Comment 2 for bug 1775021

Thanks for filing this bug in Ubuntu.

I see you installed and purged mysql multiple times in a matter of minutes, coupled with config file changes.

Eventually it failed with error messages like:
2018-06-04T07:22:38.355592Z 0 [Note] /usr/sbin/mysqld: ready for connections.
Version: '5.7.22-0ubuntu18.04.1' socket: '/var/run/mysqld/mysqld.sock' port: 3306 (Ubuntu)
2018-06-04T07:22:44.638691Z 2 [Note] Access denied for user 'root'@'localhost'
2018-06-04T07:28:48.825508Z 3 [Note] Access denied for user 'root'@'localhost'
2018-06-04T07:37:37.691235Z 0 [Note] Giving 0 client threads a chance to die gracefully
2018-06-04T07:37:37.691265Z 0 [Note] Shutting down slave threads
...
2018-06-04T07:37:37.792556Z 0 [Note] InnoDB: Dumping buffer pool(s) to /var/lib/mysql/ib_buffer_pool
2018-06-04T07:37:37.792917Z 0 [ERROR] InnoDB: Cannot open '/var/lib/mysql/ib_buffer_pool.incomplete' for writing: No such file or directory
2018-06-04T07:37:39.542696Z 0 [Note] InnoDB: Shutdown completed; log sequence number 2590304

and

Setting up mysql-server-5.7 (5.7.22-0ubuntu18.04.1) ...
update-alternatives: error: alternative path /etc/mysql/mysql.cnf doesn't exist
dpkg: error processing package mysql-server-5.7 (--configure):
 installed mysql-server-5.7 package post-installation script subprocess returned error exit status 2

It is hard to diagnose this sequence of events.

I suggest you really purge all mysql packages and its config files, and start over. If you can get us a precise sequence of events that lead to an error, then please paste them in this bug.

Thanks