Ubuntu Manpage: fsck - check and repair a Linux filesystem

Provided by: util-linux_2.20.1-5.1ubuntu20.9_amd64

NAME

       fsck - check and repair a Linux filesystem

SYNOPSIS

       fsck [-lsAVRTMNP] [-C [fd]] [-t fstype] [filesys...]  [--] [fs-specific-options]

DESCRIPTION

fsck is used to check and optionally repair one or more Linux filesystems. 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 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 code 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 - Fsck canceled by user request
128 - Shared-library error
The exit code returned when multiple filesystems are checked is the bit-wise OR of the exit codes 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 /sbin first, then in /etc/fs and /etc,
and finally in the directories listed in the PATH environment variable. Please see the filesystem-
specific checker manual pages for further details.

OPTIONS

-l Lock the whole-disk device by an exclusive flock(2). 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 (8)
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.

-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 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 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 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 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 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 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 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.

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
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'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 filesystem checkers:

-a Automatically repair the filesystem without any questions (use this option with caution). Note
that e2fsck(8) supports -a for backward compatibility only. This option is mapped to e2fsck's -p
option which is safe to use, unlike the -a option that some filesystem 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 backward 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 manually. Note that not all filesystem-specific checkers implement
this option. In particular fsck.minix(8) and fsck.cramfs(8) do not support the -y option as of
this writing.

AUTHOR

       Theodore Ts'o (tytso@mit.edu)

AVAILABILITY

       The    fsck    command    is    part    of    the    util-linux    package    and   is   available   from
       ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

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 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. 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.