Unless you specifically set one, your root account probably does not have a password - the assumption being that you would log in as someone else and use sudo
.
The guest account probably cannot use sudo
, as that would be all sorts of badness.
Can you download and boot from the System Rescue CD (http://www.sysresccd.org/)?
Before you boot, do df /
to work out which partition your root file system is on. e.g.
$ df /
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 192114204 101260032 81088596 56% /
tells me I need to remember /dev/sda1.
I am assuming for the moment you are not using logical volumes as that adds a few steps in the next bit.
Now boot from the system rescue CD - this will (eventually) take you to a root prompt.
Now mount the root file system:
# mount /dev/sda1 /mnt
There are two ways to go here...
Simple - edit /mnt/etc/shadow, and remove root's password, change:
root:!:15842:0:99999:7:::
to
root::15842:0:99999:7:::
(note the missing !
)
After this you should be able to reboot to Ubuntu and log in as root without a password (remember to set a root password after you log in!).
Complicated - If that does not work - then go back to system rescue and remount your root partition. Then try these commands:
# chroot /mnt
# passwd root
That should change the root password. Reboot, and log in as root.