fsck - check and repair a Linux file system
fsck is used to check and optionally repair one or more Linux
file systems. 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
fsck [-sAVRTMNP] [-C [fd]] [-t fstype] [filesys...] [--] [fs-specific-options]
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
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 details.
- Serialize fsck operations. This is a good idea if you are
checking multiple filesystems and the checkers are in an interactive mode. (Note:
in an interactive mode by default. To make
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 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
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 file system
type (currently ext2) is used.
- Walk through the /etc/fstab file and try to check all file systems
in one run. This option is typically used from the /etc/rc system initialization
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.
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 file system specific checker. Therefore non-existing devices
may cause the system to enter file system 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
file system 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.
- Do not check mounted filesystems and return an exit code of 0 for mounted
- 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
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).
- When checking all file systems with the -A flag, skip the
root file system (in case it's already mounted read-write).
- Don't show the title on startup.
- Produce verbose output, including all file system-specific commands that
- 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 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
option 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 file system checkers:
- Automatically repair the file system without any questions (use this option
with caution). Note that
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 some file system checkers support.
- 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.
- 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.
- 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) does 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
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.)
Note that the fs_passno value is still used.
- 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.
- The PATH environment variable is used to find file system
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
- 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.