fsck - check and repair a Linux filesystem

       Theodore Ts’o <tytso@mit.edu>, Karel Zak <kzak@redhat.com>

       The fsck command is part of the util-linux package which can be downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.41                                    2025-02-26                                            FSCK(8)

fsck is used to check and optionally repair one or more Linux filesystems. filesystem can be a device
       name (e.g., /dev/hdc1, /dev/sdb2), a mount point (e.g., /, /usr, /home), or a filesystem 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 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 status 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 status returned when multiple filesystems are checked is the bit-wise OR of the exit statuses
       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 details.

       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 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.

       FSCK_MAX_INST
           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
           filesystem checks can be run based on gathering accounting data from the operating system.

       PATH
           The PATH environment variable is used to find filesystem checkers.

       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.

       LIBBLKID_DEBUG=all
           enables libblkid debug output.

       LIBMOUNT_DEBUG=all
           enables libmount debug output.

/etc/fstab

Optionswhicharenotunderstoodbyfsckarepassedtothefilesystem-specificchecker!

       These options must not take arguments, 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-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 options and arguments, and it doesn’t do what you
       expect, don’tbotherreportingitasabug. You’re almost certainly doing something that you shouldn’t be
       doing with fsck. Options to different filesystem-specific fsck’s are not standardized.

       fsck - check and repair a Linux filesystem

       During boot, systemd does not invoke fsck-A. Instead, it schedules the activation of mounts
       individually, taking into account dependencies on backing devices, networking, and other factors.
       Consequently, fsck is called individually for each device.

-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 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 implemented yet.

       -r [fd]
           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:status0,rss92828,real4.002804,user2.677592,sys0.86186

           GUI front-ends may specify a file descriptor fd, in which case the progress bar information will be
           sent to that file descriptor in a machine parsable format. For example:

           /dev/sda10928284.0028042.6775920.86186-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.)

       -tfslist
           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 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 cannot 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 filesystem type (currently ext2) is used.

       -A
           Walk through the /etc/fstab file and try to check all filesystems 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 determine 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 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-existing devices that have the
           special filesystem type auto.

       -C [fd]
           Display completion/progress bars for those filesystem checkers (currently only for ext[234]) 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 status 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 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 commands that are executed.

       -?, --help
           Display help text and exit.

       --version
           Display version information and exit.

       For bug reports, use the issue tracker <https://github.com/util-linux/util-linux/issues>.

fstab(5), mkfs(8), fsck.ext2(8) or fsck.ext3(8) or e2fsck(8), fsck.cramfs(8), fsck.jfs(8), fsck.nfs(8),
       fsck.minix(8), fsck.msdos(8), fsck.vfat(8), fsck.xfs(8), reiserfsck(8)

fsck [-lsAVRTMNP] [-r [fd]] [-C [fd]] [-tfstype] [filesystem...] [--] [fs-specific-options]