Rackspace Ubuntu 12.04 apache2 causing Out of memory
Solution 1:
/usr/bin/host running for 7 hours at 36% CPU is weird on its own, but because you're also running a Wordpress website I am comfortable saying that you probably have an outdated plugin and your server is compromised.
My suggestion is to contact Rackspace support and have them either identify the problem (If it's not malware) or format / reload if it is. Once you have a fresh install be sure that your application, and application plugins are up to date.