Password Authentication failure

[Bumpalot]

kubuntu 12.10
Have not changed my password, & used this many times, but today it fails to
work!
bumpy@bumpyputer:~$ su
Password:
su: Authentication failure
Any ideas as to why?

[james147]

Try sudo -i instead.

su uses the root password which is not set by default sudo uses your user password and is recommended on ubuntu based systems.

[Bumpalot]

Thanks, that did it!