If you have setup munin-node on a cPanel server it's possible that your MySQL graphs stop updating at sometime, or don't even generate from the beginning.
To fix, edit the following file:
And make sure that the mysql section contains the following:
[mysql*] user root group wheel env.mysqladmin /usr/bin/mysqladmin env.mysqlopts --defaults-extra-file=/root/.my.cnf
Finally, don't forget to restart munin-node