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tune2fs Command in Linux: Syntax, Options & ext4 Tuning Examples

tune2fs reads and changes tunable parameters on unmounted or read-only-safe ext2, ext3, and ext4 block devices — mount counts, check intervals, volume labels, UUIDs, reserved blocks, default mount options, and feature flags stored in the superblock.

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Reviewed byDeepak Prasad

tune2fs Command in Linux: Syntax, Options & ext4 Tuning Examples
About tune2fs reads and changes tunable parameters on unmounted or read-only-safe ext2, ext3, and ext4 block devices — mount counts, check intervals, volume labels, UUIDs, reserved blocks, default mount options, and feature flags stored in the superblock.
Tested on Ubuntu 25.04 (Plucky Puffin); tune2fs 1.47.2 (e2fsprogs 1.47.2-1ubuntu1); kernel 7.0.0-27-generic
Package e2fsprogs (apt/deb) · e2fsprogs (dnf/rpm)
Man page tune2fs(8)
Privilege root / sudo
Distros

Ubuntu, Debian, RHEL, AlmaLinux, Fedora, and other distros shipping e2fsprogs.

For read-only superblock dumps without changing anything, see dumpe2fs.
Related guide

tune2fs — quick reference

Inspect the superblock

Read current tunables from the filesystem superblock. Safe on a mounted root when you only use -l.

When to use Command
List superblock fields (label, UUID, mount counts, features, reserved blocks) sudo tune2fs -l /dev/mapper/ubuntu--vg-ubuntu--lv
Show only the volume label sudo tune2fs -l DEVICE | grep 'volume name'
Show mount-count and check-interval fields sudo tune2fs -l DEVICE | grep -Ei 'mount count|check interval|last checked'

Filesystem check scheduling

Control when e2fsck runs at boot. On modern ext4 with journaling, many sites disable periodic checks and rely on monitoring instead.

When to use Command
Set maximum mounts before forced fsck (-1 disables mount-count checks) sudo tune2fs -c 30 DEVICE
Pick a random max mount count between 20 and 40 sudo tune2fs -c random DEVICE
Disable mount-count-based fsck sudo tune2fs -c -1 DEVICE
Set the recorded mount count (triggers fsck if above -c value) sudo tune2fs -C 5 DEVICE
Set maximum days/weeks/months between checks (2w, 6m, 90d) sudo tune2fs -i 2w DEVICE
Disable time-based fsck (-i 0; -i -1 errors on Ubuntu 25.04) sudo tune2fs -i 0 DEVICE
Stamp last-checked time to now (snapshots / maintenance scripts) sudo tune2fs -T now DEVICE
Set last-checked time explicitly (YYYYMMDD or YYYYMMDDhhmmss) sudo tune2fs -T 202607011200 DEVICE

Labels, mount metadata, and UUID

When to use Command
Set a volume label (max 16 characters on ext4) sudo tune2fs -L mydata DEVICE
Record the last mount point path in the superblock sudo tune2fs -M /mnt/data DEVICE
Assign a specific UUID string sudo tune2fs -U c1b9d5a2-f162-11cf-9ece-0020afc76f16 DEVICE
Generate a new random UUID (device must be unmounted) sudo tune2fs -U random DEVICE
Generate a time-based UUID sudo tune2fs -U time DEVICE
Clear the filesystem UUID sudo tune2fs -U clear DEVICE

Error handling and extended options

When to use Command
Continue after detected errors (default on many systems) sudo tune2fs -e continue DEVICE
Remount read-only when the kernel sees errors sudo tune2fs -e remount-ro DEVICE
Panic the kernel on filesystem errors sudo tune2fs -e panic DEVICE
Flag the filesystem so fsck runs at next mount sudo tune2fs -E force_fsck DEVICE
Set RAID stride width in filesystem blocks sudo tune2fs -E stride=16 DEVICE
Set RAID stripe width in filesystem blocks sudo tune2fs -E stripe_width=32 DEVICE
Force past errors (needed twice when replaying an external journal) sudo tune2fs -f DEVICE

Reserved blocks

Root keeps a pool of blocks for daemons when the disk fills up. Default is often 5% on ext4.

When to use Command
Set reserved space as a percentage sudo tune2fs -m 5 DEVICE
Set an absolute reserved block count sudo tune2fs -r 1000 DEVICE
Set which user may use reserved blocks (name or UID) sudo tune2fs -u root DEVICE
Set which group may use reserved blocks (name or GID) sudo tune2fs -g 0 DEVICE

Default mount options

Store default mount flags in the superblock (honoured by ext4 on 2.6.35+ kernels). Use ^ to clear an option.

When to use Command
Add default mount options sudo tune2fs -o user_xattr,acl DEVICE
Clear a default mount option sudo tune2fs -o ^acl DEVICE

Journaling and features

Destructive on live data — run only on an unmounted device or a disposable test image. Back up first.

When to use Command
Add an ext3 journal to an ext2 filesystem sudo tune2fs -j DEVICE
Override journal size or external journal device sudo tune2fs -J size=128 DEVICE
Enable an ext4 feature (example: dir_index) sudo tune2fs -O dir_index DEVICE
Clear a feature (caret prefix) sudo tune2fs -O ^sparse_super DEVICE
Grow inode size to 256 bytes (requires e2fsck first) sudo tune2fs -I 256 DEVICE

Quota inodes

When to use Command
Enable user quota feature and quota inode sudo tune2fs -Q usrquota DEVICE
Enable group quota inode sudo tune2fs -Q grpquota DEVICE
Enable project quota inode sudo tune2fs -Q prjquota DEVICE
Clear user quota feature sudo tune2fs -Q ^usrquota DEVICE

Undo log

When to use Command
Write block changes to an undo file (restore with e2undo) sudo tune2fs -z /path/to/undo.e2undo DEVICE
Clear undo file setting sudo tune2fs -z "" DEVICE

tune2fs — command syntax

Synopsis from tune2fs usage text on Ubuntu 25.04 (tune2fs 1.47.2):

text 
tune2fs [-c max_mounts_count] [-e errors_behavior] [-f] [-g group]
        [-i interval[d|m|w]] [-j] [-J journal_options] [-l]
        [-m reserved_blocks_percent] [-o [^]mount_options[,...]]
        [-r reserved_blocks_count] [-u user] [-C mount_count]
        [-L volume_label] [-M last_mounted_dir]
        [-O [^]feature[,...]] [-Q quota_options]
        [-E extended-option[,...]] [-T last_check_time] [-U UUID]
        [-I new_inode_size] [-z undo_file] device

device can be /dev/sda1, LABEL=name, or UUID=uuid. Most write operations need the filesystem unmounted; -l is the usual safe read on a mounted volume. Requires sudo.

tune2fs — command examples

Essential List superblock — read-only on a live LVM root

Before changing anything, read the superblock. On Ubuntu 25.04 this works read-only on the mounted root logical volume.

Run the command:

bash 
sudo tune2fs -l /dev/mapper/ubuntu--vg-ubuntu--lv

Sample output (trimmed):

text 
tune2fs 1.47.2 (1-Jan-2025)
Filesystem volume name:   <none>
Last mounted on:          /
Filesystem UUID:          72457fae-1731-4c94-b5c1-ac4564f4311c
Filesystem state:         clean
Errors behavior:          Continue
Mount count:              13
Maximum mount count:      -1
Last checked:             Mon Oct  6 10:35:36 2025
Check interval:           0 (<none>)
Reserved block count:     672747

Check mount-count and interval fields when planning fsck policy:

bash 
sudo tune2fs -l /dev/mapper/ubuntu--vg-ubuntu--lv | grep -Ei 'mount count|check interval|last checked'

Sample output:

text 
Mount count:              13
Maximum mount count:      -1
Last checked:             Mon Oct  6 10:35:36 2025
Check interval:           0 (<none>)

A max mount count of -1 and check interval 0 mean neither mount-count nor time rules force e2fsck at boot.

Common Set a volume label on a loop ext4 test image

Use a loop-backed ext4 image in /tmp for write tests — never leave it mounted after you finish.

Create and attach a test image:

bash 
sudo dd if=/dev/zero of=/tmp/tune2fs-test.img bs=1M count=64 status=none
sudo mkfs.ext4 -F -L origlabel /tmp/tune2fs-test.img
LOOP=$(sudo losetup -f --show /tmp/tune2fs-test.img)

Set a new label:

bash 
sudo tune2fs -L testlabel "$LOOP"

Sample output:

text 
tune2fs 1.47.2 (1-Jan-2025)

Verify and clean up:

bash 
sudo tune2fs -l "$LOOP" | grep 'volume name'
sudo tune2fs -L origlabel "$LOOP"
sudo losetup -d "$LOOP"
sudo rm -f /tmp/tune2fs-test.img

Sample verification line:

text 
Filesystem volume name:   testlabel

Restore the original label and remove the loop device so the host is unchanged.

Common Schedule and disable periodic e2fsck checks

On a test loop device, set mount-count and time limits, then turn them off again.

bash 
sudo tune2fs -c 30 "$LOOP"
sudo tune2fs -C 5 "$LOOP"
sudo tune2fs -i 2w "$LOOP"

Sample output:

text 
tune2fs 1.47.2 (1-Jan-2025)
Setting maximal mount count to 30
Setting current mount count to 5
Setting interval between checks to 1209600 seconds

Confirm:

bash 
sudo tune2fs -l "$LOOP" | grep -E 'Mount count|Maximum mount|Check interval'

Sample output:

text 
Mount count:              5
Maximum mount count:      30
Check interval:           1209600 (2 weeks)

Disable both policies before cleanup:

bash 
sudo tune2fs -c -1 "$LOOP"
sudo tune2fs -i 0 "$LOOP"

On Ubuntu 25.04, tune2fs -i -1 prints interval between checks is too big — use -i 0 instead.

Common Tune reserved block pool for root-only emergency space

Adjust how much space only privileged users can allocate when the disk is nearly full.

bash 
sudo tune2fs -m 5 "$LOOP"
sudo tune2fs -r 1000 "$LOOP"

Sample output:

text 
tune2fs 1.47.2 (1-Jan-2025)
Setting reserved blocks percentage to 5% (819 blocks)
Setting reserved blocks count to 1000

Check the result:

bash 
sudo tune2fs -l "$LOOP" | grep -E 'Reserved block'

Sample output:

text 
Reserved block count:     1000
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
Advanced Rotate UUID on an unmounted test filesystem

UUID changes apply only when the filesystem is not mounted. Use a loop image, not production /.

bash 
sudo tune2fs -U random "$LOOP"

Sample output:

text 
tune2fs 1.47.2 (1-Jan-2025)

Read the new value:

bash 
sudo tune2fs -l "$LOOP" | grep 'Filesystem UUID'

Update /etc/fstab if it references the old UUID before mounting this device on a real system.

Advanced Add a journal to ext2 (offline conversion)

tune2fs -j upgrades ext2 to ext3 by creating a journal inode. Test on a throwaway image first.

bash 
sudo dd if=/dev/zero of=/tmp/tune2fs-ext2.img bs=1M count=64 status=none
sudo mkfs.ext2 -F -q /tmp/tune2fs-ext2.img
LOOP2=$(sudo losetup -f --show /tmp/tune2fs-ext2.img)
sudo tune2fs -j "$LOOP2"

Sample output:

text 
tune2fs 1.47.2 (1-Jan-2025)
Creating journal inode: done

Confirm the feature flag:

bash 
sudo tune2fs -l "$LOOP2" | grep 'Filesystem features'

Sample output:

text 
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype sparse_super large_file

Clean up:

bash 
sudo losetup -d "$LOOP2"
sudo rm -f /tmp/tune2fs-ext2.img

Never run -j or -O feature changes on a mounted production filesystem without a verified backup.

Advanced Mark filesystem for fsck on next mount

-E force_fsck sets the error flag so e2fsck runs at the next mount — useful after snapshot consistency checks.

bash 
sudo tune2fs -E force_fsck "$LOOP"

Sample output:

text 
tune2fs 1.47.2 (1-Jan-2025)
Setting filesystem error flag to force fsck.

State changes from clean to clean with errors until e2fsck clears it:

bash 
sudo tune2fs -l "$LOOP" | grep 'Filesystem state'

Sample output:

text 
Filesystem state:         clean with errors
Advanced Capture an undo log before risky tune2fs writes

Pair -z with e2undo when you need a rollback path. The undo file does not survive power loss.

bash 
sudo tune2fs -z /tmp/tune2fs-undo.e2undo -L ztest "$LOOP"

Sample output:

text 
tune2fs 1.47.2 (1-Jan-2025)
Overwriting existing filesystem; this can be undone using the command:
    e2undo /tmp/tune2fs-undo.e2undo /dev/loopN

List the undo file, then remove it during cleanup:

bash 
ls -la /tmp/tune2fs-undo.e2undo
sudo rm -f /tmp/tune2fs-undo.e2undo

tune2fs — when to use / when not

Choose tune2fs when you need to read or change ext-family superblock tunables. Use another tool when the task is formatting, repair, or non-ext filesystems.

Use tune2fs when Use something else when
  • You need to read label, UUID, mount counts, or feature flags on ext2/ext3/ext4 (-l)
  • You want to adjust fsck scheduling, reserved blocks, or default mount options on an ext filesystem
  • You are converting ext2 to ext3 with -j or enabling ext4 features with -O on an unmounted device
  • You are scripting LVM snapshot checks and need to stamp -T now after a clean e2fsck
  • You are creating a new ext filesystem from scratch → mke2fs
  • You only need a superblock dump without changes → dumpe2fs
  • The filesystem has errors or needs repair → e2fsck in rescue mode
  • The filesystem is XFS, Btrfs, or NTFS → xfs_admin, btrfs, or ntfs tools — not tune2fs
  • You need to resize the filesystem or LV → extend LVM and resize tools after backup

tune2fs vs dumpe2fs

Both read superblock data; only tune2fs writes tunables.

tune2fs dumpe2fs
Primary role Read and change tunable parameters Dump superblock and block-group metadata
Writes superblock Yes (most flags except -l) No
Best for Labels, UUID, fsck policy, reserved blocks Deep inspection, debugging layout
Mounted root -l is usually safe read-only Read-only dump

See the dumpe2fs command when you need more detail than tune2fs -l provides.

Filesystem creation, inspection, and repair around ext volumes.

Command One line
tune2fs Tune ext superblock parameters (this page)
mount Mount by UUID, LABEL, or device path

Browse the full index in our Linux commands reference.

tune2fs — interview corner

What does tune2fs do on Linux?

tune2fs adjusts tunable parameters stored in the superblock of ext2, ext3, and ext4 filesystems. It does not format disks — mke2fs does that — and it is not a full repair tool like e2fsck.

Common tasks:

  • Read metadata with tune2fs -l DEVICE (label, UUID, mount counts, features)
  • Set volume labels (-L), UUIDs (-U), and fsck schedules (-c, -i, -T)
  • Change reserved block pools (-m, -r) and default mount options (-o)
  • Enable features such as journals (-j) or ext4 flags (-O) on an unmounted device

Most writes need root and an unmounted filesystem; -l on a mounted ext4 root is the everyday safe read.

A strong answer is:

"tune2fs reads and changes ext superblock tunables — labels, UUIDs, fsck scheduling, reserved blocks, and feature flags. I use tune2fs -l for inspection and only run write flags on unmounted filesystems or test images."

How do you disable periodic e2fsck on ext4?

Two superblock counters drive automatic checks:

Field Disable with
Maximum mount count sudo tune2fs -c -1 DEVICE
Check interval (time) sudo tune2fs -i 0 DEVICE

Verify:

bash 
sudo tune2fs -l DEVICE | grep -Ei 'maximum mount|check interval'

Sample lines when disabled:

text 
Maximum mount count:      -1
Check interval:           0 (<none>)

On Ubuntu 25.04, tune2fs -i -1 fails — use -i 0. Journaled ext4 systems often disable both counters and rely on monitoring plus manual e2fsck after unclean shutdown.

A strong answer is:

"I set maximal mount count to -1 with tune2fs -c -1 and disable the time interval with tune2fs -i 0, then confirm with tune2fs -l. On Ubuntu I avoid -i -1 because it errors on e2fsprogs 1.47.2."

When can you change a filesystem UUID with tune2fs?

The filesystem must be unmounted. Changing the UUID of a mounted volume corrupts in-flight metadata.

bash 
sudo tune2fs -U random /dev/sdXN

Accepted -U values: a hex UUID string, random, time, or clear.

After a change, update /etc/fstab, systemd mount units, and LVM references that used the old UUID. blkid shows the current value.

A strong answer is:

"UUID changes require an unmounted ext filesystem. I use tune2fs -U random or a explicit UUID, then update fstab and verify with blkid before mounting."

What is the difference between tune2fs and dumpe2fs?

tune2fs is for reading (-l) and writing tunable superblock fields. dumpe2fs dumps richer layout detail — block groups, bitmaps, inode tables — and never modifies the disk.

Use tune2fs -l for a quick admin summary (label, counts, features). Use dumpe2fs when debugging allocation or comparing block-group layout.

A strong answer is:

"tune2fs -l is the quick tunables view and can change settings; dumpe2fs is a read-only deep dump of superblock and block groups for forensic or layout analysis."

Why does ext4 reserve blocks for root?

By default ext4 reserves about 5% of blocks so root (and sometimes a reserved group) can still write when the disk is full — syslog, package managers, and rescue shells keep working.

tune2fs -m sets the percentage; tune2fs -r sets an absolute block count. On large data volumes admins sometimes lower the percentage; on small root volumes keeping reserve space is safer.

A strong answer is:

"Reserved blocks let root write when the filesystem is full so the system stays manageable. tune2fs -m changes the percentage; I lower it only on dedicated data volumes after checking operational impact."

Troubleshooting

Symptom Likely cause Fix
Couldn't find valid filesystem superblock Wrong device, wiped disk, or non-ext FS Confirm type with blkid or file -s DEVICE; use the correct tool for XFS/Btrfs
Filesystem is mounted / busy device Write attempted on mounted FS Unmount, or use -l only for reads on live systems
interval between checks is too big with -i -1 e2fsprogs 1.47.2 rejects -1 for interval Use sudo tune2fs -i 0 DEVICE to disable time-based checks
Could not find program / permission errors Missing sudo Prefix with sudo or run as root
UUID already in use Duplicate UUID on another volume Pick a unique UUID with -U random and update fstab
Feature change requests e2fsck -O, -j, or -I altered metadata layout Run sudo e2fsck -f DEVICE before mounting
tune2fs: invalid option Typo or wrong e2fsprogs build Compare with usage text from tune2fs (invalid flag prints synopsis on 1.47.2)
Rohan Timalsina

is a technical writer and Linux enthusiast who writes practical guides on Linux commands and system administration. He focuses on simplifying complex topics through clear explanations.

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