Few special key commands while start up. This can be of great use while troubleshooting start up issues in Mac. Action/Explanation Keystroke Eject CD on boot Hold Mouse button down immediately after powering on OS X Safe boot Press Shift during startup Start up in FireWire Target Disk mode Press T during startup Startup from a CD Press C during startup Bypass primary startup volume and seek a different startup volume Press Cmd-Opt-Shift-Delete during startup Choose Startup disk before booting Press Option during startup Start up in Verbose mode Press Cmd-V during startup Start up in Single-User mode (command line) Press Cmd-S during startup Force Powerbook screen reset Press R during startup Force OS X startup Press X during startup
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