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URL:
https://askubuntu.com/q/1189127
Title:
Is it possible to schedule `fsck` command and run it in background?
ID:
/2019/11/15/Is-it-possible-to-schedule-_fsck_-command-and-run-it-in-background_
Created:
November 15, 2019
Edited: June 12, 2020
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The Myth - “NO it can’t be done”
All these most popular google search hits ignore the question or say NO it can’t be done. That isn’t true though. fsck is scheduled to run during boot before the filesystem is mounted as rw (read/write). As such most answers says it can’t be run after system is fully booted:
- Can I run fsck or e2fsck when Linux file system is mounted?
- Doing disk checks on mounted OS partition?
- Is it possible to run fsck to only see errors on mounted disk
Why it needs to be done
This is a good question for some types of users.
- Sometimes I can go weeks before rebooting my laptop and will not get the benefit of
fsckregularly. - Other times I can reboot dozens of times an hour as I try out a new grub theme or switch between distributions to compare functionality. In this case I don’t want to wait the extra 30 seconds for
fsckto run. As such I have it disabled during boot.
What the manual says about how it can be done
You can run fsck -n but it won’t accurately report errors for ReiserFS (whatever that filesystem is). There is another obscure file system called it refuses to check altogether.
$ man fsck
FSCK(8) System Administration FSCK(8)
NAME
fsck - check and repair a Linux filesystem
SYNOPSIS
fsck [-lsAVRTMNP] [-r [fd]] [-C [fd]] [-t fstype] [filesystem...] [--] [fs-specific-
options]
DESCRIPTION
fsck is used to check and optionally repair one or more Linux filesystems. filesys can
be a device name (e.g. /dev/hdc1, /dev/sdb2), a mount point (e.g. /, /usr, /home), or
an ext2 label or UUID specifier (e.g. UUID=8868abf6-88c5-4a83-98b8-bfc24057f7bd or
LABEL=root). Normally, the fsck program will try to handle filesystems on different
physical disk drives in parallel to reduce the total amount of time needed to check all
of them.
If no filesystems are specified on the command line, and the -A option is not speci‐
fied, fsck will default to checking filesystems in /etc/fstab serially. This is equiv‐
alent to the -As options.
The exit code returned by fsck is the sum of the following conditions:
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
OPTIONS
-n For some filesystem-specific checkers, the -n option will cause the fs-specific
fsck to avoid attempting to repair any problems, but simply report such problems
to stdout. This is however not true for all filesystem-specific checkers. In
particular, fsck.reiserfs(8) will not report any corruption if given this
option. fsck.minix(8) does not support the -n option at all.
What it looks like checking mounted partitions
I have three partitions; Old (broken) Ubuntu 16.04, Ubuntu 19.04 (called Ubuntu 18.04) and New Ubuntu 16.04. When running fchk they look like this:
$ sudo fsck -n /dev/nvme0n1p7
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
Warning! /dev/nvme0n1p7 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem check.
Old_Ubuntu_16.04 has been mounted 358 times without being checked, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Old_Ubuntu_16.04: 433493/1515520 files (0.8% non-contiguous), 4956946/6061568 blocks
$ sudo fsck -n /dev/nvme0n1p10
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
Warning! /dev/nvme0n1p10 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem check.
Ubuntu_18.04: clean, 719735/1782368 files, 5770105/7129088 blocks
$ sudo fsck -n /dev/nvme0n1p6
fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
Warning! /dev/nvme0n1p6 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem check.
New_Ubuntu_16.04: clean, 833786/2953920 files, 8256858/11829504 blocks
As you can see fsck is telling us Old Ubuntu 16.04 requires a real fsck be run with system mounted in ro (read only mode) so fixes can be applied if necessary. However I already know it is broken.
Later I’ll update this answer with a cron weekly job that runs fsck on three mounted Ubuntu partitions in check only mode.