A nifty little new option that came in OS X 10.9 Mavericks and stays in Yosemite is the ability to delete all of the firmware variables you’ve created. This can get helpful if you’ve got a bunch of things that you’ve done to a system and want to remove them all. If you run nvkram followed by a -p option you’ll see all of the configured firmware variables:
nvram -p
If you run it with a -d you’ll delete the given variables that you define (e.g. boot-args):
nvram -d boot-args
But, if you run the -c you’ll wipe them all:
nvram -c
