nvram [ -p] [-f filename] [ name ] [= value ] ...
Modifies Open Firmware variables, which control the boot-time
behavior of your Macintosh. To list all Open Firmware variables, use
nvram -p. The Apple Open Firmware page is
To change a variable, you must run
nvram as root
or as the superuser. To set a variable, use
variable=value. For example, to configure Mac OS
X to boot verbosely, use
boot-args=-v. (Booting into Mac OS 9 or earlier
will reset this.) The following table lists Open Firmware variables.
Some variables use the Open Firmware Device Tree notation (see the
technotes available at the Apple Open Firmware page).
Be careful changing the
nvram utility, since
incorrect settings can turn a G4 iMac into a $2000 doorstop. If you
render your computer unbootable, you can reset Open Firmware by
zapping the PRAM. To zap the PRAM, hold down Option-
-P-R as you start the computer, and then release the keys when you hear a second startup chime. (If your two hands are busy holding down the other buttons and you have trouble reaching the power button, remember that you can press it with your nose.)
Read the variables to be set from filename, a text file of name=value statements.
Display all Open Firmware variables.
The automatic boot settings. If