For many reason Mysql service may go down. If the mysql service is showing down, first you check the mysql log file ‘/var/log/mysqld.log’ for errors. If you get the following errors in log, you can easily fix this by correcting the access permission of mysql (/var/lib/mysql where the ibdata1 is located) directory to mysql user access permission.
101114 12:45:43 mysqld started
101114 12:45:43 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: ‘open’.
InnoDB: Cannot continue operation.
101114 12:45:43 mysqld ended
You can correct the permission by running the following command and finally restart the mysql service.
chown -R mysql:mysql /var/lib/mysql