I seem to have horribly broken MySQL on our Ubuntu 14.04 LTS server. We recently installed the mysql-proxy package(we've been trying to set up master-master replication, but we've abandoned that for Tungsten), and I suspect that was what did the damage, although removing that package still does not bring the server back to life.
Starting MySQL results in the following output in our logs:
150421 16:44:56 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
150421 16:44:56 [Note] Plugin 'FEDERATED' is disabled.
150421 16:44:56 [Note] Plugin 'InnoDB' is disabled.
150421 16:44:56 [ERROR] Unknown/unsupported storage engine: InnoDB
150421 16:44:56 [ERROR] Aborting
150421 16:44:56 [Note] /usr/sbin/mysqld: Shutdown complete
150421 16:44:56 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
And yes, I've tried the trick of removing /var/lib/mysql/ib_logfile0 and /var/lib/mysql/ib_logfile1 and restarting. MySQL just complains that these files don't exist, and that we need to re-create them.
I found the solution to this problem. I needed to completely uninstall MySQL, its databases, and configuration, and restore from backups. This was accomplished with:
apt-get remove mysql-client-5.5 mysql-client-core-5.5 mysql-common mysql-proxy mysql-server-5.5 mysql-server-core-5.5
and
apt-get purge mysql-client-5.5 mysql-client-core-5.5 mysql-common mysql-proxy mysql-server-5.5 mysql-server-core-5.5
and then reinstalling mysql-server.
It was an extreme solution, but MySQL was extremely broken.