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FSCK(8) MAINTENANCE COMMANDS FSCK(8)
NAME
fsck - check and repair a Linux file system
SYNOPSIS
fsck [-sAVRTMNP] [-C [fd]] [-t fstype] [filesys...] [--] [fs-specific-options]
DESCRIPTION
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 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 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 - 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.
OPTIONS
-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 automati-
cally, 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 filesys-
tems 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 argu-
ment to the -t option.
Normally, the filesystem type is deduced by searching for filesys in the /etc/fstab file and using the correspond-
ing 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.
-A 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.
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.
-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 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 commands that are executed.
fs-specific-options
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:
-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 some file system 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 backwards 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 manu-
ally. 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.
AUTHOR
Theodore Ts'o (tytsoATmit.edu)
AVAILABILITY
The fsck command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-
linux-ng/.
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 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.)
FSCK_MAX_INST
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 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.
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), fsck.xiafs(8), reiserfsck(8).
Linux February 2009 FSCK(8)
