Many users are aware of some boot commands for Mac OS X that provide different functionality for your system. The following is a more comprehensive list of the keyboard commands you know and many you may not.
A recent tweet from @superfetz reminded me of several boot commands I've learned over the years, so I thought a more comprehensive list would be useful for MacFixIt readers.
While you cannot run any code from Terminal or otherwise to set an order of boot devices, you can easily control where your Mac boots via keyboard commands. The following key combinations can be held as your Mac is powering on:
- Boot to external hard drive: Command + Option + Shift + Delete
- Boot to a bootable CD: C
- Choose start-up volume: Option
- Safe-boot mode: Shift (Note: Disables nonessential and login applications)
- Verbose mode: Command + V
- Single-user mode: Command + S
- Target disk mode: T (Note: Only for FireWire Macs)
- NetBoot (from a network server): N
- Reset PRAM: Command + Option + P + R (Note: Hold until second chime)
- Reset NV RAM: Command + Option + N + V
- Boot to open firmware: Command + Option + O + F
- Force eject (CD/DVD): Click Mouse Button and Hold
Not all these functions work with every version of Mac OS X or with every hardware upgrade, but they are the most common. Do you have any boot commands not listed here that you use? Let us know in the comments!