Saturday, December 13, 2008


The nvram utility is used to view and set Open Firmware NVRAM variables. Open Firmware, (aka non-volatile RAM), controls system boot options. To change a variable, you must run nvram as root.

Viewing Open Firmware variables

There are about 50 Open Firmware variables. To view all variables, use:
nvram -p

Setting Open Firmware variables

You must be root to set a variable. To set a variable, assign a value with an equals sign:
nvram scroll-lock=false

After setting a variable, they are saved during the next clean restart or shutdown.

To set multiple variables at once, list them in a text file in variable=value format, one per line.
Then, feed them all to nvram with:
nvram -f text-file

You can also create new variables by simply assigning a value to a new variable name. It won't have any meaning to the system unless some application reads it, but it is a nice option.

Deleting Open Fireware variables

To delete a variable, use:
nvram -d variable