dumpe2fs Command in Linux: Syntax, Options & Practical Examples

-h prints superblock information only — no per-block-group listing. This is the usual starting point for UUID, block size, and feature checks.

Run the command on the root ext4 device (read-only while / is mounted):

sudo dumpe2fs -h /dev/mapper/ubuntu--vg-ubuntu--lv

Sample output (trimmed):

dumpe2fs 1.47.2 (1-Jan-2025)
Filesystem volume name:   <none>
Last mounted on:          /
Filesystem UUID:          72457fae-1731-4c94-b5c1-ac4564f4311c
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index orphan_file filetype needs_recovery extent 64bit flex_bg metadata_csum_seed sparse_super large_file huge_file dir_nlink extra_isize metadata_csum orphan_present
Filesystem state:         clean
Inode count:              3833856
Block count:              15312896
Block size:               4096
Mount count:              15
Maximum mount count:      -1

Compare UUID here with /etc/fstab and lsblk -f when a volume fails to mount.

Scripts and fstab entries often need the UUID line without the full dump.

Run the command:

sudo dumpe2fs -h /dev/mapper/ubuntu--vg-ubuntu--lv | grep UUID

Sample output:

Filesystem UUID:          72457fae-1731-4c94-b5c1-ac4564f4311c

Cross-check with sudo blkid /dev/mapper/ubuntu--vg-ubuntu--lv — both should agree when the superblock is healthy.

ext4 keeps spare superblocks for recovery. The full dump lists each backup by block number — save these before running fsck -b.

Run the command:

sudo dumpe2fs /dev/mapper/ubuntu--vg-ubuntu--lv | grep -i 'Backup superblock' | head -5

Sample output:

Backup superblock at 32768, Group descriptors at 32769-32776
  Backup superblock at 98304, Group descriptors at 98305-98312
  Backup superblock at 163840, Group descriptors at 163841-163848
  Backup superblock at 229376, Group descriptors at 229377-229384
  Backup superblock at 294912, Group descriptors at 294913-294920

If the primary superblock is corrupt, fsck.ext4 -b 32768 /dev/sdXN tries a backup — only on an unmounted filesystem and after backups exist.

Capacity planning and inode exhaustion checks start with these three fields.

Run the command:

sudo dumpe2fs -h /dev/mapper/ubuntu--vg-ubuntu--lv | grep -E 'Inode count|Block count|Block size|Free blocks|Free inodes'

Inode exhaustion can fill a disk before blocks do; the df and du explains df -i and when IUse% hits 100%.

Sample output:

Inode count:              3833856
Block count:              15312896
Free blocks:              9990711
Free inodes:              3525529
Block size:               4096

Pair with df -h and df -i on the mount point for live usage; dumpe2fs shows filesystem-level totals from the superblock.

Useful when tuning automatic fsck thresholds with tune2fs or explaining why a check ran at boot.

Run the command:

sudo dumpe2fs -h /dev/mapper/ubuntu--vg-ubuntu--lv | grep -E 'Mount count|Maximum mount count|Last mount time|Last write time|Last checked'

Sample output:

Last mount time:          Wed Jul  1 17:34:26 2026
Last write time:          Wed Jul  1 17:23:54 2026
Mount count:              15
Maximum mount count:      -1
Last checked:             Mon Oct  6 10:35:36 2025

-1 for maximum mount count means no forced check based on mount count alone.

The features line shows which ext4 capabilities were enabled at format time — journal, extents, metadata checksums, and similar flags.

Run the command:

sudo dumpe2fs -h /dev/mapper/ubuntu--vg-ubuntu--lv | grep -i features

Sample output:

Filesystem features:      has_journal ext_attr resize_inode dir_index orphan_file filetype needs_recovery extent 64bit flex_bg metadata_csum_seed sparse_super large_file huge_file dir_nlink extra_isize metadata_csum orphan_present
Journal features:         journal_incompat_revoke

If migration or downgrade is on the table, compare this list with target kernel and e2fsprogs support before attempting changes.

-b prints blocks the filesystem has marked bad. No output usually means none are recorded.

Run the command on a small lab image (safe to create and destroy in /tmp):

IMG=/tmp/dumpe2fs-lab.img
dd if=/dev/zero of="$IMG" bs=1M count=32 status=none
mkfs.ext4 -F "$IMG" >/dev/null
dumpe2fs -b "$IMG"
rm -f "$IMG"

Sample output when no bad blocks exist:

dumpe2fs 1.47.2 (1-Jan-2025)

Only the version line appears — no bad block list follows.

When the primary superblock is damaged, -o superblock= reads a copy at a known block — use a number from the Backup superblock lines.

Run the command (read-only on live ext4):

sudo dumpe2fs -o superblock=32768 /dev/mapper/ubuntu--vg-ubuntu--lv | head -10

Sample output:

dumpe2fs 1.47.2 (1-Jan-2025)
Filesystem volume name:   <none>
Last mounted on:          /
Filesystem UUID:          72457fae-1731-4c94-b5c1-ac4564f4311c
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index orphan_file filetype needs_recovery extent 64bit flex_bg metadata_csum_seed sparse_super large_file huge_file dir_nlink extra_isize metadata_csum orphan_present
Filesystem flags:         signed_directory_hash 
Default mount options:    user_xattr acl
Filesystem state:         clean

Matching UUID across primary and backup superblocks confirms you found a valid copy before pointing fsck.ext4 -b at it.

dumpe2fs only understands ext2/ext3/ext4. Pointing it at EFI, swap, or XFS returns a superblock error.

Run the command on an EFI partition (replace device if yours differs):

sudo dumpe2fs /dev/sda1 2>&1 | head -3
sudo blkid /dev/sda1

Sample output:

dumpe2fs 1.47.2 (1-Jan-2025)
dumpe2fs: Bad magic number in super-block while trying to open /dev/sda1
Couldn't find valid filesystem superblock.
/dev/sda1: PARTUUID="5218f62f-744d-4128-95f6-97ddea625886"

Use lsblk -f to pick the correct ext partition before calling dumpe2fs.