fsck

fsck – Filesystem consistency check and repair

The fsck program is a frontend  to filesystem-specific tools such as e2fsck and fsck.jfs. By whatever name, these programs examine a file system’s major data structures for internal consistency and can correct
minor errors.

Generally, fsck is run automatically at boot time

The following example checks the file system on the first partition of the second hard disk on a Linux  system:

 fsck /dev/sdb1

The following example checks the JFS file system on a mdadm software raid device:

 fsck.jfs /dev/md0
fsck [ -sAVRTNP ] [ -C [ fd ] ] [ -t fstype ] [filesys ... ] [--] [ fs-
       specific-options ]

       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.

       -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
              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.

       -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.

       -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

       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.