I recently made some changes to my /etc/X11/xorg.conf file which backfired and Ubuntu (12.10 in this case) would crash while loading the operating system.

It should be simple enough to undo the last change you made to a system file when booting into recovery mode, but alas it is not straightforward because when booting into recovery mode the filesystem is mounted as read-only! Oh dear!

1. Boot into “Ubuntu (Recovery Mode)”
2. From the recovery menu drop to a root shell.
3. Enter the following command to remount your filesystem as read-write:

1

mount -o remount,rw /

4. Make the required changes to your operating system and then exit/reboot/whatever.