If you are running Ganglia in a non multicast environment, it may be the case where a gmond process occupies 100% of the system’s CPU. In such cases it is helpful to check whether the node should be deaf or not (when it is a node that should not receive any messages from others). So try to set in your gmond.conf:
deaf = yes
and see what happens. This has happened to me on CentOS 6.x systems.
Managing organized complexity 
It also happened to me on Ubuntu
The instructions on DigitalOcean say to “Comment out the whole udp_recv_channel section with the /* … */ syntax, as this server won’t be receiving anything.” However, if you do this (on gmond 3.6.0) it produces lots of “apr_pollset_poll returned unexpected status 22 = Invalid argument” warnings. As above, you must also set “deaf = yes” to fix this.