So you’ve recently made a change to your mysql installation and see the following in

 /var/lib/mysql/server.err

080317 14:08:50 mysqld started
080317 14:08:50 [ERROR] Fatal error: Can't change to run as user 'mysql' ; Please check that the user exists!

080317 14:08:50 [ERROR] Aborting

080317 14:08:50 [Note] /usr/sbin/mysqld: Shutdown complete

080317 14:08:50 mysqld ended

 This is a problem that many a time spent on google has not found the result, so I am writing here what exactly to do in this situation …

 First off

 cd /var/lib/mysql

Now run

ls -la

 No doubt you will see something similar to this:

drwx--x--x   2 27 mysql     4096 Mar 17 14:05 mysql

Notice the “27 mysql”, the user no longer existsing in /etc/passwd.

This is fairly simple to fix.

adduser mysql

chown mysql:mysql -R /var/lib/mysql

Now start up Mysql i.e. “service start mysql” and everyhing should be fine.