fsck.ext4 (8)

Leading comments

Copyright 1993, 1994, 1995 by Theodore Ts'o.  All Rights Reserved.
This file may be copied under the terms of the GNU Public License.

(The comments found at the beginning of the groff file "man8/fsck.ext4.8".)

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 ] device

DESCRIPTION

e2fsck is used to check the ext2/ext3/ext4 family of file systems. For ext3 and ext4 filesystems 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 filesystems that use journalling, e2fsck will normally replay the journal and exit, unless its superblock indicates that further checking is required.

device is the device file where the filesystem is stored (e.g. /dev/hdc1).

Note that in general it is not safe to run e2fsck on mounted filesystems. 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 filesystem is mounted. If e2fsck asks whether or not you should check a filesystem 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.

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 the backup superblock is dependent on the filesystem's blocksize. For filesystems with 1k blocksizes, a backup superblock can be found at block 8193; for filesystems with 2k blocksizes, at block 16384; and for 4k blocksizes, at block 32768.

Additional backup superblocks can be determined by using the mke2fs program using the -n option to print out where the superblocks were created. The -b option to mke2fs, which specifies blocksize of the filesystem must be specified in order for the superblock locations that are printed out to be accurate.

If an alternative superblock is specified and the filesystem is not opened read-only, e2fsck will make sure that the primary superblock is updated appropriately upon completion of the filesystem 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 filesystem 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 filesystem. This option causes e2fsck to try to optimize all directories, either by reindexing them if the filesystem supports directory indexing, or by sorting and compressing directories for smaller directories, or for filesystems 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 filesystem 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 filesystem. 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 filesystem.

discard

Attempt to discard free blocks and unused inode blocks after the full filesystem check (discarding blocks is useful on solid state devices and sparse / thin-provisioned storage). Note that discard is done in pass 5 AFTER the filesystem 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.

-f

Force checking even if the file system seems clean.

-F

Flush the filesystem 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 filesystem 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 filesystem. Hence, badblocks(8) must be given the blocksize of the filesystem 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 filesystem 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 filesystem 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.

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 filesystem 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 filesystem 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 filesystem, 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.

AUTHOR

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

SEE ALSO

e2fsck.conf(5), badblocks(8), dumpe2fs(8), debugfs(8), e2image(8), mke2fs(8), tune2fs(8)