A Mac’s Recovery HD is a good solution to reinstall OS X. If your Mac is a Mid 2011 or newer model and you are running OS X 10.7 Lion or 10.8 Mountain Lion you can boot into the recovery system by holding down the option key at boot.
The recovery system which will be booted is very lean and downloads a macOS Image from Apple’s servers, this works for Ethernet and even WiFi connections. The big problem is, Apple did not add an option to set a proxy server! So if you are behind a proxy you won’t be able to use the recovery feature. That’s why I searched for a solution and found an easy one even for guys not that familiar with IT.Read more OS X Lion and Mountain Lion Recovery for Proxy-Users