Today, I did a fresh installation of Ubuntu 9.04 inside virtual box. My original idea was to play with sudoers and sudo command. I edited /etc/sudoers and logged out. Next time I tried to sudo , I go some parse error in /etc/sudoers. I was stuck . I needed sudo for modifying the file. But sudo was preventing me because of the error.
Then, I remembered about the recovery mode. Rebooted the machine and I pressed escape to get the standard grub screen as shown below.
Selecting recovery mode showed the following screens. ( The second figure below shows the remaining part of the recovery screen which is hidden from the first screen.)
Later I rebooted again and re-entered the recovery mode again to find out what capabilities it offers.
The recovery screen offers you the following menu entries on ubuntu 9.04 .
a) Try to make free space - this is useful if your machine is stuck for the want of free disk space.
b) Dpkg - If you select this option you can repair broken packages. Very useful ,if the system is stuck after a package installation.
c) fsck - if the system is stuck with file system error you can try this option.
d) grub - You can update the grub boot loader from this option.
e) netroot - Your TCP/IP network settings will be enabled and system will drop to a root shell.
This option is useful if you are trouble shooting network related issues.
f) root- Plain old root shell . Suitable for editing config files.
g) xfix - This option will try to reconfigure your X window system