Comment 2 for bug 1953553

Thank you for taking the time to file a bug report.

The following excerpt seems to be the key to explaining what's going on:

ERROR: Unable to start MySQL server:
mysqld: Can't read dir of '/etc/mysql/conf.d/' (OS errno 2 - No such file or directory)
mysqld: [ERROR] Stopped processing the 'includedir' directive in file /etc/mysql/my.cnf at line 20.
mysqld: [ERROR] Fatal error in defaults handling. Program aborted!

It seems like the /etc/mysql/conf.d/ directory has been removed, which in turn makes MySQL to error out when trying to read files from it. I would recommend purging the package and installing it from scratch, but you can try recreating the directory by hand and see if solves the issue. Either way, this is very likely a local configuration issue.

Since it seems likely to me that this is a local configuration problem,
rather than a bug in Ubuntu, I am marking this bug as 'Incomplete'.

However, if you believe that this is really a bug in Ubuntu, then we would
be grateful if you would provide a more complete description of the problem
with steps to reproduce, explain why you believe this is a bug in Ubuntu
rather than a problem specific to your system, and then change the bug
status back to "New".

For local configuration issues, you can find assistance here:
http://www.ubuntu.com/support/community