Ubuntu Manpage: e2fsck - check a Linux ext2/ext3/ext4 file system

Provided by: e2fsprogs_1.47.0-2.4~exp1ubuntu4.1_amd64

NAME

       e2fsck - check a Linux ext2/ext3/ext4 file system

SYNOPSIS

       e2fsck  [  -pacnyrdfkvtDFV  ] [ -b superblock ] [ -B blocksize ] [ -l|-L bad_blocks_file ] [ -C fd ] [ -j
       external-journal ] [ -E extended_options ] [ -z undo_file ] device

DESCRIPTION

e2fsck is used to check the ext2/ext3/ext4 family of file systems. For ext3 and ext4 file systems that
use a journal, if the system has been shut down uncleanly without any errors, normally, after replaying
the committed transactions in the journal, the file system should be marked as clean. Hence, for file
systems that use journaling, e2fsck will normally replay the journal and exit, unless its superblock
indicates that further checking is required.

device is a block device (e.g., /dev/sdc1) or file containing the file system.

Note that in general it is not safe to run e2fsck on mounted file systems. The only exception is if the
-n option is specified, and -c, -l, or -L options are not specified. However, even if it is safe to do
so, the results printed by e2fsck are not valid if the file system is mounted. If e2fsck asks whether
or not you should check a file system which is mounted, the only correct answer is ``no''. Only experts
who really know what they are doing should consider answering this question in any other way.

If e2fsck is run in interactive mode (meaning that none of -y, -n, or -p are specified), the program will
ask the user to fix each problem found in the file system. A response of 'y' will fix the error; 'n'
will leave the error unfixed; and 'a' will fix the problem and all subsequent problems; pressing Enter
will proceed with the default response, which is printed before the question mark. Pressing Control-C
terminates e2fsck immediately.

OPTIONS

-a This option does the same thing as the -p option. It is provided for backwards compatibility
only; it is suggested that people use -p option whenever possible.

-b superblock
Instead of using the normal superblock, use an alternative superblock specified by superblock.
This option is normally used when the primary superblock has been corrupted. The location of
backup superblocks is dependent on the file system's blocksize, the number of blocks per group,
and features such as sparse_super.

Additional backup superblocks can be determined by using the mke2fs program using the -n option to
print out where the superblocks exist, supposing mke2fs is supplied with arguments that are
consistent with the file system's layout (e.g. blocksize, blocks per group, sparse_super, etc.).

If an alternative superblock is specified and the file system is not opened read-only, e2fsck will
make sure that the primary superblock is updated appropriately upon completion of the file system
check.

-B blocksize
Normally, e2fsck will search for the superblock at various different block sizes in an attempt to
find the appropriate block size. This search can be fooled in some cases. This option forces
e2fsck to only try locating the superblock at a particular blocksize. If the superblock is not
found, e2fsck will terminate with a fatal error.

-c This option causes e2fsck to use badblocks(8) program to do a read-only scan of the device in
order to find any bad blocks. If any bad blocks are found, they are added to the bad block inode
to prevent them from being allocated to a file or directory. If this option is specified twice,
then the bad block scan will be done using a non-destructive read-write test.

-C fd This option causes e2fsck to write completion information to the specified file descriptor so that
the progress of the file system check can be monitored. This option is typically used by programs
which are running e2fsck. If the file descriptor number is negative, then absolute value of the
file descriptor will be used, and the progress information will be suppressed initially. It can
later be enabled by sending the e2fsck process a SIGUSR1 signal. If the file descriptor specified
is 0, e2fsck will print a completion bar as it goes about its business. This requires that e2fsck
is running on a video console or terminal.

-d Print debugging output (useless unless you are debugging e2fsck).

-D Optimize directories in file system. This option causes e2fsck to try to optimize all
directories, either by re-indexing them if the file system supports directory indexing, or by
sorting and compressing directories for smaller directories, or for file systems using traditional
linear directories.

Even without the -D option, e2fsck may sometimes optimize a few directories --- for example, if
directory indexing is enabled and a directory is not indexed and would benefit from being indexed,
or if the index structures are corrupted and need to be rebuilt. The -D option forces all
directories in the file system to be optimized. This can sometimes make them a little smaller and
slightly faster to search, but in practice, you should rarely need to use this option.

The -D option will detect directory entries with duplicate names in a single directory, which
e2fsck normally does not enforce for performance reasons.

-E extended_options
Set e2fsck extended options. Extended options are comma separated, and may take an argument using
the equals ('=') sign. The following options are supported:

ea_ver=extended_attribute_version
Set the version of the extended attribute blocks which e2fsck will require while
checking the file system. The version number may be 1 or 2. The default extended
attribute version format is 2.

journal_only
Only replay the journal if required, but do not perform any further checks or repairs.

fragcheck
During pass 1, print a detailed report of any discontiguous blocks for files in the
file system.

discard
Attempt to discard free blocks and unused inode blocks after the full file system
check (discarding blocks is useful on solid state devices and sparse / thin-
provisioned storage). Note that discard is done in pass 5 AFTER the file system has
been fully checked and only if it does not contain recognizable errors. However there
might be cases where e2fsck does not fully recognize a problem and hence in this case
this option may prevent you from further manual data recovery.

nodiscard
Do not attempt to discard free blocks and unused inode blocks. This option is exactly
the opposite of discard option. This is set as default.

no_optimize_extents
Do not offer to optimize the extent tree by eliminating unnecessary width or depth.
This can also be enabled in the options section of /etc/e2fsck.conf.

optimize_extents
Offer to optimize the extent tree by eliminating unnecessary width or depth. This is
the default unless otherwise specified in /etc/e2fsck.conf.

inode_count_fullmap
Trade off using memory for speed when checking a file system with a large number of
hard-linked files. The amount of memory required is proportional to the number of
inodes in the file system. For large file systems, this can be gigabytes of memory.
(For example, a 40TB file system with 2.8 billion inodes will consume an additional
5.7 GB memory if this optimization is enabled.) This optimization can also be enabled
in the options section of /etc/e2fsck.conf.

no_inode_count_fullmap
Disable the inode_count_fullmap optimization. This is the default unless otherwise
specified in /etc/e2fsck.conf.

readahead_kb
Use this many KiB of memory to pre-fetch metadata in the hopes of reducing e2fsck
runtime. By default, this is set to the size of two block groups' inode tables
(typically 4MiB on a regular ext4 file system); if this amount is more than 1/50th of
total physical memory, readahead is disabled. Set this to zero to disable readahead
entirely.

bmap2extent
Convert block-mapped files to extent-mapped files.

fixes_only
Only fix damaged metadata; do not optimize htree directories or compress extent trees.
This option is incompatible with the -D and -E bmap2extent options.

check_encoding
Force verification of encoded filenames in case-insensitive directories. This is the
default mode if the file system has the strict flag enabled.

unshare_blocks
If the file system has shared blocks, with the shared blocks read-only feature
enabled, then this will unshare all shared blocks and unset the read-only feature bit.
If there is not enough free space then the operation will fail. If the file system
does not have the read-only feature bit, but has shared blocks anyway, then this
option will have no effect. Note when using this option, if there is no free space to
clone blocks, there is no prompt to delete files and instead the operation will fail.

Note that unshare_blocks implies the "-f" option to ensure that all passes are run.
Additionally, if "-n" is also specified, e2fsck will simulate trying to allocate
enough space to deduplicate. If this fails, the exit code will be non-zero.

-f Force checking even if the file system seems clean.

-F Flush the file system device's buffer caches before beginning. Only really useful for doing
e2fsck time trials.

-j external-journal
Set the pathname where the external-journal for this file system can be found.

-k When combined with the -c option, any existing bad blocks in the bad blocks list are preserved,
and any new bad blocks found by running badblocks(8) will be added to the existing bad blocks
list.

-l filename
Add the block numbers listed in the file specified by filename to the list of bad blocks. The
format of this file is the same as the one generated by the badblocks(8) program. Note that the
block numbers are based on the blocksize of the file system. Hence, badblocks(8) must be given
the blocksize of the file system in order to obtain correct results. As a result, it is much
simpler and safer to use the -c option to e2fsck, since it will assure that the correct parameters
are passed to the badblocks program.

-L filename
Set the bad blocks list to be the list of blocks specified by filename. (This option is the same
as the -l option, except the bad blocks list is cleared before the blocks listed in the file are
added to the bad blocks list.)

-n Open the file system read-only, and assume an answer of `no' to all questions. Allows e2fsck to
be used non-interactively. This option may not be specified at the same time as the -p or -y
options.

-p Automatically repair ("preen") the file system. This option will cause e2fsck to automatically
fix any file system problems that can be safely fixed without human intervention. If e2fsck
discovers a problem which may require the system administrator to take additional corrective
action, e2fsck will print a description of the problem and then exit with the value 4 logically
or'ed into the exit code. (See the EXIT CODE section.) This option is normally used by the
system's boot scripts. It may not be specified at the same time as the -n or -y options.

-r This option does nothing at all; it is provided only for backwards compatibility.

-t Print timing statistics for e2fsck. If this option is used twice, additional timing statistics
are printed on a pass by pass basis.

-v Verbose mode.

-V Print version information and exit.

-y Assume an answer of `yes' to all questions; allows e2fsck to be used non-interactively. This
option may not be specified at the same time as the -n or -p options.

-z undo_file
Before overwriting a file system block, write the old contents of the block to an undo file. This
undo file can be used with e2undo(8) to restore the old contents of the file system should
something go wrong. If the empty string is passed as the undo_file argument, the undo file will
be written to a file named e2fsck-device.e2undo in the directory specified via the
E2FSPROGS_UNDO_DIR environment variable.

WARNING: The undo file cannot be used to recover from a power or system crash.

EXIT CODE

       The exit code returned by e2fsck is the sum of the following conditions:
            0    - No errors
            1    - File system errors corrected
            2    - File system errors corrected, system should
                   be rebooted
            4    - File system errors left uncorrected
            8    - Operational error
            16   - Usage or syntax error
            32   - E2fsck canceled by user request
            128  - Shared library error

SIGNALS

       The following signals have the following effect when sent to e2fsck.

       SIGUSR1
              This signal causes e2fsck to start displaying a completion bar or emitting  progress  information.
              (See discussion of the -C option.)

       SIGUSR2
              This signal causes e2fsck to stop displaying a completion bar or emitting progress information.

REPORTING BUGS

Almost any piece of software will have bugs. If you manage to find a file system which causes e2fsck to
crash, or which e2fsck is unable to repair, please report it to the author.

Please include as much information as possible in your bug report. Ideally, include a complete
transcript of the e2fsck run, so I can see exactly what error messages are displayed. (Make sure the
messages printed by e2fsck are in English; if your system has been configured so that e2fsck's messages
have been translated into another language, please set the the LC_ALL environment variable to C so that
the transcript of e2fsck's output will be useful to me.) If you have a writable file system where the
transcript can be stored, the script(1) program is a handy way to save the output of e2fsck to a file.

It is also useful to send the output of dumpe2fs(8). If a specific inode or inodes seems to be giving
e2fsck trouble, try running the debugfs(8) command and send the output of the stat(1u) command run on the
relevant inode(s). If the inode is a directory, the debugfs dump command will allow you to extract the
contents of the directory inode, which can sent to me after being first run through uuencode(1). The
most useful data you can send to help reproduce the bug is a compressed raw image dump of the file
system, generated using e2image(8). See the e2image(8) man page for more details.

Always include the full version string which e2fsck displays when it is run, so I know which version you
are running.

ENVIRONMENT

       E2FSCK_CONFIG
              Determines the location of the configuration file (see e2fsck.conf(5)).

AUTHOR

       This version of e2fsck was written by Theodore Ts'o <tytso@mit.edu>.