Fixing Innodb Registered as a storage Engine Failed

So you have a nice wordpress (or similar site) running, but then all of a sudden you got a nasty message telling you that, the InnobDB registration as a storage engine failed.

# tail /var/log/mariadb/mariadb.log
InnoDB: If that is the case, please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.5/en/error-creating-innodb.html
160914  6:45:29 [ERROR] Plugin 'InnoDB' init function returned error.
160914  6:45:29 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
160914  6:45:29 [ERROR] Failed to initialize plugins.
160914  6:45:29 [ERROR] Aborting
160914  6:45:29 [Note] /usr/libexec/mysqld: Shutdown complete

160914 06:45:29 mysqld_safe mysqld from pid file /var/lib/mysql/wpstack.localdomain.pid ended

# systemctl status mariadb
● mariadb.service - MariaDB database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; enabled; vendor preset: disabled)
  Drop-In: /etc/systemd/system/mariadb.service.d
           └─limits.conf
   Active: failed (Result: exit-code) since Wed 2016-09-14 06:25:38 UTC; 2min 32s ago
  Process: 1434 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=1/FAILURE)
  Process: 1433 ExecStart=/usr/bin/mysqld_safe --basedir=/usr (code=exited, status=0/SUCCESS)
  Process: 1305 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=0/SUCCESS)
 Main PID: 1433 (code=exited, status=0/SUCCESS)

Sep 14 06:25:35 wpstack.localdomain systemd[1]: Starting MariaDB database se....
Sep 14 06:25:37 wpstack.localdomain mysqld_safe[1433]: 160914 06:25:37 mysqld...
Sep 14 06:25:37 wpstack.localdomain mysqld_safe[1433]: 160914 06:25:37 mysqld...
Sep 14 06:25:38 wpstack.localdomain systemd[1]: mariadb.service: control pro...1
Sep 14 06:25:38 wpstack.localdomain systemd[1]: Failed to start MariaDB data....
Sep 14 06:25:38 wpstack.localdomain systemd[1]: Unit mariadb.service entered....
Sep 14 06:25:38 wpstack.localdomain systemd[1]: mariadb.service failed.
Hint: Some lines were ellipsized, use -l to show in full.
[root@wpstack ~]# systemctl start mariadb
Job for mariadb.service failed because the control process exited with error code. See "systemctl status mariadb.service" and "journalctl -xe" for details.
[root@wpstack ~]# systemctl start mariadb
Job for mariadb.service failed because the control process exited with error code. See "systemctl status mariadb.service" and "journalctl -xe" for details.

This is naturally a problem since until it is resolved you have no database service running. It is fairly easy to resolve in most cases, by removing the log from var/lib/mysql

mv /var/lib/mysql/ib_logfile0{,.bak}  	   	 	   
mv /var/lib/mysql/ib_logfile1{,.bak}  	   	 	   
mv /var/lib/mysql/ibdata1{,.bak} 

These simply move the files away, which allows InnoDB to continue operating. Please note that this may not always fix your issue and in some situations might result in data loss, so it is advisable to take a backup of the database filesystem before proceeding.