From Linux Man Pages
fsck - check and repair a Linux file system
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 filesys-
tems 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 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 spec-
ifiers. 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 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 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.
-m Do not check mounted filesystems and return an exit code of 0 for mounted filesystems.
-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 auto-
matically 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 [ 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 informa-
tion will be sent to that file descriptor.
-N Don't execute, just show what would be done.
-M Emulate mount(1) behaviour; do not check the filesystem if it's not listed in /etc/fstab or if fs_pass_no
of the corresponding entry is zero.
-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 driv-
ing the fsck manually. Note that not all filesystem-specific checkers implement this option. In particu-
lar fsck.minix(8) and fsck.cramfs(8) does not support the -y option as of this writing.
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 paral-
lel, regardless of whether the filesystems appear to be on the same device. (This is useful for RAID sys-
tems 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.
BLKID_FILE
This environment variable allows the early boot scripts to override the standard location of the
/etc/blkid.tab file. This file contains a mapping between UUID, LABEL and TYPE values to device nodes.
The information in the blkid.tab might be stale after a reboot if hardware was changed or disks were added
or removed.
RELATED
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).
CATEGORY