FSCK

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 physical 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     Create an exclusive flock(2) lock file
(/run/fsck/<diskname>.lock) for whole-disk device.  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 filesystems 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 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.

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 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 multiple 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 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 special
filesystem type auto.

-C [fd]
Display completion/progress bars for those filesystem checkers
(currently only for ext[234]) 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 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 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 executed.

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
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
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 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.)  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 operating 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=all
enables libblkid debug output.

LIBMOUNT_DEBUG=all
enables libmount 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), reiserfsck(8).

AUTHOR

Theodore Ts’o ⟨[email protected]

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/⟩.

COLOPHON

This page is part of the util-linux (a random collection of Linux
utilities) project.  Information about the project can be found at
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you have a
bug report for this manual page, send it to
[email protected]  This page was obtained from the
project’s upstream Git repository
(git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git) on
2014-12-30.  If you discover any rendering problems in this HTML ver‐
sion of the page, or you believe there is a better or more up-to-date
source for the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original man‐
ual page), send a mail to [email protected]

util-linux                      February 2009                        FSCK(8)

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