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       proc - process information pseudo-filesystem


       The  proc  filesystem  is  a  pseudo-filesystem  which  is  used  as an
       interface to kernel data structures. It is commonly mounted  at  /proc.
       Most  of  it  is read-only, but some files allow kernel variables to be

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

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

              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 link to the current working directory of the process.
              To find out the cwd of process 20,  for  instance,  you  can  do

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

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

              This file contains the environment for the process.  The entries
              are  separated  by  null  characters,  and  there  may be a null
              character 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
              containing the actual path name of the executed  command.   This
              symbolic  link  can be dereferenced normally; attempting to open
              it   will   open   the   executable.    You   can   even    type
              /proc/[number]/exe to run another copy of the same executable as
              is being run by process [number].

              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.

              Programs that will take  a  filename,  but  will  not  take  the
              standard  input,  and  which  write to a file, but will not send
              their output to standard output, can be effectively foiled  this
              way,  assuming that -i is the flag designating an input file and
              -o is the flag designating an output file:

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

              and you have a working filter.

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

              A file containing the currently mapped memory regions and  their
              access permissions.

              The format is:

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

              where  address  is  the  address  space  in  the process that it
              occupies, perms is a set of permissions:

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

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

              Under Linux 2.0 there is no field giving pathname.

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

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

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

              pid %d The process ID.

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

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

              ppid %d
                     The PID of the parent.

              pgrp %d
                     The process group ID of the process.

              session %d
                     The session ID of the process.

              tty_nr %d
                     The tty the process uses.

              tpgid %d
                     The  process group ID of the process which currently owns
                     the tty that the process is connected to.

              flags %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
                     scheduled in user mode.

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

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

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

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

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

              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

              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

              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
              different syntax was named ksyms.

              This file represents the physical memory of the  system  and  is
              stored  in the ELF core file format.  With this pseudo-file, and
              an unstripped kernel (/usr/src/linux/vmlinux) binary, GDB can be
              used to examine the current state of any kernel data structures.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        IP address     HW type   Flags     HW address          Mask   Device   0x1       0x2       00:50:BF:25:68:F3   *      eth0  0x1       0xc       00:00:00:00:00:00   *      eth0

              Here ’IP address’ is the IPv4 address of the machine and the ’HW
              type’  is  the  hardware  type of the address from RFC 826.  The
              flags are the internal flags of the ARP structure (as defined in
              /usr/include/linux/if_arp.h)  and  the  ’HW address’ is the data
              link layer mapping for that IP address if it is known.

              The dev pseudo-file contains network device status  information.
              This  gives  the number of received and sent packets, the number
              of errors and collisions and other basic statistics.  These  are
              used  by  the  ifconfig(8) program to report device status.  The
              format is:

 Inter-|   Receive                                                |  Transmit
  face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
     lo: 2776770   11307    0    0    0     0          0         0  2776770   11307    0    0    0     0       0          0
   eth0: 1215645    2751    0    0    0     0          0         0  1782404    4324    0    0    0   427       0          0
   ppp0: 1622270    5552    1    0    0     0          0         0   354130    5669    0    0    0     0       0          0
   tap0:    7714      81    0    0    0     0          0         0     7714      81    0    0    0     0       0          0

              Defined in /usr/src/linux/net/core/dev_mcast.c:
                   indx interface_name  dmi_u dmi_g dmi_address
                   2    eth0            1     0     01005e000001
                   3    eth1            1     0     01005e000001
                   4    eth2            1     0     01005e000001

              Internet    Group    Management    Protocol.      Defined     in

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

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

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

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

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

              Lists  the  UNIX  domain  sockets  present within the system and
              their status.  The format is:
              Num RefCount Protocol Flags    Type St Path
               0: 00000002 00000000 00000000 0001 03
               1: 00000001 00000000 00010000 0001 01 /dev/printer

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

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

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

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

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

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

              An  echoscsi add-single-device 1 0 5 0> /proc/scsi/scsi will
              cause host scsi1 to scan on SCSI channel 0 for a device on ID  5
              LUN 0. If there is already a device known on this address or the
              address is invalid, an error will be returned.

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

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

              Writing  to  these  files  allows  different things on different
              hosts.  For example, with the latency  and  nolatency  commands,
              root  can  switch on and off command latency measurement code in
              the eata_dma driver. With the lockup and unlock  commands,  root
              can control bus lockups simulated by the scsi_debug driver.

              This  directory  refers  to  the  process  accessing  the  /proc
              filesystem, and is identical to the /proc directory named by the
              process ID of the same process.

              Information about kernel caches.  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 architecures), 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
              subdirectories  abi,  debug,  dev, fs, kernel, net, proc, rxrpc,
              sunrpc and vm that each contain more files and subdirectories.

              This  directory  may  contain  files  with  application   binary
              information.  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  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

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

              This  file contains six numbers, nr_dentry, nr_unused, age_limit
              (age in seconds), want_pages (pages requested by system) and two
              dummy  values.  nr_dentry seems to be 0 all the time.  nr_unused
              seems to be the number of unused dentries.  age_limit is the age
              in  seconds  after  which  dcache  entries can be reclaimed when
              memory is short and want_pages is 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 pageful 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.

              This file specifies the grace period that the kernel grants to a
              process  holding  a  file  lease  (fcntl(2)) after it has sent a
              signal to that process notifying  it  that  another  process  is
              waiting  to  open the file.  If the lease holder does not remove
              or downgrade the lease within  this  grace  period,  the  kernel
              forcibly breaks the lease.

              This  file  can  be  used  to  enable  or  disable  file  leases
              (fcntl(2)) on a system-wide basis.  If this  file  contains  the
              value  0, leases are disabled.  A 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

              This file can be used to view and change the ceiling  value  for
              the maximum number of messages in a queue.  This value acts as a
              ceiling on the attr.mq_maxmsg argument given to mq_open(3).  The
              default  and minimum value for msg_max is 10; the upper limit is
              HARD_MAX: (131072 / sizeof(void *)) (32768 on  Linux/86).   This
              limit  is  ignored  for privileged processes (CAP_SYS_RESOURCE),
              but the HARD_MAX ceiling is nevertheless imposed.

              This file can be used to view and  change  the  ceiling  on  the
              maximum  message  size.   This  value  acts  as a ceiling on the
              attr.mq_msgsize argument given to mq_open(3).  The  default  and
              minimum  value for msgsize_max is 8192 bytes; the upper limit is
              INT_MAX (2147483647 on Linux/86).  This  limit  is  ignored  for
              privileged processes (CAP_SYS_RESOURCE).

              This  file  can be used to view and change the system-wide limit
              on the number of message  queues  that  can  be  created.   Only
              privileged  processes  (CAP_SYS_RESOURCE) can create new message
              queues once this limit has been reached.  The default value  for
              queues_max is 256; it can be changed to any value in the range 0
              to INT_MAX.

       /proc/sys/fs/overflowgid and /proc/sys/fs/overflowuid
              These files allow you to change the value of the fixed  UID  and
              GID.   The  default  is  65534.   Some  filesystems only support
              16-bit UIDs and GIDs, although in Linux UIDs  and  GIDs  are  32
              bits.  When  one  of  these  filesystems  is mounted with writes
              enabled, any UID or GID that would exceed 65535 is translated to
              the overflow value before being written to disk.

       /proc/sys/fs/suid_dumpable (since Linux 2.6.13)
              The  value  in  this file determines whether core dump files are
              produced  for   set-user-ID   or   otherwise   protected/tainted
              binaries.  Three different integer values can be specified:

              0 (default)  This  provides  the  traditional (pre-Linux 2.6.13)
              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
              debugging situations only.  Ptrace is unchecked.

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

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

              This  file contains the number of filesystems currently mounted.

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

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

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

              This  file  (new  in  Linux 2.5) provides finer control over the
              form    of    a    core    filename    than     the     obsolete
              /proc/sys/kernel/core_uses_pid  file  described below.  The name
              for a  core  file  is  controlled  by  defining  a  template  in
              /proc/sys/kernel/core_pattern.    The  template  can  contain  %
              specifiers which are substituted by the following values when  a
              core file is created:

                %%  A single % character
                %p  PID of dumped process
                %u  real UID of dumped process
                %g  real GID of dumped process
                %s  number of signal causing dump
                %t  time of dump (secs since 0:00h, 1 Jan 1970)
                %h  hostname (same as the ’nodename’
                    returned by uname(2))
                %e  executable filename

              A  single  % at the end of the template is dropped from the core
              filename, as is the combination of a % followed by any character
              other  than  those  listed  above.   All other characters in the
              template become a  literal  part  of  the  core  filename.   The
              maximum  size  of  the resulting core filename is 64 bytes.  The
              default  value  in  this   file   is   "core".    For   backward
              compatibility, if /proc/sys/kernel/core_pattern does not include
              "%p" and /proc/sys/kernel/core_uses_pid is non-zero,  then  .PID
              will be appended to the core filename.

              This  file can be used control the naming of a core dump file on
              Linux 2.4.  If this file contains the value 0, then a core  dump
              file  is  simply  named  core.  If this file contains a non-zero
              value, then the core dump file includes the process ID in a name
              of the form core.PID.

              This  file  controls  the  handling  of  Ctrl-Alt-Del  from  the
              keyboard.  When the value in this file  is  0,  Ctrl-Alt-Del  is
              trapped  and  sent  to  the init(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
              syncing its dirty buffers.  Note: when a program  (like  dosemu)
              has  the keyboard in ’raw’ mode, the ctrl-alt-del is intercepted
              by the program before it ever reaches the kernel tty layer,  and
              it’s up to the program to decide what to do with it.

              This  file  contains the path for the hotplug policy agent.  The
              default value in this file "/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
              hostname  "darkstar"  and  DNS  (Internet  Domain  Name  Server)
              domainname "", not to be confused with the NIS  (Network
              Information  Service) or YP (Yellow Pages) domainname. These two
              domain names are in general different. For a detailed discussion
              see the hostname(1) man page.

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

              (PowerPC only) This file contains a flag that  controls  the  L2
              cache  of  G3  processor  boards.  If  0, the cache is disabled.
              Enabled if non-zero.

              This   file   is   described   by   the   kernel   source   file

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

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

              This file defines a system-wide parameter used to 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/kernel/panic file is also non-zero  then  the  machine
              will be rebooted.

              This  file  (new in Linux 2.5) specifies the value at which PIDs
              wrap around (i.e., the value in this file is  one  greater  than
              the  maximum  PID).   The  default  value  for this file, 32768,
              results in the same range of PIDs as  on  earlier  kernels.   On
              32-bit  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_message_loglevel,        minimum_console_level       and
              default_console_loglevel.   These  values   influence   printk()
              behavior  when printing or logging error messages. See syslog(2)
              for more info on  the  different  loglevels.   Messages  with  a
              higher  priority  than  console_loglevel  will be printed to the
              console.  Messages without an explicit priority will be  printed
              with  priority  default_message_level.  minimum_console_loglevel
              is the minimum (highest) value to which console_loglevel can  be
              set.    default_console_loglevel   is   the  default  value  for

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

              This file defines the maximum number of pseudo-terminals.

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

              This  directory  contains  various  parameters  controlling  the
              operation of the file /dev/random.

              This   file   is   documented   in   the   kernel   source  file

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

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

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

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

              SEMMSL  The maximum semaphores per semaphore set.

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

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

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

              This file shows the size of the generic SCSI device (sg) buffer.
              You  can’t  tune it just yet, but you could change it 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/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.    ipc(5)  provides  further  background  on  the
              information shown by these files.

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

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

              This  string  identifies  the  kernel  version that is currently
              running.   It  includes  the   contents   of   /proc/sys/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
              useful 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),
       netstat(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 NUL  bytes,  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)