Topic: filesystem
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Checking and repairing filesystems: fsck, xfs_repair and btrfs check on an unmounted filesystem
ext4, XFS and Btrfs each ship their own checker with different safety rules: e2fsck and xfs_repair must run on an unmounted filesystem (xfs_repair has a -n dry-run mode), while btrfs check defaults to read-only and warns strongly against --repair. Exit codes and dry-run output, not intuition, decide whether a repair is needed.
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Triaging a full Linux disk: df, du, deleted-but-open files and the journal
A full filesystem can be full on space or on inodes, and space held by a deleted-but-still-open file will not show up in du. This methodology walks the checks in order — df -h, df -i, du -x, lsof +L1, and journald vacuuming — before anything is deleted.
Machine-readable: JSON