New to Percona - need help starting server

140624 15:08:00 [ERROR] /usr/sbin/mysqld: Can’t find file: ‘./mysql/host.frm’ (errno: 13)
140624 15:08:00 [ERROR] Fatal error: Can’t open and lock privilege tables: Can’t find file: ‘./mysql/host.frm’ (errno: 13)

Error 13 means “Permission denied” Check if those two files exist and if they are owned by mysql user and group.

If you moved from 5.6 to 5.5, then that’s a downgrade. Check this link please:

[url]http://dev.mysql.com/doc/refman/5.6/en/downgrading-to-previous-series.html[/url]