Reset Ubuntu root password

So today I forgot the root password to an Ubuntu VM I was playing with recently.  Did the normal thing [1] and hit escape at the grub boot screen and dropped to a root shell followed by the command to reset the password on the account..

passwd <account name>

and was greeted with:

passwd: Authentication token manipulation error
passwd: password unchanged

So with a bit of help from google [2] it turns out the drive just needs to be mounted read/write:

mount -rw -o remount /

before running the passwd command as before.

References

[1] http://www.howtogeek.com/howto/linux/reset-your-forgotten-ubuntu-password-in-2-minutes-or-less/
[2] http://askubuntu.com/questions/91188/authentication-token-manipulation-error