I was also able to get it to start by manually adding these lines to the apparmor profile in /etc/apparmor.d/usr.sbin.mysqld:
/run/mysqld/mysqld.pid w, /run/mysqld/mysqld.sock w,
There are already lines for /var/run/mysqld, but it appears that apparmor is not following the symlink that was put there during the precise upgrade.
I was also able to get it to start by manually adding these lines to the apparmor profile in /etc/apparmor. d/usr.sbin. mysqld:
/run/ mysqld/ mysqld. pid w, mysqld/ mysqld. sock w,
/run/
There are already lines for /var/run/mysqld, but it appears that apparmor is not following the symlink that was put there during the precise upgrade.