Need to reboot your Mac to access a new startup disc or launch with safe mode enabled so you can troubleshoot problems with OS X? Then read this list of startup options for Mac OS X machines.

Note: some of these options will not work with a firmware password installed.

Manually restart: Hold down the power button on your Mac until it shuts off. It takes about 10 seconds. Release and then press the power button again to start your Mac. Though easy, this is not the recommended shut down method as you may lose unsaved changes in open documents. Use this as a last resort when the computer is so locked up that everything else fails.

Prevent automatic login: Do you have automatic login enabled and want to disable it temporarily? Then hold down the Shift key when you see the progress indicator (looks like a spinning gear) to force your Mac to the login screen.

Disable login items and Finder windows from opening when you log in: This is handy if you want to open OS X with a minimal number of apps running. After clicking the login button in the login window, hold down the Shift key to enable this mode of strartup.

Select a startup disk: Press the Option key when you restart. If you need to open the optical drive when choosing a startup disk, press Command(⌘)-Period(.).

Start up from a CD or DVD: Press the C key when you restart.

Eject removable discs: Hold down the mouse or trackpad button or press the Media Eject key (⏏) or F12 key when you restart.

Use OS X's Recovery Tools: Press Command(⌘)-R when you restart to launch the recovery tools, which allow you to format a drive, restore the version of OS X and more.

Start up from the default NetBoot disk image: Press the N key when you restart. This allows you to access a disk image of OS X that is stored on a server and install it over a network connection.

Use Apple Diagnostics or Apple Hardware Test: Press the D key when you restart.

Start up in Target Disk Mode: Press the T key when you restart. Target Disc Mode (TDM) allows you to boot using the operating system of another Mac when your Mac is having issues. The Macs have to be compatible (same version of OS X with similar hardware configurations) and they must be connected via FireWire or Thunderbolt.

Reset parameter RAM (PRAM): Press Option-Command(⌘)-P-R when you restart. When you are having issues with your speakers, display or other peripheral items, you may be instructed by Apple's support team to reset PRAM. Settings stored here depend on your machine's configuration, but may include startup disk information, display resolution, speaker volume, and other information.

Start up in Safe Mode: When you hear the startup tone, immediately hold down the Shift key. Release the Shift key when you see the progress indicator (looks like a spinning gear). Safe Mode is useful for troubleshooting Macs as it prevents most software from automatically opening. A check of the startup volume is forced by the OS and only essential OS X items are started. As a result, some features and apps may not work correctly.

Show detailed status messages (verbose mode): Press Command(⌘)-V when you restart. Verbose mode displays text-based information about the startup process and is useful for troubleshooting issues during startup.

Start up in single user mode: Press Command(⌘)-S when you restart. Single user mode is another troubleshooting mode that allows you to interact with your Mac via text input. It's useful when you need to troubleshoot startup issues causes by a corrupted file of troublesome application. Use with caution as you can cause more problems than solve if you do not know what you are doing.

-- EdwardChrzanowski - 2015-03-18