When and why would I need to run fsck?

My understanding is that fsck can be used when a files data and meta-data are inconsistent. But I understand that fsck can take a really long time.

What is the harm in losing a little metadata (such as access time and created time) on a few files?

What other problems can be caused by a few inconsitent files?

There is plenty of documentation on how to use fsck, but I am more interested on knowing when and why I should use it.

fsck is like scandisk. It checks that the file system is correct and you have no loose data nodes (lost data). On my servers I run a fsck every 6 months(ish) just to make sure that all is well in the world. I can't remember the last time anything was fixed by it.

My servers at home run 24/7 unless I have a power outage greater than 20 minutes, my ups's are rated for 30 mins but I do like to shut things down nicely, some of my databases can take 5 mins to commit and shut down.

Work wise my servers are customer facing and I have a strict quarterly process to power down and bring each server back up after full backups and cleaning up stuff that shouldn't be their. I have over 100 servers in my estate 90%/10% split *nix and Windoze.

So in short it does a File System Check. Good for checking the file system is good.

You should always ALWAYS make a backup before running fsck. Especially if you run it with -y(not advisable in most cases), it does have a potential to make data irrecoverable depending upon the errors in the filesystem. As with anything, backup before you run a command.

Apart from "creation" time not existing in Linux (it's "change" time): a file ("everything is a file") may be polled by a process waiting to Do Something based on say modification time. Change time is for instance used by the 'dump' utility.


Think of the results as the computer equivalent of amnesia an epilepsy combined. Basically everything that can fail will. On a small level that may just mean you not being able to open your previous OGG, MKV or SVG files, or your smartphone no longer working or on a larger level Gmail or Yahoo mail serving you your emails but partially mixed with somebody elses emails or critical infrastructure failures and I don't mean just the Internet.