Understanding the Kext Cache
In macOS, a Kernel Extension (or “kext”) is a specialized piece of code that runs directly within the core operating system kernel. Kexts are typically used for hardware drivers, deep-level antivirus software, and virtual machine hypervisors. Because loading hundreds of individual kext files during startup would drastically slow down boot times, macOS compiles all approved kernel extensions into a single, optimized file known as the Kext Cache.
If you recently installed or uninstalled complex software (like a VPN client, an audio routing app like BlackHole, or older hardware drivers) and your Mac is suddenly crashing, failing to boot properly, or refusing to recognize a device, the Kext Cache has likely become corrupted or desynchronized. Rebuilding it via the Terminal forces macOS to throw away the old cache and generate a fresh, accurate one.
How to Rebuild the Cache
Because you are interacting directly with the kernel, you must execute this command with administrative (sudo) privileges.
- Open the Terminal application (located in Applications > Utilities).
- Type the following command and press Enter:
sudo kextcache -i /- The Terminal will prompt you for your password. As you type, the characters will remain invisible. Press Enter when finished.
Analyzing the Output
The -i / flag tells the utility to invalidate and rebuild the cache for the root volume (/). The process can take anywhere from a few seconds to a few minutes, depending on the speed of your Mac and the number of third-party extensions installed.
You will see a flurry of text scroll across the screen. You may see warnings like Kext rejected due to improper signature or Omitting framework. Do not panic; this is completely normal. Apple’s system integrity checks are extremely strict, and the utility is simply notifying you that it is ignoring improperly signed or outdated extensions (which is exactly what you want it to do).
Finalizing the Rebuild
Once the prompt returns and you see your username again, the rebuild is complete. However, the macOS kernel cannot swap out the cache while it is actively running.
You must restart your Mac for the new Kext Cache to take effect. Click the Apple logo in the top left corner and select Restart. Your next boot may take slightly longer than usual as the kernel parses the fresh cache, but your driver conflicts and kernel panics should be completely resolved.