RTFM · Troubleshooting
Filesystem problems
Reading what the kernel thinks happened to your disks: mount failures, corruption symptoms, and safe recovery sequencing.
What the kernel saw
lsblk -f # topology + filesystem + UUID map
dmesg | grep -iE 'ext4|xfs|i/o error' | tail -30
findmnt # currently mounted treeRefuses to mount at boot
fstab entries are validated at boot; a typo in UUID or filesystem type cascades into emergency shell.
# Find truth
blkid /dev/sdb1
# Compare against
grep -v '^#' /etc/fstabMount unfamiliar corrupted volumes read-only until diagnosed: the ro option protects evidence from well-meant journal replays.
Space disappearing invisibly
Deleted-but-open files hold space until the last reader closes: df says full, du disagrees.
lsof +L1 # deleted still-open files
# Restart the holding process to reclaim spaceProve it works: clean unmount cycle
target filesystem mounts read-write, accepts writes, unmounts without complaint, remounts identically.
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