jfs_fscklog

jfs_fscklog [ -c ] [ -d ] [ -p ] [ -V ] device

device
    Specifies the JFS device (e.g., /dev/sda1) to operate on. This is a mandatory argument.

-c
    Clears the JFS fsck log. This action should be performed with caution, as it removes diagnostic information that might be needed for post-mortem analysis.

-d
    Dumps and displays the contents of the JFS fsck log to standard output. This is the default action if no other options are specified, providing details like the last check time and file system state.

-p
    Checks if there are any pending log entries that indicate an incomplete journal replay operation. This is useful to determine if the file system was unmounted cleanly and whether a replay is still required.

-V
    Displays the version information for the jfs_fscklog utility, including the JFS utilities package version.

The jfs_fscklog command is a utility specifically designed for the Journaled File System (JFS). It allows administrators to inspect, clear, or check the status of the file system check (fsck) log stored within the JFS superblock of a given device. This log records crucial information about the last time jfs_fsck was run on the file system, including the outcome, timestamp, and whether any journal replays were performed due to an unclean shutdown.

This utility is invaluable for diagnosing issues after a system crash or improper shutdown, as it provides insights into the integrity of the file system and whether it has been properly checked and repaired. While JFS is less commonly used than some other modern file systems like ext4 or XFS, jfs_fscklog remains an essential tool for managing JFS volumes.

This command is exclusively for JFS file systems; attempting to use it on other file system types will result in an error. It typically requires root privileges (or equivalent) to access and modify raw block devices. Clearing the fsck log (using -c) removes valuable diagnostic history, so it should only be done when you are certain the file system is clean and no longer need the log information for troubleshooting.

When the fsck log is dumped (using the -d option), the output typically includes details such as the timestamp of the last jfs_fsck run, the file system's state (e.g., clean, dirty), and indicators for whether a journal replay was initiated or completed. This information is crucial for understanding the history of the file system's integrity and recovery operations following unexpected shutdowns.

Common usage scenarios for jfs_fscklog include: after a system crash, to verify if jfs_fsck ran and what its outcome was; before mounting a JFS file system in read-write mode, to confirm its cleanliness; or as part of a routine maintenance check to monitor file system health and ensure proper shutdown procedures are followed.

The Journaled File System (JFS) was originally developed by IBM for their AIX operating system in the late 1990s, focusing on high performance and quick recovery. It was subsequently ported to Linux, becoming an officially supported file system within the kernel. jfs_fscklog is an integral part of the standard JFS utilities package for Linux, designed to complement jfs_fsck by providing a direct interface to the file system's internal health records, reinforcing JFS's emphasis on data integrity and rapid post-crash recovery.

jfs_fsck(8), fsck(8), jfs_mkfs(8), mount(8)