfroms, 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_con-
              sole_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 reboot-

              (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  on  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.TP

              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 (non-zero), 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 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  non-zero, 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 non-zero
              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/ostype,
              /proc/sys/osrelease and /proc/sys/version.  For example:
            Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994

       /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 analysing virtual memory behaviour.

       cat(1), find(1), free(1), mount(1), ps(1), tr(1), uptime(1), chroot(2),
       mmap(2),   readlink(2),   syslog(2),   slabinfo(5),   hier(7),  arp(8),
       dmesg(8), hdparm(8), ifconfig(8),  init(8),  lsmod(8),  lspci(8),  net-
       stat(8), procinfo(8), route(8)

       Note  that 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.

       The material on /proc/sys/fs and /proc/sys/kernel is closely  based  on
       kernel source documentation files written by Rik van Riel.

                                  2005-05-12                           PROC(5)

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