Interrupt the grub boot process (by pressing Esc)
select the "Recovery mode" boot item
From the recovery menu select:
root Drop to root shell prompt
To set a password for the root account, type:
and enter a password.
Check the sudoers file, type:
If sudo is installed, you should see the following file:
# This file MUST be edited with the 'visudo' command as root.
# See the man page for details on how to write a sudoers file.
# Uncomment to allow members of group sudo to not need a password
# %sudo ALL=NOPASSWD: ALL
# Host alias specification
# User alias specification
# Cmnd alias specification
# User privilege specification
root ALL=(ALL) ALL
# Members of the admin group may gain root priviliges
%admin ALL=(ALL) ALL
press [esc] : q
to exit vi