This is an interesting one: I regularly forget the mysql password for my server. It is one of the most irritating feelings especially when I'm ready to use it and develop some server-side component of my project.
I came across this: https://help.ubuntu.com/community/MysqlPasswordReset
The link gives you a step-by-step to resetting your mysql database's root user password in case you forgot it and all you need is the root/admin account on the box to stop the mysql daemon and restart it in a "no-privilege-check" mode.
In light of this working for me, it dawned on me that when I do CTF competitions, we easily get access to the root/admin user on another team's server. Being able to change their password and dump (or destroy) their database might be a useful trick to know.
In other words, I'm just putting this here and one day it'll be put to use in a competition or for my personal use again -- let's face it: If at this stage, I keep forgetting the password, I'll keep forgetting it. Best to remember how to reset it.
In case the link dies:
How can I reset my MySQL password?
sudo /etc/init.d/mysql stop sudo /etc/init.d/mysql start