How to Boot into Recovery HD Partition on a Mac OS X with Yosemite, Mavericks, & Mountain Lion
All Macs with OS X Mavericks, Yosemite, Lion, Mountain Lion, have a bootable Recovery partition that can be accessed in case of system problems, allowing you to troubleshoot, restore from Time Machine backups, and even reinstall Mac OS X. There are two ways to reach Recovery mode on a Mac:
Hold down the OPTION key during boot and choose the “Recovery” option, or Hold down Command+R keys during boot to access the Recovery HD partition. Which method you will want to use depends on your Mac model, but the OPTION trick works on every Mac.
You’ll know you’re in recovery mode because the standard desktop won’t be displayed, replaced with a limited Mac OS X Utilities window and a simple Mac OS X menu bar. Here you can use Disk Utility, Time Machine, and restore the OS.
From the Utilities menu you can access Network Utility, use the Firmware Password Utility, and launch the Terminal, which lets you repair user home permissions, launch other apps, and perform other diagnostic tests.
To reinstall OS X from the Recovery partition on a Mac, you will need an active internet connection, that’s because the recovery drive will download the remainder of the OS from Apple. However, the internet aspect is not necessary if you booted with a full Lion USB installer (or Mountain Lion, or Mavericks installers) rather than the built-in Recovery HD partition, or if you used a disk made with the Lion Recovery Assistant tool (again, or 10.8 and 10.9 recovery assistants).
Note that if you deleted the Recovery HD partition, you can not access these features.
Thanks for the tip idea @oldrobots