I use VirtualBox for most of my development efforts on my macBook. I recently had to reinstall CentOS7 on this new machine, and was noticing a 10s (2x 5s) delay on startup times for Emacs. Doing an strace -tt on the Emacs binary, I noticed it would timeout on trying to lookup its own hostname. I'm not sure why, but this timesout on the DNS lookups were annoying the hell out of me. The solution was to add the local hostname (set in /etc/hostname) to the 127.0.0.1 entry in /etc/hosts.