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

       proc - process information pseudo-filesystem

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

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

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

	      This holds the complete command line for the process, unless the
	      whole  process  has been swapped out or the process is a zombie.
	      In either of these latter cases, there is nothing in this	 file:
	      i.e.  a read on this file will return 0 characters.  The command
	      line arguments appear in this file as a  set  of	null-separated
	      strings, with a further null byte after the last string.

	      This  is a symbolic link to the current working directory of the
	      process.	To find out the cwd of process 20, for	instance,  you
	      can do this:

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

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

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

	      This file contains the environment for the process.  The entries
	      are  separated  by  null	bytes  ('\0'), and there may be a null
	      bytes at the end.	 Thus, to print out the environment of process
	      1, you would do:

	      (cat /proc/1/environ; echo) | tr "\000" "\n"

	      (For a reason why one should want to do this, see lilo(8).)

	      Under Linux 2.2 and later, this file is a symbolic link contain-
	      ing the actual pathname of the executed command.	This  symbolic
	      link  can	 be  dereferenced normally; attempting to open it will
	      open the executable.  You can even  type	/proc/[number]/exe  to
	      run  another copy of the same executable as is being run by pro-
	      cess [number].  In a multithreaded process, the contents of this
	      symbolic	link  are not available if the main thread has already
	      terminated (typically by calling pthread_exit(3)).

	      Under Linux 2.0 and earlier /proc/[number]/exe is a  pointer  to
	      the binary which was executed, and appears as a symbolic link. A
	      readlink(2) call on this file under Linux 2.0 returns  a	string
	      in the format:


	      For  example, [0301]:1502 would be inode 1502 on device major 03
	      (IDE, MFM, etc. drives) minor 01 (first partition on  the	 first

	      find(1) with the -inum option can be used to locate the file.

	      This  is a subdirectory containing one entry for each file which
	      the process has open, named by its file descriptor, and which is
	      a	 symbolic link to the actual file.  Thus, 0 is standard input,
	      1 standard output, 2 standard error, etc.

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

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

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

	      and you have a working filter.

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

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

	      The format is:

	address		  perms offset	dev   inode	 pathname
	08048000-08056000 r-xp 00000000 03:0c 64593	 /usr/sbin/gpm
	08056000-08058000 rw-p 0000d000 03:0c 64593	 /usr/sbin/gpm
	08058000-0805b000 rwxp 00000000 00:00 0
	40000000-40013000 r-xp 00000000 03:0c 4165	 /lib/ld-2.2.4.so
	40013000-40015000 rw-p 00012000 03:0c 4165	 /lib/ld-2.2.4.so
	4001f000-40135000 r-xp 00000000 03:0c 45494	 /lib/libc-2.2.4.so
	40135000-4013e000 rw-p 00115000 03:0c 45494	 /lib/libc-2.2.4.so
	4013e000-40142000 rw-p 00000000 00:00 0
	bffff000-c0000000 rwxp 00000000 00:00 0

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

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

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

	      Under Linux 2.0 there is no field giving pathname.

	      This  file can be used to access the pages of a process's memory
	      through open(2), read(2), and fseek(3).

	      Unix and Linux support the idea of a  per-process	 root  of  the
	      filesystem,  set	by  the chroot(2) system call.	This file is a
	      symbolic link that points to the process's root  directory,  and
	      behaves as exe, fd/*, etc. do.

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

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

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

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

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

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

	      The fields, in order, with their proper scanf(3)	format	speci-
	      fiers, are:

	      pid %d The process ID.

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

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

	      ppid %d
		     The PID of the parent.

	      pgrp %d
		     The process group ID of the process.

	      session %d
		     The session ID of the process.

	      tty_nr %d
		     The tty the process uses.

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

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

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

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

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

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

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

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

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

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

	      priority %ld
		     (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
	      kernel.  Incidentally, this is used by mount(1) to cycle through
	      different filesystems when none is specified.

	      Empty subdirectory.

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

	      cache		 buffer size in KB
	      capacity		 number of sectors
	      driver		 driver version
	      geometry		 physical and logical geometry
	      identify		 in hexadecimal
	      media		 media type
	      model		 manufacturer's model number
	      settings		 drive settings
	      smart_thresholds	 in hexadecimal
	      smart_values	 in hexadecimal

	      The  hdparm(8)  utility provides access to this information in a
	      friendly format.

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

	      I/O memory map in Linux 2.4.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      Memory  Type  Range   Registers.	  See	/usr/share/doc/kernel-
	      doc-2.6.18/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	struc-
	      tures and are, therefore, readable with cat.  However, the stan-
	      dard netstat(8) suite provides  much  cleaner  access  to	 these

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

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

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

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

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

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

	      Internet	   Group     Management	   Protocol.	 Defined    in

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

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

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

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

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

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

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

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

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

	      This is a listing of all PCI devices found  during  kernel  ini-
	      tialization and their configuration.

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

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

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

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

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

	      Reading these files will usually show driver and host configura-
	      tion, statistics etc.

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

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

	      Information about kernel caches.	The columns are:
	      See slabinfo(5) for details.

	      kernel/system  statistics.   Varies  with	 architecture.	Common
	      entries include:

	      cpu  3357 0 4313 1362393
		     The  amount  of  time,  measured  in  units  of   USER_HZ
		     (1/100ths	of  a  second on most architectures), that the
		     system spent in user mode, user mode  with	 low  priority
		     (nice),  system  mode,  and  the idle task, respectively.
		     The last value should be USER_HZ times the	 second	 entry
		     in the uptime pseudo-file.

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

	      page 5741 1808
		     The number of pages the system paged in  and  the	number
		     that were paged out (from disk).

	      swap 1 0
		     The  number  of  swap pages that have been brought in and

	      intr 1462898
		     This line shows counts of interrupts serviced since  boot
		     time,  for	 each  of the possible system interrupts.  The
		     first column is the total	of  all	 interrupts  serviced;
		     each  subsequent  column  is  the	total for a particular

	      disk_io: (2,0):(31,30,5764,1,2) (3,0):...
		     (major,minor):(noinfo,	 read_io_ops,	    blks_read,
		     write_io_ops, blks_written)
		     (Linux 2.4 only)

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

	      btime 769041601
		     boot time, in seconds since the epoch (January 1,	1970).

	      processes 86031
		     Number of forks since boot.

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

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

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

	      This directory (present since 1.3.57) contains a number of files
	      and subdirectories corresponding	to  kernel  variables.	 These
	      variables can be read and sometimes modified using the proc file
	      system, and the sysctl(2) system call. Presently, there are sub-
	      directories  abi, debug, dev, fs, kernel, net, proc, rxrpc, sun-
	      rpc and vm that each contain more files and subdirectories.

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

	      This directory may be empty.

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

	      This  contains  the  subdirectories  binfmt_misc,	 inotify,  and
	      mqueue,  and  files  dentry-state,  dir-notify-enable, dquot-nr,
	      file-max,	 file-nr,  inode-max,  inode-nr,  inode-state,	lease-
	      break-time,     leases-enable,	 overflowgid,	  overflowuid,
	      suid_dumpable, super-max, and super-nr.

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

	      This  file contains six numbers, nr_dentry, nr_unused, age_limit
	      (age in seconds), want_pages (pages requested by system) and two
	      dummy  values.  nr_dentry seems to be 0 all the time.  nr_unused
	      seems to be the number of unused dentries.  age_limit is the age
	      in seconds after which dcache entries can be reclaimed when mem-
	      ory is short and want_pages is  non-zero	when  the  kernel  has
	      called shrink_dcache_pages() and the dcache isn't pruned yet.

	      This file can be used to disable or enable the dnotify interface
	      described in fcntl(2) on a system-wide basis.  A value of	 0  in
	      this file disables the interface, and a value of 1 enables it.

	      This file shows the maximum number of cached disk quota entries.
	      On some (2.4) systems, it is not present.	 If the number of free
	      cached  disk quota entries is very low and you have some awesome
	      number of simultaneous system users, you might want to raise the

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

	      This file defines a system-wide limit  on	 the  number  of  open
	      files  for  all  processes.   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:

	      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.

	      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
	      (fcntl(2)) on a system-wide basis.  If this  file	 contains  the
	      value  0, leases are disabled.  A non-zero value enables leases.

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

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

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

	      0 (default)  This	 provides  the	traditional (pre-Linux 2.6.13)
	      behaviour.  A core dump will not be produced for a process which
	      has  changed  credentials	 (by calling seteuid(2), setgid(2), or
	      similar, or by executing a set-user-ID or set-group-ID  program)
	      or whose binary does not have read permission enabled.

	      1 ("debug")  All	processes  dump	 core when possible.  The core
	      dump is owned by the file system user ID of the dumping  process
	      and  no security is applied.  This is intended for system debug-
	      ging situations only.  Ptrace is unchecked.

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

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

	      This  file contains the number of filesystems currently mounted.

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

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

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

	      See core(5).  /proc/sys/kernel/core_uses_pid See core(5).

	      This  file  controls  the handling of Ctrl-Alt-Del from the key-
	      board.  When the value  in  this	file  is  0,  Ctrl-Alt-Del  is
	      trapped  and  sent  to  the init(1) program to handle a graceful
	      restart.	When the value is > 0, Linux's reaction	 to  a	Vulcan
	      Nerve Pinch (tm) will be an immediate reboot, without even sync-
	      ing its dirty buffers.  Note: when a program (like  dosemu)  has
	      the  keyboard  in 'raw' mode, the ctrl-alt-del is intercepted by
	      the program before it ever reaches the  kernel  tty  layer,  and
	      it's up to the program to decide what to do with it.

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

       /proc/sys/kernel/domainname and /proc/sys/kernel/hostname
	      can be used to set the NIS/YP domainname	and  the  hostname  of
	      your  box in exactly the same way as the commands domainname and
	      hostname, i.e.:

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

	      has the same effect as

	      # hostname "darkstar"
	      # domainname "mydomain"

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

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

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

	      This  file  is  described	 by  the kernel source file Documenta-

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

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

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

       /proc/sys/kernel/ostype and /proc/sys/kernel/osrelease
	      These files give substrings of /proc/version.

       /proc/sys/kernel/overflowgid and /proc/sys/kernel/overflowuid
	      These  files  duplicate  the  files /proc/sys/fs/overflowgid and

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

	      This file (new in Linux 2.5)  controls  the  kernel's  behaviour
	      when  an	oops  or BUG is encountered.  If this file contains 0,
	      then the system tries to continue operation.  If it contains  1,
	      then  the	 system	 delays	 a  few seconds (to give klogd time to
	      record the oops output) and then panics.	If the	/proc/sys/ker-
	      nel/panic	 file  is  also	 non-zero  then	 the  machine  will be

	      This file (new in Linux 2.5) specifies the value at  which  PIDs
	      wrap  around  (i.e.,  the value in this file is one greater than
	      the maximum PID).	 The  default  value  for  this	 file,	32768,
	      results  in  the	same  range of PIDs as on earlier kernels.  On
	      32-bit platfroms, 32768 is the maximum value  for	 pid_max.   On
	      64-bit  systems,	pid_max	 can  be  set  to any value up to 2^22
	      (PID_MAX_LIMIT, approximately 4 million).

       /proc/sys/kernel/powersave-nap (PowerPC only)
	      This file contains a flag.  If set, Linux-PPC will use the 'nap'
	      mode of powersaving, otherwise the 'doze' mode will be used.

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

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

	      This file defines the maximum number of pseudo-terminals.

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

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

	      This  file  is  documented  in the kernel source file Documenta-

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

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

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

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

	      SEMMSL  The maximum semaphores per semaphore set.

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

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

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

	      This file shows the size of the generic SCSI device (sg) buffer.
	      You can't tune it just yet, but you could change it  on  compile
	      time  by	editing	 include/scsi/sg.h  and	 changing the value of
	      SG_BIG_BUFF.  However, there shouldn't be any reason  to	change
	      this value.

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

	      This file can be used to query and set the run time limit on the
	      maximum  (System	V  IPC) shared memory segment size that can be
	      created.	Shared memory segments up to 1Gb are now supported  in
	      the kernel.  This value defaults to SHMMAX.

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

	      contains a string like:

	      #5 Wed Feb 25 21:49:24 MET 1998.TP

	      The  '#5'	 means	that  this is the fifth kernel built from this
	      source base and the date behind it indicates the time the kernel
	      was built.

       /proc/sys/kernel/zero-paged (PowerPC only)
	      This  file  contains  a flag. When enabled (non-zero), Linux-PPC
	      will pre-zero pages in  the  idle	 loop,	possibly  speeding  up

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

	      This directory may be empty.

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

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

       /proc/sys/vm/drop_caches (since Linux 2.6.16)
	      Writing  to  this	 file  causes the kernel to drop clean caches,
	      dentries and inodes from memory, causing that memory  to	become

	      To  free	pagecache,  use	 echo 1 > /proc/sys/vm/drop_caches; to
	      free dentries and inodes, use echo 2 > /proc/sys/vm/drop_caches;
	      to   free	  pagecache,   dentries	 and  inodes,  use  echo  3  >

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

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

	      This file contains the kernel virtual  memory  accounting	 mode.
	      Values are:
	      0: heuristic overcommit (this is the default)
	      1: always overcommit, never check
	      2: always check, never overcommit
	      In  mode	0,  calls  of  mmap(2)	with MAP_NORESERVE set are not
	      checked, and the default check is very weak, leading to the risk
	      of getting a process "OOM-killed".  Under Linux 2.4 any non-zero
	      value implies mode 1.  In mode 2 (available  since  Linux	 2.6),
	      the  total virtual address space on the system is limited to (SS
	      + RAM*(r/100)), where SS is the size of the swap space, and  RAM
	      is the size of the physical memory, and r is the contents of the
	      file /proc/sys/vm/overcommit_ratio.

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

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

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

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

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

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

       /proc/zoneinfo (since Linux 2.6.13)
	      This  file display information about memory zones.  This is use-
	      ful for analysing virtual memory behaviour.

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

       Note  that many strings (i.e., the environment and command line) are in
       the internal format, with sub-fields terminated by null	bytes  ('\0'),
       so  you	may  find that things are more readable if you use od -c or tr
       "\000" "\n" to read them.  Alternatively, echo 'cat <file>' works well.

       This manual page is incomplete, possibly inaccurate, and is the kind of
       thing that needs to be updated very often.

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

				  2005-05-12			       PROC(5)
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