fsck man page on aLinux

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FSCK(8)			     MAINTENANCE COMMANDS		       FSCK(8)

NAME
       fsck - check and repair a Linux file system

SYNOPSIS
       fsck [-sAVRTMNP] [-C [fd]] [-t fstype] [filesys...]  [--] [fs-specific-
       options]

DESCRIPTION
       fsck is used to check and optionally repair one or more Linux file sys‐
       tems.   filesys	can  be	 a device name (e.g.  /dev/hdc1, /dev/sdb2), a
       mount point (e.g.  /, /usr, /home), or an ext2 label or UUID  specifier
       (e.g.   UUID=8868abf6-88c5-4a83-98b8-bfc24057f7bd or LABEL=root).  Nor‐
       mally, the fsck program will try to  handle  filesystems	 on  different
       physical	 disk  drives  in  parallel to reduce the total amount of time
       needed to check all of the filesystems.

       If no filesystems are specified on the command line, and the -A	option
       is  not	specified,  fsck  will	default	 to  checking  filesystems  in
       /etc/fstab serially.  This is equivalent to the -As options.

       The exit code returned by fsck is the sum of the following conditions:
	    0	 - No errors
	    1	 - File system errors corrected
	    2	 - System should be rebooted
	    4	 - File system errors left uncorrected
	    8	 - Operational error
	    16	 - Usage or syntax error
	    32	 - Fsck canceled by user request
	    128	 - Shared library error
       The exit code returned when multiple file systems are  checked  is  the
       bit-wise OR of the exit codes for each file system that is checked.

       In  actuality,  fsck  is simply a front-end for the various file system
       checkers (fsck.fstype) available under Linux.  The file system-specific
       checker	is  searched for in /sbin first, then in /etc/fs and /etc, and
       finally in the directories listed in  the  PATH	environment  variable.
       Please  see  the	 file system-specific checker manual pages for further
       details.

OPTIONS
       -s     Serialize fsck operations.  This is  a  good  idea  if  you  are
	      checking	multiple filesystems and the checkers are in an inter‐
	      active mode.  (Note: e2fsck(8) runs in an	 interactive  mode  by
	      default.	 To  make e2fsck(8) run in a non-interactive mode, you
	      must either specify the -p or -a option, if you wish for	errors
	      to be corrected automatically, or the -n option if you do not.)

       -t fslist
	      Specifies the type(s) of file system to be checked.  When the -A
	      flag is  specified,  only	 filesystems  that  match  fslist  are
	      checked.	 The  fslist  parameter	 is  a comma-separated list of
	      filesystems and options specifiers.  All of the  filesystems  in
	      this comma-separated list may be prefixed by a negation operator
	      'no' or '!', which requests  that	 only  those  filesystems  not
	      listed  in fslist will be checked.  If all of the filesystems in
	      fslist are not prefixed by a negation operator, then only	 those
	      filesystems listed in fslist will be checked.

	      Options  specifiers  may	be  included  in  the  comma-separated
	      fslist.  They  must  have	 the  format  opts=fs-option.	If  an
	      options  specifier  is present, then only filesystems which con‐
	      tain fs-option in their mount options field of  /etc/fstab  will
	      be  checked.  If the options specifier is prefixed by a negation
	      operator, then only those filesystems that do not have fs-option
	      in their mount options field of /etc/fstab will be checked.

	      For example, if opts=ro appears in fslist, then only filesystems
	      listed in /etc/fstab with the ro option will be checked.

	      For compatibility with Mandrake distributions whose boot scripts
	      depend  upon an unauthorized UI change to the fsck program, if a
	      filesystem type of loop is found in fslist, it is treated as  if
	      opts=loop were specified as an argument to the -t option.

	      Normally,	 the  filesystem  type	is  deduced  by	 searching for
	      filesys in the  /etc/fstab  file	and  using  the	 corresponding
	      entry.  If the type can not be deduced, and there is only a sin‐
	      gle filesystem given as an argument to the -t option, fsck  will
	      use  the	specified filesystem type.  If this type is not avail‐
	      able, then the default file  system  type	 (currently  ext2)  is
	      used.

       -A     Walk  through the /etc/fstab file and try to check all file sys‐
	      tems in one run.	This option is typically used from the /etc/rc
	      system  initialization  file,  instead  of multiple commands for
	      checking a single file system.

	      The root filesystem will be checked first unless the  -P	option
	      is  specified  (see  below).   After  that,  filesystems will be
	      checked in the order specified  by  the  fs_passno  (the	sixth)
	      field  in	 the  /etc/fstab  file.	  Filesystems with a fs_passno
	      value of 0 are skipped and are not checked at all.   Filesystems
	      with  a  fs_passno value of greater than zero will be checked in
	      order, with filesystems with the lowest fs_passno	 number	 being
	      checked  first.  If there are multiple filesystems with the same
	      pass number, fsck	 will  attempt	to  check  them	 in  parallel,
	      although it will avoid running multiple filesystem checks on the
	      same physical disk.

	      Hence, a very common configuration in /etc/fstab files is to set
	      the  root	 filesystem  to have a fs_passno value of 1 and to set
	      all other filesystems to have a fs_passno value of 2.  This will
	      allow  fsck to automatically run filesystem checkers in parallel
	      if it is advantageous to do  so.	 System	 administrators	 might
	      choose  not to use this configuration if they need to avoid mul‐
	      tiple filesystem checks running in parallel for some reason  ---
	      for  example,  if	 the machine in question is short on memory so
	      that excessive paging is a concern.

	      fsck normally does not check whether the device actually	exists
	      before  calling  a  file system specific checker. Therefore non-
	      existing devices may cause  the  system  to  enter  file	system
	      repair  mode  during  boot  if  the  filesystem specific checker
	      returns a fatal error. The /etc/fstab mount option nofail may be
	      used  to	have  fsck skip non-existing devices.  fsck also skips
	      non-existing devices that have the special file system type auto

       -C [  fd	 ]
	      Display completion/progress bars for those  filesystem  checkers
	      (currently  only	for  ext2 and ext3) which support them.	  Fsck
	      will manage the filesystem checkers so that  only	 one  of  them
	      will display a progress bar at a time.  GUI front-ends may spec‐
	      ify a file descriptor fd, in which case the progress bar	infor‐
	      mation will be sent to that file descriptor.

       -M     Do  not  check  mounted filesystems and return an exit code of 0
	      for mounted filesystems.

       -N     Don't execute, just show what would be done.

       -P     When the -A flag is set, check the root filesystem  in  parallel
	      with the other filesystems.  This is not the safest thing in the
	      world to do, since if the root filesystem	 is  in	 doubt	things
	      like  the	 e2fsck(8) executable might be corrupted!  This option
	      is mainly provided for those sysadmins who don't want to	repar‐
	      tition  the  root	 filesystem  to be small and compact (which is
	      really the right solution).

       -R     When checking all file systems with the -A flag, skip  the  root
	      file system (in case it's already mounted read-write).

       -T     Don't show the title on startup.

       -V     Produce  verbose output, including all file system-specific com‐
	      mands that are executed.

       fs-specific-options
	      Options which are not understood	by  fsck  are  passed  to  the
	      filesystem-specific  checker.   These  arguments	must  not take
	      arguments, as there is no way for fsck to be  able  to  properly
	      guess which arguments take options and which don't.

	      Options  and  arguments  which follow the -- are treated as file
	      system-specific options to be passed to the file system-specific
	      checker.

	      Please  note  that fsck is not designed to pass arbitrarily com‐
	      plicated options to  filesystem-specific	checkers.   If	you're
	      doing something complicated, please just execute the filesystem-
	      specific checker directly.  If you pass fsck some horribly  com‐
	      plicated	option	and  arguments,	 and  it  doesn't  do what you
	      expect, don't bother reporting it as a bug.  You're almost  cer‐
	      tainly doing something that you shouldn't be doing with fsck.

       Options	to  different filesystem-specific fsck's are not standardized.
       If in doubt, please consult the man pages  of  the  filesystem-specific
       checker.	  Although not guaranteed, the following options are supported
       by most file system checkers:

       -a     Automatically repair the file system without any questions  (use
	      this  option with caution).  Note that e2fsck(8) supports -a for
	      backwards compatibility only.  This option is mapped to e2fsck's
	      -p  option  which is safe to use, unlike the -a option that some
	      file system checkers support.

       -n     For some filesystem-specific checkers, the -n option will	 cause
	      the fs-specific fsck to avoid attempting to repair any problems,
	      but simply report such problems to stdout.  This is however  not
	      true  for	 all  filesystem-specific  checkers.   In  particular,
	      fsck.reiserfs(8) will not report any corruption  if  given  this
	      option.  fsck.minix(8) does not support the -n option at all.

       -r     Interactively  repair  the  filesystem  (ask for confirmations).
	      Note: It is generally a bad idea to use this option if  multiple
	      fsck's  are  being  run  in  parallel.   Also  note that this is
	      e2fsck's default behavior; it supports this option for backwards
	      compatibility reasons only.

       -y     For  some filesystem-specific checkers, the -y option will cause
	      the fs-specific fsck to  always  attempt	to  fix	 any  detected
	      filesystem corruption automatically.  Sometimes an expert may be
	      able to do better driving the fsck manually.  Note that not  all
	      filesystem-specific checkers implement this option.  In particu‐
	      lar fsck.minix(8) and fsck.cramfs(8) does	 not  support  the  -y
	      option as of this writing.

AUTHOR
       Theodore Ts'o (tytso@mit.edu)

AVAILABILITY
       The blkid command is part of the util-linux-ng package and is available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.

FILES
       /etc/fstab.

ENVIRONMENT VARIABLES
       The fsck program's behavior is affected by  the	following  environment
       variables:

       FSCK_FORCE_ALL_PARALLEL
	      If  this	environment  variable is set, fsck will attempt to run
	      all of the specified  filesystems	 in  parallel,	regardless  of
	      whether  the filesystems appear to be on the same device.	 (This
	      is useful for RAID systems or high-end storage systems  such  as
	      those sold by companies such as IBM or EMC.)

       FSCK_MAX_INST
	      This  environment variable will limit the maximum number of file
	      system checkers that can be running at one  time.	  This	allows
	      configurations  which have a large number of disks to avoid fsck
	      starting too many file system  checkers  at  once,  which	 might
	      overload	CPU  and memory resources available on the system.  If
	      this value is zero, then an unlimited number of processes can be
	      spawned.	 This is currently the default, but future versions of
	      fsck may attempt to automatically determine how many file system
	      checks  can  be  run based on gathering accounting data from the
	      operating system.

       PATH   The PATH environment variable is used to find file system check‐
	      ers.   A	set  of	 system directories are searched first: /sbin,
	      /sbin/fs.d, /sbin/fs, /etc/fs, and /etc.	Then the set of direc‐
	      tories found in the PATH environment are searched.

       FSTAB_FILE
	      This  environment	 variable  allows  the system administrator to
	      override the standard location of the /etc/fstab	file.	It  is
	      also useful for developers who are testing fsck.

SEE ALSO
       fstab(5),  mkfs(8),  fsck.ext2(8)  or fsck.ext3(8) or e2fsck(8), cramf‐
       sck(8),	 fsck.minix(8),	  fsck.msdos(8),   fsck.jfs(8),	  fsck.nfs(8),
       fsck.vfat(8), fsck.xfs(8), fsck.xiafs(8), reiserfsck(8).

Linux				 February 2009			       FSCK(8)
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