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FSCK(8) |
System Administration |
FSCK(8) |
fsck - check and repair a Linux filesystem
fsck [-lrsAVRTMNP] [-C [fd]] [-t
fstype] [filesystem...] [--] [fs-specific-options]
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
- Checking 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.
- -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.
- -r
- 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: status 0, rss 92828, real 4.002804, user 2.677592,
sys 0.86186
- -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.)
- -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 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'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.
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.
- LIBBLKID_DEBUG=0xffff
- enables debug output.
- LIBMOUNT_DEBUG=0xffff
- enables debug output.
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).
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