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-


              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

              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:


              (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:


              and you have a working filter.

              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
        08058000-0805b000 rwxp 00000000 00:00 0
        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

                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).

              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

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

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

              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.

              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)).

              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 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
              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

              friendly format.

              (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
              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
              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.

              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-


       /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
              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

              leases (fcntl(2)).

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

              shared memory and buffers used by the kernel.


              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.

              See also lsmod(8).

              Memory  Type  Range   Registers.    See   /usr/share/doc/kernel-
              doc-2.6.18/Documentation/mtrr.txt for details.

              part of the networking layer.  These files contain ASCII  struc-
              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:


              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

              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
              remote  address and port number pair (if connected). "St" is the
              internal status of the socket.  The  "tx_queue"  and  "rx_queue"
              used  by  UDP.   The  "uid" field holds the effective UID of the
              creator of the socket.  The format is:


              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

              'Flags'  represent  the internal kernel flags holding the status
              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.

              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
              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
                     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:
                     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

                     write_io_ops, blks_written)
                     (Linux 2.4 only)

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

              btime 769041601

              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
              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

              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.

              files  for  all  processes.   This limit is not applied to root.
              (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 value:


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


              Historically, the three values in file-nr denoted the number  of
              allocated  file handles, the number of allocated but unused file
              handles, and the maximum  number  of  file  handles.  Linux  2.6
              always  reports  0 as the number of free file handles -- this is
              not an error, it just means that the number  of  allocated  file
              handles exactly matches the number of used file handles.

              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
              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.

              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
              the program before it ever reaches the  kernel  tty  layer,  and

              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 "mydomain" > /proc/sys/kernel/domainname

              has the same effect as

              # hostname "darkstar"
              # domainname "mydomain"

              Note, however, that the classic has the  host-
              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
              Enabled if non-zero.

              This  file  is  described  by  the kernel source file Documenta-

              This file defines a system-wide  limit  specifying  the  maximum
              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
              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
              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.

                      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
              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:


              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;

              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
              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 string identifies the kernel version that is currently run-

       /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.

       dmesg(8), hdparm(8), ifconfig(8),  init(8),  lsmod(8),  lspci(8),  net-
       stat(8), procinfo(8), route(8)

       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.

       thing that needs to be updated very often.

       kernel source documentation files written by Rik van Riel.

                                  2005-05-12                           PROC(5)