10. Filesystem Repair
Sometimes our filesystem isn't always in the best condition, if we have a sudden shutdown, our data can become corrupt. It's up to the system to try to get us back in a working state (although we sure can try ourselves).
The fsck (filesystem check) command is used to check the consistency of a filesystem and can even try to repair it for us. Usually when you boot up a disk, fsck will run before your disk is mounted to make sure everything is ok. Sometimes though, your disk is so bad that you'll need to manually do this. However, be sure to do this while you are in a rescue disk or somewhere where you can access your filesystem without it being mounted.
$ sudo fsck /dev/sda
Look at the manpage for fsck to see what else it can do.
What command is used to check the integrity of a filesystem?