If your system bas been powered down unexpectedly without being shutdown it is probably a good idea to check the file systems, but if you try to check a mounted file system if you do you almost certainly damage it. Since you can’t unmount the root files system this makes checking it difficult.
Normally the system automatically checks all the file systems when the system boots depending on the number of reboots, days, or times the file system has been mounted since the last check. To force the system to check the root file system the next time the system boots you need to create an empty file in the root directory using ‘touch’. To do this we need to be running as root.
$ su Password:
$ sudo -i Password:
Then we just need to create an empty file in the root folder called ‘forcefsck’.
# touch /forcefsck
The next time the system boots it will check the file system before it is mounted and delete the 'forcefsck' file.