On a sheet of Mac keyboard shortcuts for booting, one of them says, "hold down shift while booting and the computer will not load login items or extensions".

Am I wrong, or are Mac OS "extensions" something that were phased out a long time ago? (In other words, with OS X Lion, the shift key simply cancels loading the login items, period?)

Note that, of course, I know that "extensions" has meaning in other apps -- Firefox, Safari, Thunderbird, etc. But please confirm my Mac OS X suspicion as I describe it above.

(Yep, I know this is related to my other question. Getting this answer clear will allow me to resolve both questions clearly and designate their correct answers.)


Your expectation that extensions are only a thing of the past is incorrect.

Modern Mac OS X uses kernel extensions, which are not identical to the "old school" extensions used in Mac OS 9 and earlier, but yes, there are still such a thing as extensions. You can find them in /System/Library/Extensions.

Apple expands on this in this support document about Safe Mode.

  • 1
    To expand on the difference between Classic and OS X extensions: most, if not all, of the hardware drivers required by Classic Macs were included in the system software itself, not as separate extensions. In OS X most hardware drivers are provided as extensions. – username Jun 9 '12 at 14:27

To go along with @Daniel's answer: holding down the shift key on startup of OS X should prevent "startup items" from opening.

  • You've said the same thing Daniel did. How is yours an "opposite answer"? – CajunLuke Jun 9 '12 at 21:50
  • Woah! I thought "kernel extensions" and "startup items" were different things! – GEdgar Jun 10 '12 at 0:39
  • I should say: your answers are complimentary, not identical. He explained extensions then vs. now, while you specified what the keyboard shortcut does. I've edited your answer to make that more apparent. – CajunLuke Jun 10 '12 at 0:45
  • I read the document Daniel posted and it answered all the remaining questions I have! Sorry. the above apple documnet at the bottom of daniel's answer is great. THANKS -- all done. – estephan500 Jun 15 '12 at 4:24
  • @estephan500 That's a great question, and it deserves to be asked as its own question, rather than trying to get an answer here in the comments thread. – Daniel Jun 15 '12 at 4:24

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