As seen on Apple’s website
To start up into Safe Mode (to Safe Boot), do this:
- Be sure your Mac is shut down.
- Press the power button.
- Immediately after you hear the startup tone, hold the Shift key. The Shift key should be held as soon as possible after the startup tone, but not before the tone.
- Release the Shift key when you see the gray Apple icon and the progress indicator (looks like a spinning gear).
During startup in Mac OS X v10.4 through Mac OS X v10.6.8, you will see “Safe Boot” on the login window, which appears even if you normally log in automatically. During startup in Mac OS X v10.2 through v10.3.9, you will see “Safe Boot” on the Mac OS X startup screen.
To leave Safe Mode, restart the computer normally, without holding any keys during startup.
Other interesting boot modes:
Keystroke Description Press C during startup Start up from a bootable CD or DVD, such as the Mac OS X Install disc that came with the computer. Press D during startup Start up in Apple Hardware Test (AHT). Press Option-Command-P-R until you hear startup sound a second time. Reset NVRAM Press Option during startup Start up in Startup Manager, where you can select a Mac OS X volume to start from. Note: Press N to make the the first bootable Network volume appear as well. Press Eject, F12, or hold the mouse or trackpad button Ejects any removable media, such as an optical disc. Press N during startup Attempt to start up from a compatible network server (NetBoot). Press T during startup Start up in Target Disk Mode. Press Shift during startup Start up in Safe Boot mode and temporarily disable login items. Press Command-V during startup Start up in Verbose mode. Press Command-S during startup Start up in Single-User mode. Press Option-N during startup Start from a NetBoot server using the default boot image. Press Command-R during startup Start from Lion Recovery1