How to use fsck - Quick Answer

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What is fsck?

fsck, short for file system consistency check, is a utility that examines the file system for errors and attempts to repair them if possible. It uses a combination of built-in tools to check the disk and generates a report of its findings.

On some systems, fsck runs automatically after an unclean shutdown or after a certain number of reboots.

When to Use fsck

Use fsck to check your file system if your system fails to boot, if files on a specific disk become corrupt, or if an attached drive does not act as expected. Unmount the disks you intend to work on before attempting to check or repair them.

Unmount the target disk first. You risk corrupting your file system and losing data if you run fsck on an active disk.

How to Check for Errors on a Disk

Run fsck on the target disk, using the desired options. This example checks all file systems (-A) on /dev/sdb:

fsck -A /dev/sdb

fsck Options and Arguments

Option Action
-A Check all disks listed in /etc/fstab.
-M Skip mounted file systems.
-N Test run. Describes what would happen without executing the check itself.
-P Use with the -A option to run multiple checks in parallel.
-R If using the -A option, do not check the root filesystem.
-t Check only a specific type of filesystem.
-y Interactive repair mode.

Understand fsck Error Codes

The error codes that fsck returns can be understood with the following table from

Code Error Code Meaning
0 No errors
1 Filesystem errors corrected
2 System should be rebooted
4 Filesystem errors left uncorrected
8 Operational error
16 Usage or syntax error
32 Checking canceled by user request
128 Shared-library error

Use fsck to Repair File System Errors

Use the -r option to use the interactive repair option.

This example uses fsck to check all file systems except the root, and will attempt repair using the interactive feature:

fsck -AR -y

To check and attempt to repair any errors on /dev/sdb, use this format:

fsck -y /dev/sdb

What if fsck got interrupted?

If fsck gets interrupted, it will complete any checks in process, but will not attempt to repair any errors it finds.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

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This guide is published under a CC BY-ND 4.0 license.