It looks like your MySQL server process is hitting a problem when
it tries to change its user id to that of the user 'mysql'.

There are two possible reasons for this:

1. You're starting the server process as a user who isn't 'root',
   so the user doesn't have the necessary privilege to change
   the UID of the server process.

 -- OR --

2. You *are* starting the server process as 'root', but your
   system doesn't have a user called 'mysql', so the process
   is trying, and failing, change its UID to a user that
   doesn't exist.

Try "finger mysql" to see whether you actually have a user named
'mysql'.

Thinking about it, there are other possibilities, assuming that
you *do* have a user named 'mysql'.

3. The 'mysql' user doesn't have a home directory, or for some
   reason that user doesn't have write-access to its home directory.

4. The 'mysql' user doesn't have the necessary access privileges
   to /opt/mysql and all of its sub-directories.

However, my money is on reason 2.

David Harper
Cambridge, England