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FSCK(8)                               System Administration                               FSCK(8)



NAME
       fsck - check and repair a Linux filesystem

SYNOPSIS
       fsck [-lrsAVRTMNP] [-C [fd]] [-t fstype] [filesystem...]  [--] [fs-specific-options]

DESCRIPTION
       fsck is used to check and optionally repair one or more Linux filesystems.  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).  Normally, the fsck program will try to handle filesystems on different phys-
       ical  disk  drives  in  parallel to reduce the total amount of time needed to check all of
       them.

       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      Filesystem errors corrected
              2      System should be rebooted
              4      Filesystem errors left uncorrected
              8      Operational error
              16     Usage or syntax error
              32     Checking canceled by user request
              128    Shared-library error

       The exit code returned when multiple filesystems are checked is the  bit-wise  OR  of  the
       exit codes for each filesystem that is checked.

       In actuality, fsck is simply a front-end for the various filesystem checkers (fsck.fstype)
       available under Linux.  The filesystem-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 filesystem-specific checker manual pages for further details.

OPTIONS
       -l     Lock the whole-disk device by an exclusive flock(2).  This option can be used  with
              one device only (this means that -A and -l are mutually exclusive).  This option is
              recommended when more fsck(8) instances are executed in the same time.  The  option
              is ignored when used for multiple devices or for non-rotating disks.  fsck does not
              lock underlying devices when executed to check stacked devices (e.g. MD or  DM)  --
              this feature is not implemented yet.

       -r     Report certain statistics for each fsck when it completes. These statistics include
              the exit status, the maximum run set size (in  kilobytes),  the  elapsed  all-clock
              time and the user and system CPU time used by the fsck run. For example:

              /dev/sda1: status 0, rss 92828, real 4.002804, user 2.677592, sys 0.86186

       -s     Serialize  fsck  operations.   This  is  a  good  idea if you are checking multiple
              filesystems and the checkers are in an interactive 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 filesystem 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 none
              of the filesystems in fslist is prefixed by a negation operator,  then  only  those
              listed filesystems 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  filesys-
              tems  which  contain  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 single filesystem given as an argument to the -t option,  fsck  will  use
              the  specified  filesystem  type.   If this type is not available, then the default
              filesystem type (currently ext2) is used.

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

              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 low-
              est  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.

              fsck  does  not  check  stacked devices (RAIDs, dm-crypt, ...) in parallel with any
              other device.  See below for FSCK_FORCE_ALL_PARALLEL setting.  The /sys  filesystem
              is used to detemine dependencies between devices.

              Hence,  a very common configuration in /etc/fstab files is to set the root filesys-
              tem 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 check-
              ers in parallel if it is advantageous to do so.  System administrators might choose
              not to use this configuration if they need to avoid multiple filesystem checks run-
              ning 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
              filesystem specific checker.  Therefore non-existing devices may cause  the  system
              to  enter  filesystem  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 spe-
              cial filesystem 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
              specify  a  file  descriptor fd, in which case the progress bar information will be
              sent to that file descriptor.

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

       -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  repartition
              the root filesystem to be small and compact (which is really the right solution).

       -R     When checking all filesystems with the -A flag, skip the root filesystem.  (This is
              useful in case the root filesystem has already been mounted read-write.)

       -T     Don't show the title on startup.

       -V     Produce verbose output, including all filesystem-specific commands  that  are  exe-
              cuted.

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

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

              Please note that fsck is not designed to pass arbitrarily  complicated  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
              complicated  options and arguments, and it doesn't do what you expect, don't bother
              reporting it as a bug.  You're almost certainly 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 filesystem checkers:

       -a     Automatically  repair  the  filesystem  without any questions (use this option with
              caution).  Note that e2fsck(8) supports -a for backward compatibility  only.   This
              option  is  mapped to e2fsck's -p option which is safe to use, unlike the -a option
              that some filesystem 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 partic-
              ular,  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  backward
              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   particular
              fsck.minix(8) and fsck.cramfs(8) do not support the -y option as of this writing.

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 check all of the speci-
              fied 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.)  Note that the fs_passno  value  is
              still used.

       FSCK_MAX_INST
              This environment variable will limit the maximum number of filesystem checkers that
              can be running at one time.  This allows configurations which have a  large  number
              of  disks  to avoid fsck starting too many filesystem 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 filesystem checks can be run based on gathering accounting data from the oper-
              ating system.

       PATH   The PATH environment variable is used to find filesystem checkers.  A set of system
              directories  are  searched  first:  /sbin, /sbin/fs.d, /sbin/fs, /etc/fs, and /etc.
              Then the set of directories 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.

       LIBBLKID_DEBUG=0xffff
              enables debug output.

       LIBMOUNT_DEBUG=0xffff
              enables debug output.

SEE ALSO
       fstab(5), mkfs(8), fsck.ext2(8) or fsck.ext3(8) or e2fsck(8), cramfsck(8),  fsck.minix(8),
       fsck.msdos(8),  fsck.jfs(8),  fsck.nfs(8), fsck.vfat(8), fsck.xfs(8), fsck.xiafs(8), reis-
       erfsck(8).

AUTHOR
       Theodore Ts'o <tytso AT mit.edu>

AVAILABILITY
       The fsck command is part of the util-linux package and  is  available  from  Linux  Kernel
       Archive <ftp://ftp.kernel.org/pub/linux/utils/util-linux/>.



util-linux                                February 2009                                   FSCK(8)

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