MySql DB from Ubuntu to RHEL

The simplest option is to just back up everything in the filesystem and carry it over.

To find out where your data is, look at the datadir variable with in mysql

test> show variables like 'datadir';
+---------------+-------------------+
| Variable_name | Value             |
+---------------+-------------------+
| datadir       | /var/lib/mysql/   |
+---------------+-------------------+
1 row in set (0.00 sec)

Note Your actual value may differ.

Then from your shell shut down mysql, back it up and copy it over. Something like:

> sudo service mysql shutdown
> cd /var/lib/mysql
> sudo tar -czf /path/with/enough/space/db.tgz *

Copy your db.tgz over to your new server and uncompress it on your new servers datadir while it is shutdown

I ran into apparmor headaches getting multiple instances going on ubuntu myself. Your configs look legit but I'm not super familiar w/ apparmor to spot a subtle problem if one lied there. In my case I was just running multiple copies of the same binaries w/ different cnfs

Your initial error cited

name="/run/mysqld/mysqld-5-5-20.sock"

It seems maybe there's a config option that didn't come through in what you pasted that's looking to work with /run (instead of /var/run) ?