FSCK

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FSCK (File System Consistency Check)

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What does FSCK do?

fsck (file system consistency check) is a system utility used to check and repair filesystems. FSCK is made up of various tools that are made to handle different filesystem types, these are stored within /usr/sbin:

lrwxrwxrwx 1 root root         8 Mar 23  2022 dosfsck -> fsck.fat
-rwxr-xr-x 1 root root    360280 Jun  1  2022 e2fsck
-rwxr-xr-x 1 root root     43440 Apr  9 15:32 fsck
-rwxr-xr-x 1 root root      1185 Feb 24  2022 fsck.btrfs
-rwxr-xr-x 1 root root     31168 Apr  9 15:32 fsck.cramfs
lrwxrwxrwx 1 root root         6 Jun  1  2022 fsck.ext2 -> e2fsck
lrwxrwxrwx 1 root root         6 Jun  1  2022 fsck.ext3 -> e2fsck
lrwxrwxrwx 1 root root         6 Jun  1  2022 fsck.ext4 -> e2fsck
-rwxr-xr-x 1 root root     84360 Mar 23  2022 fsck.fat
-rwxr-xr-x 1 root root     55712 Apr  9 15:32 fsck.minix
lrwxrwxrwx 1 root root         8 Mar 23  2022 fsck.msdos -> fsck.fat
lrwxrwxrwx 1 root root         8 Mar 23  2022 fsck.vfat -> fsck.fat
-rwxr-xr-x 1 root root      1968 Feb  9  2022 fsck.xfs
-rwxr-xr-x 1 root root     51592 Nov  1  2022 ntfsclone
-rwxr-xr-x 1 root root     35200 Nov  1  2022 ntfscp

Purpose of fsck

Checking Filesystem Integrity: It scans the filesystem for inconsistencies and potential errors, such as corrupted metadata, lost clusters, and bad sectors.
Repairing Errors: fsck can fix detected issues to prevent data loss and improve system stability.

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You can only run a filesystem check on an unmounted disk.

Scanning a specific disk (optional repair):

fsck -t ext4 /dev/sda2

Scanning all disks (optional repair)

fsck -A

FSCK Options:

-A	Check all filesystems.
-t [option]	Specify filesystem type
-y	Automatically attempt to fix any errors without user prompt
-n	Do not attempt to repair
-f	Forces a check, even if the filesystem appears to be fine
-T	Skip mounted filesystems
-R	Skip the root filesystem

Boot the server into 'single user mode'

B. Once in single user mode, we can look to initiate the fsck

We will first need to check the filesystem type being used:

get the device name:

root@test:~# df
Filesystem                        1K-blocks    Used Available Use% Mounted on
tmpfs                                400556    1068    399488   1% /run
/dev/mapper/ubuntu--vg-ubuntu--lv  15371208 7497096   7071504  52% /
tmpfs                               2002776       0   2002776   0% /dev/shm
tmpfs                                  5120       0      5120   0% /run/lock
/dev/sda2                           1992552  256828   1614484  14% /boot
tmpfs                                400552       4    400548   1% /run/user/0

In this example, we want to check '/dev/mapper/ubuntu--vg-ubuntu--lv' which is mounted to /.

Check the filesystem type:

root@test:~# blkid /dev/mapper/ubuntu--vg-ubuntu--lv
/dev/mapper/ubuntu--vg-ubuntu--lv: UUID="2f1c5c3e-54e0-4edc-9d19-a1f170959479" BLOCK_SIZE="4096" TYPE="ext4"

As you can see, in this example the type is ext4.

C. Running the fsck:

The general command structure for running an fsck is as below:

##Check for errors (No repair)
fsck.filesystem_type /dev/device_name -o ro

##Check and repair errors
fsck.filesystem_type /dev/device_name

In this example, I'm going to run a check and then a repair seperately:

##Check for errors (No repair)
fsck.ext4 /dev/mapper/ubuntu--vg-ubuntu--lv -o ro

##Check and repair errors
fsck.ext4 /dev/mapper/ubuntu--vg-ubuntu--lv