title: Nagios / MySQL error
body: <p>Ireceived a downtime alert from Nagios that mysql was down on a host. I logged in to the host and found the following error in the mysql error.log file. What are the proper steps to troubleshoot this?</p>
  
  <pre><code>root@ubuntu:/var/log# tail -f mysql/error.log
  101202 11:09:21 [ERROR] Can't open the mysql.plugin table. Please run 
                          mysql_upgrade to create it.
  101202 11:09:21  InnoDB: Started; log sequence number 0 44233
  101202 11:09:21 [ERROR] /usr/sbin/mysqld: Can't find file: './mysql/host.frm' 
                          (errno: 13)
  101202 11:09:21 [ERROR] Fatal error: Can't open and lock privilege tables: 
                          Can't find file: './mysql/host.frm' (errno: 13)
  101202 11:09:51 [Note] Plugin 'FEDERATED' is disabled.
                         /usr/sbin/mysqld: Can't find file: './mysql/plugin.frm' 
                         (errno: 13)
  101202 11:09:51 [ERROR] Can't open the mysql.plugin table. Please run 
                          mysql_upgrade to create it.
  101202 11:09:52  InnoDB: Started; log sequence number 0 44233
  101202 11:09:52 [ERROR] /usr/sbin/mysqld: Can't find file: './mysql/host.frm' 
                          (errno: 13)
  101202 11:09:52 [ERROR] Fatal error: Can't open and lock privilege tables: 
                          Can't find file: './mysql/host.frm' (errno: 13)
  101202 11:10:22 [Note] Plugin 'FEDERATED' is disabled.
                         /usr/sbin/mysqld: Can't find file: './mysql/plugin.frm' 
                         (errno: 13)
  101202 11:10:22 [ERROR] Can't open the mysql.plugin table. Please run 
                          mysql_upgrade to create it.
  101202 11:10:22  InnoDB: Started; log sequence number 0 44233
  101202 11:10:22 [ERROR] /usr/sbin/mysqld: Can't find file: './mysql/host.frm' 
                          (errno: 13)
  101202 11:10:22 [ERROR] Fatal error: Can't open and lock privilege tables: 
                          Can't find file: './mysql/host.frm' (errno: 13)
  </code></pre>