Comment 6 for bug 383087

I found what was not correct :

my /etc/apparmor.d/usr.sbin.mysqld was not correctly set up with the location I use for mysql (/home/mysql)

Tow lines:

/var/lib/mysql/ r,
/var/lib/mysql/** rwk,

should be replaced by:

/home/mysql/ r,
/home/mysql/** rwk,

It is well described in
http://case.oncle-tom.net/2008/05/04/modifier-emplacement-donnees-serveur-mysql/

Thanks.
Maybe it can help others.