jfs_fsck

jfs_fsck [ -f ] [ -V ] device

device
    The special file (e.g., /dev/hda1, /dev/sdb2) corresponding to the device or partition containing the JFS filesystem.

-f
    Forces the filesystem check even if the filesystem is marked as clean.

-V
    Enables verbose output, showing more details about the checking process.

jfs_fsck is the utility used to check and optionally repair a Journaled File System (JFS). JFS is a 64-bit journaled file system developed by IBM, originally for AIX and later ported to OS/2 and Linux. Like other fsck utilities, jfs_fsck examines the consistency of a JFS filesystem's metadata. If inconsistencies are found, it attempts to correct them to restore the filesystem to a usable state.

This process is crucial for recovering data integrity after system crashes, power failures, or other events that might lead to an unclean filesystem shutdown. It's imperative that the filesystem being checked is not mounted during the operation to prevent further corruption or data loss. The utility reads the filesystem's journal and applies any uncommitted transactions to ensure a consistent state before performing a full metadata check.

The JFS filesystem must be unmounted before running jfs_fsck. Running it on a mounted filesystem can lead to severe data corruption and potential data loss.

While jfs_fsck attempts to repair inconsistencies, there is always a risk of data loss, especially when significant corruption exists. Backups are highly recommended before attempting a repair on a critical filesystem.

Checking large filesystems can be time-consuming, during which the filesystem will be inaccessible. Typically, jfs_fsck requires root privileges to operate on block devices.

jfs_fsck returns different exit codes depending on the outcome of the operation:

• 0: No errors were found.
• 1: Filesystem errors were corrected.
• 2: Filesystem errors were found but not corrected.
• 4: An operation error occurred (e.g., cannot open device).
• 8: A usage error occurred (e.g., invalid arguments).

This command is typically used after an unclean system shutdown (e.g., power loss) when the system detects that a JFS filesystem was not properly unmounted. It can also be run periodically for preventative maintenance, although the journaling feature significantly reduces the frequency required for manual checks. In many Linux distributions, jfs_fsck might be automatically invoked by the generic fsck utility during boot if the filesystem's check count or last check time exceeds a configured threshold, or if the filesystem was not cleanly unmounted.

JFS, the Journaled File System, was originally developed by IBM for its AIX Unix operating system in the early 1990s. It was later ported to OS/2 as JFS2. The Linux kernel gained JFS support in 2001, primarily driven by IBM's contributions to the open-source community. jfs_fsck is part of the jfsutils package, which provides the necessary user-space tools to manage JFS filesystems on Linux. While JFS is not as widely adopted as Ext4 or XFS on Linux, it remains a stable and reliable option. The development of jfs_fsck and the entire jfsutils suite ensures the maintainability and integrity of JFS volumes on Linux.

fsck(8), fsck.jfs(8), mount(8), umount(8), jfs_mkfs(8), jfs_tune(8)