12.2. File System-Specific Information for fsck

All of these file sytems use the e2fsck binary to perform file system checks and repairs. The file names fsck.ext2, fsck.ext3, and fsck.ext4 are hardlinks to this same binary. These binaries are run automatically at boot time and their behavior differs based on the file system being checked and the state of the file system.

A full file system check and repair is invoked for ext2, which is not a metadata journaling file system, and for ext4 file systems without a journal.

For ext3 and ext4 file systems with metadata journaling, the journal is replayed in userspace and the binary exits. This is the default action as journal replay ensures a consistent file system after a crash.

If these file systems encounter metadata inconsistencies while mounted, they record this fact in the file system superblock. If e2fsck finds that a file system is marked with such an error, e2fsck performs a full check after replaying the journal (if present).

e2fsck may ask for user input during the run if the -p option is not specified. The -p option tells e2fsck to automatically do all repairs that may be done safely. If user intervention is required, e2fsck indicates the unfixed problem in its output and reflect this status in the exit code.

Commonly used e2fsck run-time options include:

All options for e2fsck are specified in the e2fsck(8) manual page.

The following five basic phases are performed by e2fsck while running:

The e2image(8) utility can be used to create a metadata image prior to repair for diagnostic or testing purposes. The -r option should be used for testing purposes in order to create a sparse file of the same size as the file system itself. e2fsck can then operate directly on the resulting file. The -Q option should be specified if the image is to be archived or provided for diagnostic. This creates a more compact file format suitable for transfer.

No repair is performed automatically at boot time. To initiate a file system check or repair, use the xfs_repair tool.

A clean log on a file system is required for xfs_repair to operate. If the file system was not cleanly unmounted, it should be mounted and unmounted prior to using xfs_repair. If the log is corrupt and cannot be replayed, the -L option may be used to zero the log.

It is possible to run xfs_repair in a dry run, check-only mode by using the -n option. No changes will be made to the file system when this option is specified.

xfs_repair takes very few options. Commonly used options include:

All options for xfs_repair are specified in the xfs_repair(8) manual page.

The following eight basic phases are performed by xfs_repair while running:

For more information, see the xfs_repair(8) manual page.

xfs_repair is not interactive. All operations are performed automatically with no input from the user.

If it is desired to create a metadata image prior to repair for diagnostic or testing purposes, the xfs_metadump(8) and xfs_mdrestore(8) utilities may be used.

The btrfsck tool is used to check and repair btrfs file systems. This tool is still in early development and may not detect or repair all types of file system corruption.

By default, btrfsck does not make changes to the file system; that is, it runs check-only mode by default. If repairs are desired the --repair option must be specified.

The following three basic phases are performed by btrfsck while running:

The btrfs-image(8) utility can be used to create a metadata image prior to repair for diagnostic or testing purposes.