CentOS switching to MySQL user
Solution 1:
By default on a CentOS system the mysql account is locked
passwd -S mysql
mysql LK 2012-08-29 0 99999 7 -1 (Password locked.)
If you look at the shadow file entry
mysql:!!:15581::::::
You'll see that there isn't a valid password set. If you want you can always set a password using the passwd command and unlock it using passwd too.