Comment 2 for bug 630028

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that you're using a non-standard location for your socket. However mysqld apparmor profile (in /etc/apparmor.d/usr.sbin.mysqld) hasn't been updated to allow access to the custom directory.

See https://wiki.ubuntu.com/DebuggingApparmor#Debugging%20procedure for more information on how to update mysqld apparmor profile.