A word of warning…
If you use FileVault 2 (full disk encryption) on your Mac, you might be tempted at some point to perform a Safe Boot by setting the boot flag:
sudo nvram boot-args="-x"
Don’t!
What will actually happen is that the Mac will enter an endless cycle of rebooting every time you enter your password to unlock the disk.
If you have done this, then the way to get out of it is to reset your PRAM like this:
Do a reboot, and immediately hit ⌥ ⌘ P R together (Option + Command + P + R), and hold them down until the Mac reboots again. Now it should boot up normally.
If you need to perform a Safe Boot, Apple say that you should disable FileVault 2 first. (I have not tried this.)
Thanks! I had set the boot-args on my MacBook Pro and entered the boot loop. Luckily the guest login was available to find your post (although it took a bit of Google-fu). Resetting the PRAM took care of it and you saved me a call to Apple.
Awesome!
Could you please post here the search terms that you tried first when you encountered the problem? That way, other people who have the same problem stand a better chance of finding this page!
Thanks.