I was getting the following error when trying to change the data directory in ubuntu server 10.04.
100809 19:33:00 [Note] Plugin 'FEDERATED' is disabled. /usr/sbin/mysqld: Can't find file: './mysql/plugin.frm' (errno: 13) 100809 19:33:00 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it. 100809 19:33:00 InnoDB: Operating system error number 13 in a file operation. InnoDB: The error means mysqld does not have the access rights to InnoDB: the directory. InnoDB: File name ./ibdata1 InnoDB: File operation call: 'create'. InnoDB: Cannot continue operation.