e2fsck refuses to check /dev/sdb1, reporting that the superblock is corrupt or has a bad magic number. You know a backup superblock sits at block 32768. Which command restarts the check from that copy?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard hard
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The options
Correct e2fsck -b 32768 /dev/sdb1
Correct. -b names an alternative superblock to use instead of the primary one. When e2fsck completes, it writes the recovered information back over the primary superblock.
Not correct e2fsck -B 32768 /dev/sdb1
Wrong. Lowercase and uppercase differ here: -B tells e2fsck what block size to assume while it searches for a superblock, so this would be read as an absurd 32768-byte block size.
Not correct mke2fs -n /dev/sdb1
Wrong as a repair, though useful beside it. -n makes mke2fs print the layout it would create, including where the backup superblocks would land, without touching the device. It tells you which number to feed to e2fsck -b; it fixes nothing.
Not correct tune2fs -s 1 /dev/sdb1
Wrong. -s toggles the sparse_super feature, which governs how many backup superblocks a filesystem keeps. Changing a feature flag on a filesystem whose superblock is already unreadable helps nothing.
Why
ext2/3/4 keeps redundant copies of the superblock spread through the filesystem precisely so that a damaged primary is survivable. `e2fsck -b <block>` checks using one of those copies and then rewrites the primary. The backup locations depend on block size — commonly 8193 for 1 KiB blocks and 32768 for 4 KiB blocks — and the reliable way to list them for a specific device is `mke2fs -n` or `dumpe2fs` rather than memory.
Where this comes from
- Cited
- manual page e2fsck(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 104 and space the ones you get wrong.
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