I find that many of the kernel extensions in /System/Library/Extensions are inapplicable to my MacBook, such as extensions for fibre channel cards, firewire, graphics cards I don't have, etc. Is there any benefit (in boot time, RAM footprint, etc.) to deleting these unneeded extensions?


Probably there is a benefit in boot up time.

  • First I would record the current boot up time (it is reported in the Console).

  • Next I would make sure to know what I am doing…

To delete actively loaded .kext, I recommended to find which ones are actually loaded.

Kext Wizard Screenshot

This will tell you exactly what is loaded, rather than just using the list from System Information. System Information might not give you everything, and Kext Wizard could find others that were loaded.


Actually, any difference in boot up time would be negligible - OS X doesn't boot /mach_kernel — it boots the kernel cache (/System/Library/Caches/com.apple.kext.caches/Startup/kernelcache), which already has the kexts you are using. This gets rebuilt if /System/Library/Extensions gets modified (or if you touch(1) it deliberately).

In terms of the filesystem space, as of Snow Leopard, everything is compressed. Meaning you're not really wasting too much space, either.

There is a downside, however — if you delete kexts, even with kext wizard, or whichever utility, there is a remote chance that some kext will be loaded on demand (e.g. via IOKit probing, on some USB device, for example). In this case, a kext might not be found - and you lose a driver.

In short, if it ain't broken, don't fix it. Leave /System/Library/Extensions intact.

  • Technologeeks and Buscar are correct. Don't touch these files at all. David Kim's answer is incorrect, illogical and unintelligible. – IconDaemon Oct 8 '14 at 12:21

While I would in general not remove anything in /System/Library/Extensions, I would consider uninstalling 3rd-party products that include a kext before doing an OS upgrade. The upgrade process seems to find and move out of the way most incompatible kexts (and those that were added in /System/Library/Extensions when they should have been in /Library/Extensions), but it's not perfect, and those can make the upgrade difficult or unstable to the point of needing to do a clean OS install and subsequent reload of apps and user data. Assuming one still wants the 3rd-party product, and did one's research to know that the new OS version was supported, one could always re-install it after the upgrade. Even more than usual, for such situations it's very wise to have a test system (or a spare disk and a lot of available downtime), since additional surprises could be expected that delay the desired end state.

Rigorous configuration control will avoid most of that; but for those that tend to test a lot of different software, install almost anything reputable, and not get rid of it once it has no further benefit, the accumulation can quickly reach a point where the expected painlessness of all things Apple vanishes entirely.


All highly suspect. Opaque binaries early in boot and thin explanations if you would even consider them explanations. Something's up.

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