linuxexpert-practice-labs/labs/lpic-1/104-2-filesystem-integrity/README.md

LPIC-1 104.2: Keeping filesystems healthy

Running out of inodes, checking ext4 with e2fsck, backup superblocks, tune2fs, checking XFS, and space held by deleted files.

Before you start

The lab adds two empty spare disks: /dev/loop40 (100 MiB) and /dev/loop41 (512 MiB). Write answers to the files in /root/lab-answers/.

Tasks

1. Make a 100 MiB ext4 filesystem with few inodes and 1 KiB blocks on /dev/loop40 (mkfs.ext4 -N 1000 -b 1024), mount it, and create empty files in a loop until it fails. Compare df -h and df -i. (With the 4 KiB blocks Ubuntu picks, a filesystem this small has a single block group and no backup superblock for task 3.)
2. Unmount it and run e2fsck, then e2fsck -f, and read the five passes.
3. Find the backup superblocks with dumpe2fs, then run e2fsck -f -b BACKUP /dev/loop40 with the first one. Expect it to report something "FIXED" and "FILE SYSTEM WAS MODIFIED" even on a healthy filesystem: it rewrites the main superblock from the backup. Write the block number of the first backup superblock to /root/lab-answers/3.
4. Change the filesystem's label to scratch and its reserved percentage to 2 with tune2fs, and check both with tune2fs -l.
5. Make an XFS filesystem on /dev/loop41, run xfs_repair -n on it unmounted, then mount it and run xfs_info.
6. Delete a large file while tail -f holds it open, and compare df and du before and after stopping tail. Check it yourself: df gets the space back only when tail ends.

Hints

• for i in $(seq 2000); do touch /mnt/small/f$i || break; done; df -i.
• umount; plain e2fsck skips a clean filesystem, -f forces it.
• dumpe2fs /dev/loop40 | grep -i superblock.
• tune2fs -L, tune2fs -m, tune2fs -l | grep -Ei 'volume name|reserved block|block count'.
• mkfs.xfs, xfs_repair -n, xfs_info MOUNTPOINT.
• lsof +L1 lists deleted files that are still open.