FSCK (File System Consistency Check) is a command-line utility to check and repair Linux filesystem errors. This makes sure filesystem for integrity and consistency.
fsck is a front-end program and it calls the respective program for the specific filesystem to run. Fsck usually runs after the system fails to boot, the file system becomes corrupted, or the attached drive fails to function properly.
In this tutorial, we will learn about the fsck command and how to repair filesystems on a Linux distribution.
Prerequisites
- Linux or Unix-like system
- A user with root access
When using fsck command
- The system automatically finds system inconsistent usually after a system crash or power loss or after unclean unmount.
- System fails to boot
- When the system has I/O error
- Schedule to run fsck for filesystem intergerity on boot or every few months
fsck command in Linux
The fsck command follows a basic syntax.
$ sudo fsck [Option] [Filesystem]The [Option] in the syntax is the options that are available with the fsck utility (fsck option are given at end of this tutorial). The [Filesystem] can be a device, a partition, a mount point, and so on. If no credential is added to the [Filesystem], fsck checks the devices listed in the fstab file.
fsck is included by default in all Linux distributions. Having a good backup is a safe point to run the fsck command. fsck keeps all the files intact and only checks the integrity of the filesystem. This command can be run manually or automatically.
Before attempting to check or repair filesystems, always remember to unmount the partition. If this is not done, the filesystem may get be damaged.
Check and Repair Filesystem Errors
Fsck is commonly used to repair errors on corrupted ext3 or ext4 filesystems. To use the fsck utility, you must first ensure that the partition has been unmounted. You will get an error and your process will be aborted if you try to run the fsck command on partition without unmounting it. After the process is complete, you can again mount the filesystem.
If you are not sure about the device name, use df command, lsblk, or fdisk (fdisk -l) to find it.
$ sudo df -hUse the unmount command to avoid causing any filesystem damage.
Syntax:
$ sudo umount [filesystem]You can use the -p option along with the fsck utility to automatically repair any problems that can be safely resolved without the user's interference.
Syntax:
$ sudo fsck -p [Filesystem]For Example:
$ sudo umount /dev/sdc
$ sudo fsck -p /dev/sdcOutput:
$ sudo fsck -p /dev/sdc
fsck from util-linux 2.34
exfatfsck 1.3.0
Checking file system on /dev/sdc.
File system version 1.0
Sector size 512 bytes
Cluster size 128 KB
Volume size 55 GB
Used space 4 MB
Available space 55 GB
Totally 1 directories and 3 files.
File system checking finished. No errors found.After the check and repair make sure to mount the disk.
Repair Root File System Error
Because a root machine cannot be unmounted, Fsck cannot check for errors. However, you have you can run fsck in recovery mode.
By rebooting the machine while in Rescue mode, you can run fsck. You can run fsck to repair root system file errors using the following steps.
Enter the boot menu and select "Advanced Options" during the reboot.
Choose “Recovery mode” from the advanced options menu, and then pick “fsck” from the drop-down menu.
A message window will popup, asking if you want your / filesystem remounted. Select the option "Yes".
By selecting the option "Resume," you may now return to normal boot.
fsck Options
There is a list of options that are available with the fsck utility for specific purposes. Some of the useful fsck options are:
1. Perform fsck dry run - This performs a test run.
fsck -N /dev/sdc2. Run non-interactively - answers yes to all questions, this will avoid all prompts
fsck -y /dev/sdc3. Just Print fsck Error to Stdout without repair
fsck -n /dev/sdc4. Run fsck on all filesystems
fsck -ARThe -R will skip the root filesystem as its cant be unmounted on a running machine
5. Run fsck for a specific filesystem
The fsck command is a wrapper and internally uses the respective filesystem checker command (fsck.*). You can find the following various fsck checker commands such as fsck.ext2, fsck.ext3, fsck.ext4, etc.).
# cd /sbin
# ls fsck*
fsck fsck.cramfs fsck.ext2 fsck.ext3 fsck.ext4 fsck.minix fsck.xfsThe following table shows all options of the fsck command.
| Option | Description |
| -A | Check all file systems present in /etc/fstab |
| -C | Display progress bar |
| -f | Check filesystem forcefully |
| -l | Lock the device |
| -M | Do not check mounted filesystems |
| -N | Print output without executing any actions |
| -P | Check multiple filesystems parallelly |
| -p | Automatically repair any issues that can be safely resolved without the need for user interaction |
| -R | Do not check the root filesystem when used with -A |
| -r | Print statistics for each device that has been checked |
| -T | Do not show the Title |
| -t | Specify the filesystem types to be checked (This can be done using man command) |
| -v | Provide a detailed output |
| -y | Assume 'yes' to all the questions |
fstab is a file that directs the operating system on how and where to mount the partitions. You may find a list of entries in the fstab file by opening it with /etc/fstab.
The <pass> option specifies the order in which file system checks are performed during a reboot. If the value is 0 then it does not check. If the value is 1, the file systems are checked one at a time, but if the value is 2, all of the file systems are searched simultaneously. The root file system has a value of 1, and all other file systems you want to check should have a value of 2.
A sample /etc/fstab file:
<filesystem> <mount point> <type> <options> <dump> <pass>
/dev/sda / ext4 errors=remount-ro 0 1
/dev/sdb none swap sw 0 0
/dev/sdc /mnt/data ext4 defaults,noatime,nofail 0 2Conclusion
In this tutorial, we learned how to use the fsck command to check and repair filesystems in Linux. You can refer fsck man pages for a more complete description.