Cause: Due to junk characters in 'my.cnf', MySQL service could not get started.
Upon checking we have noticed following error logs InnoDB at/var/log/mysql.
InnoDB: Error: trying to add tablespace 325 of name './database_name/core_session.ibd'
InnoDB: to the tablespace memory cache, but tablespaceInnoDB: 325 of name './databasename/phpfox_pages_perm.ibd' already exists in the tablespaceInnoDB: memory cache!
Step-1: Login into the server via SSH with root user and take the backup of all databases for safe side. /var/lib/mysql
mkdir -p /data/database/backup/ (you can set your desired path to store the database backup)
cp -R /var/lib/mysql/* /data/database/backup/
Step-2: We moved out the corrupt database from the Mysql directory (/var/lib/mysql)
The issue should be fixed after performing the above steps. But in this particular case we found another issue.
Issue-2: Again Mysql service could not get started.
Step-1: Login into server via SSH with root user. We have checked the logs at /var/log/mysql and found as follow.
150525 05:23:00 mysqld_safe mysqld from pid file /var/lib/mysql/servername.domain.com.pid ended
150525 5:23:00 [Note] /usr/sbin/mysqld: Shutdown complete
150525 5:22:59 [ERROR] /usr/sbin/mysqld: unknown option
150525 05:22:58 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
150525 05:17:58 mysqld_safe mysqld from pid file /var/lib/mysql/servername.domain.com .pid ended
150525 5:17:58 [Note] /usr/sbin/mysqld: Shutdown complete
150525 5:17:57 [ERROR] /usr/sbin/mysqld: unknown option
Step-2: We went to /etc/my.cnf or /etc/mysql to check the my.cnf file and fire the command as mentioned below.
root@myserver:/etc/mysql$ vi my.cnf
And we have detected the junk characters in 'my.cnf' file. We removed the junk characters, save the my.cnf file and started the Mysql service. The issue was fixed.
root@myserver [/etc]# service mysql start
Starting MySQL.. SUCCESS!
root@myserver [/etc]# service mysql status
SUCCESS! MySQL running (3205)
Note :: MySQL log path may be different according to MySQL server version and operating system.