jfs_logdump

jfs_logdump [-m] [-h] device

-m
    Dump the entire log, including padding areas

-h
    Print usage information and exit

The jfs_logdump command is a diagnostic utility for the Journaled File System (JFS), used to extract and display the contents of the JFS transaction log (journal) from a block device in a human-readable format. JFS logs record filesystem metadata transactions to enable crash recovery and maintain integrity. This tool translates binary log structures into text, revealing details like log headers, transaction blocks, page types, and redo/undo records.

Primarily for debugging, it helps analyze log recovery processes, verify log integrity before running jfs_fsck, or investigate filesystem corruption. It supports both inline logs (within the filesystem) and external logs. Output includes timestamps, log sequence numbers (LSN), transaction IDs, and data pages.

Run as root on unmounted devices to avoid interference. Without options, it dumps active log content; use -m for full log including padding. Essential for JFS admins on Linux systems supporting this enterprise filesystem from IBM AIX heritage.

Requires read access to the raw block device; filesystem must be unmounted to prevent inconsistencies. Not for production use during operation.

Shows log header with magic numbers, sequence counts, then transaction blocks with LSN, flags, page types (e.g., dat, map), and hex dumps of data.

Part of jfsutils package from IBM's Linux JFS port (circa 2001); maintains compatibility with original AIX JFS tools for log analysis.

jfs_fsck(8), jfs_debugfs(8), jfs_tune(8)