After updating mysql on a server that is running cpanel, Nagios kept reporting that mysql is down. I double checked and the database server was running just fine, so I proceeded with a step by step analysis, the issue proved to be the following:
root@cpanel [~]# /usr/local/nagios/libexec/check_mysql /usr/local/nagios/libexec/check_mysql: error while loading shared libraries: libmysqlclient.so.15: cannot open shared object file: No such file or directory