fsck - check and repair a Linux file system

fsck [ -sACVRTNP ] [ -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 run filesystems on different physi-
cal disk drives in parallel to reduce total amount time 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 serial. 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

-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
fslist are not prefixed by a negation operator, then only those
filesystems listed in fslist 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 file system type (currently ext2) is

-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 initalization 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 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.

-C Display completion/progress bars for those filesystems checkers
(currently only for ext2) which support them. Fsck will manage
the filesystem checkers so that only one of them will display a
progress bar at a time.

-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 file systems with the -A flag, skip the root
file system (in case it's already mounted read-write).

-T Don't show the title on startup.

-V Produce verbose output, including all file system-specific com-
mands that are executed.

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

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.

Currently, standardized file system-specific options are somewhat in
flux. 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 most
file system checkers support.

-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.

Theodore Ts'o ([email protected])


The fsck program's behavior is affected by the following environment

If this environment variable is set, fsck will attempt to run
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.)

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

PATH The PATH environment variable is used to find file system check-
ers. A set of system directories are searched first: /sbin,
/sbin/fs.d, /sbin/fs, /etc/fs, and /etc. Then the set of direc-
tories found in the PATH environment are searched.

This environment variable allows the system administrator to
override the standard location of the /etc/fstab file. It is
also use for developers who are testing fsck.