MariaDB-Galera安装之后MariaDb启动不了

[loveniki]

两台机器都安装了MariaDB-Galera，数据也能同步成功；但是关闭之后，下一次Mariadb启动不了了，错误如下：
40225 16:48:48 InnoDB: highest supported file format is Barracuda.

140225 16:48:48 InnoDB: Waiting for the background threads to start

140225 16:48:49 Percona XtraDB (http://www.percona.com) 5.5.35-MariaDB-33.0 started; log sequence number
1602338

140225 16:48:50 [Note] Plugin 'FEEDBACK' is disabled.

140225 16:48:50 [ERROR] mysqld: Can't find file: './mysql/plugin.frm' (errno: 13)

140225 16:48:50 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.

140225 16:48:50 [Note] Server socket created on IP: '0.0.0.0'.

140225 16:48:50 [ERROR] Can't start server : Bind on unix socket: Permission denied

140225 16:48:50 [ERROR] Do you already have another mysqld server running on socket: /var/lib/mysql/mysql.sock ?

140225 16:48:50 [ERROR] Aborting

网上说是权限的问题，哪位高手给个详细的解决方案啊