fsck - check and repair a Linux filesystem
is used to check and optionally repair one or more Linux
can be a device name (e.g. /dev/hdc1
), a mount point (e.g. /
or an ext2 label or UUID specifier (e.g.
UUID=8868abf6-88c5-4a83-98b8-bfc24057f7bd or LABEL=root). Normally, the
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
If no filesystems are specified on the command line, and the -A
not specified, fsck
will default to checking filesystems in
serially. This is equivalent to the -As
The exit code returned by fsck
is the sum of the following conditions:
- No errors
- Filesystem errors corrected
- System should be rebooted
- Filesystem errors left uncorrected
- Operational error
- Usage or syntax error
- Checking canceled by user request
- 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
) available under Linux. The
filesystem-specific checker is searched for in the PATH environment variable.
If the PATH is undefined then fallback to "/sbin".
Please see the filesystem-specific checker manual pages for further details.
- 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 [fd]
- 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
GUI front-ends may specify a file descriptor fd, in which case the
progress bar information will be sent to that file descriptor in a machine
parsable format. For example:
/dev/sda1 0 92828 4.002804 2.677592 0.86186
- 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
- -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
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
cannot 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.
- 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 determine dependencies between
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) 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
- Do not check mounted filesystems and return an exit code of
0 for mounted filesystems.
- Don't execute, just show what would be done.
- 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
- 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.)
- Don't show the title on startup.
- Produce verbose output, including all filesystem-specific
commands that are executed.
- -?, --help
- Display help text and exit.
Options which are not understood by fsck are passed to the
- Display version information and exit.
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.
almost certainly doing something that you shouldn't be doing with fsck
Options to different filesystem-specific fsck's are not standardized.
program's behavior is affected by the following environment
- 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
- 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.
- The PATH environment variable is used to find
- 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.
- enables libblkid debug output.
- enables libmount debug output.
Theodore Ts'o <firstname.lastname@example.org>
Karel Zak <email@example.com>
The fsck command is part of the util-linux package and is available from