Booting a Mac

1. Hold down the C key at startup to boot from a CD.
2. Hold down the T key at startup to boot current Mac as a firewire drive on another Mac. Called Firewire Target Disk Mode.
3. Command-S boots into Single-User mode.
4. Command-V boots into Verbose mode, displaying all startup text.
   1. To be verbose at every bootup:
      $ sudo nvram boot-args="-v"
   2. To turn it off:
      $ sudo nvram boot-args=""
5. Hold down the Shift key to boot into Safe Mode (or "Safe Boot"),
   suppressing all non-basic Kernel extensions ("Kexts"), plus /System/Library/StartupItems.
   If Journaling is not enabled, fsck will run. Journaling is enabled in the Disk Utility.
   If Journaling is enabled, fsck should not be run, since they can conflict.
   1. Kernel Extensions can cause conflicts. Command-drag stuff out of System/Library/Extensions. Command-dragging moves a file to the Desktop, whereas simple dragging just copies file to the Desktop.
6. Hold down the left mouse button at boot to eject a CD from your drive, before booting the system.
7. Hold down the Option key at boot to access the Startup manager, to select the OS.
8. Shift-Option-Command-Q logs you out without prompting.
9. Shift-Option-Command-Delete (above return key) will force your mac to boot from any drive other than the default. [Thanks to Andy @ Clinical Sciences Centre (CSC)]
10. If the Mac won't boot, hold down the X key until you see the OSX logo, to boot from the internal drive.
11. Zap the Pram by holding down Command-Option-P-R at bootup until the Mac chimes 3 times.
12. You can boot from the OSX Install-disk, launch Disk Utility, click First Aid, then Repair Permissions.
13. You can hold down the Shift key when logging into a user account, and wait for the Desktop to appear, suppressing the Login items.
14. If the Mac is set up to boot into your account automatically, hold down the Shift key right after the bluescreen OSX logo appears. This will bypass Safe-boot and force the Login window to appear, as opposed to bypassing it automatically, like normal.
15. When you boot up, you can enter >console as the username and no password and then hit the Login button, you'll entering a text-only mode, and presented with another login prompt. Type reboot to re-enter the GUI mode.