FSCK(8) System Administration FSCK(8)
fsck - check and repair a Linux filesystem
fsck [-lsAVRTMNP] [-r [fd]] [-C [fd]] [-t fstype] [filesystem...] [--]
fsck is used to check and optionally repair one or more Linux filesys-
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 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 the PATH environment variable. If the PATH
is undefined then fallback to "/sbin".
Please see the filesystem-specific checker manual pages for further
-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
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,
GUI front-ends may specify a file descriptor fd, in which case
the progress bar information will be sent to that file descrip-
tor in a machine parseable format. For example:
/dev/sda1 0 92828 4.002804 2.677592 0.86186
-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.)
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 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 filesystem type (currently ext2) is used.
-A Walk through the /etc/fstab file and try to check all filesys-
tems 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 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 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-exist-
ing devices that have the special filesystem type auto.
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 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 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 com-
mands that are executed.
Options which are not understood by fsck are passed to the
filesystem-specific checker. These options must not take argu-
ments, 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-spe-
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 options 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 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 particu-
lar fsck.minix(8) and fsck.cramfs(8) do not support the -y
option as of this writing.
The fsck 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 used.
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 filesys-
tem checks can be run based on gathering accounting data from
the operating system.
PATH The PATH environment variable is used to find filesystem check-
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.
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), reiserfsck(8).
Theodore Ts'o <firstname.lastname@example.org>
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-
util-linux February 2009 FSCK(8)
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