Force disk checking during boot in Ubuntu

In order to force disk checking during boot in Ubuntu and other modern
operating systems, the 'fsck.mode=force' kernel parameter needs to be
added before booting.

In Ubuntu this is done as follows:
1) At the GRUB screen, press 'e' to edit the kernel parameters.
2) Add 'fsck.mode=force' at the end of the line that starts with the
keyword 'linux'.
3) Press 'Ctrl+x' or 'F10' to boot with the updated kernel parameters.

Note that only the partitions that have '1' or '2' as the fsck option in
'/etc/fstab' will be checked. The value '1' is reserved for the boot
partition, and all the other partitions to be checked should use the
value '2'.