Comment 15 for bug 1455773

Can't be sure, but I think its a general problem. If you want to try and reproduce it try:

* Start with 14.04 with mysql server installed, configured, and running.
* /etc/apparmor.d should contain a profile file usr.sbin.mysqld
* Do the upgrade first to 14.10 and then to 15.04
* When doing the upgrades you will be asked if you want to supply a password for mysql server. Just say continue
(motivation, you are not trying to change mysqld password)
* check /etc/apparmor.d. If it has the old usr.sbin.mysqld (and an uninstalled dist file) you have hit the "bug"

The old apparmor (5.5) profile cannot work with the updated (5.6) mysqld.