Trim in Yosemite

About Trim in Yosemite

In OS X 10.10 (Yosemite), Apple has introduced a new security requirement called kext signing. Kext signing works by using signatures to verify drive integrity. If a have been modified, Yosemite will no longer load the driver.

Trim Enabler support

Trim Enabler 3.3 and older worked by modifying a system driver. But thanks to Apple opening up access to their drivers and providing us with a kext certificate, you can now enable Trim safely using Trim Enabler 3.4 or Disk Sensei 1.2.

Important issues

If you try to use an older version of Trim Enabler, you could end up with the “gray stop sign” screen when trying to boot. To avoid this situation, use Trim Enabler 3.4 or later, or the new Disk Sensei. 

State of Trim in OS X

This is the updated list of OS X Trim compatibility and recommended tool to enable Trim.

prohibitory_sign

Recovering from stop sign on boot screen

If you accidentally used an older version of Trim Enabler on Yosemite

Getting back into OS X

Follow these steps to disable kext-signing and rebuild your kext cache.

Step 1: Boot recovery mode by holding Cmd+R during boot

Step 2: Is your volume encrypted (FileVault)? If so, first open Disk Utility from the menu bar and unlock/mount your drive

Step 3: Open the Terminal from the menu bar

Step 4: Run this command:

nvram boot-args

Does it say “kext-dev-mode=1”? if so, you can skip to Step 6. If it says “error getting variable”, continue with these steps:

Step 5: Run this command:

nvram boot-args=kext-dev-mode=1

Step 6: Reboot back in to Recovery Mode again

Step 7: Run these commands, replacing Your Disk Name with the name of your Mac disk volume. If the volume name contains spaces, use quotes around it.

touch /Volumes/"Your Disk Name"/System/Library/Extensions
kextcache -u /Volumes/"Your Disk name"

Step 8: Wait until it finishes (can take as long as 5-10 minutes, don’t abort it) and reboot.

You should now be back in OS X with Trim enabled.

Reversing all Trim changes

Follow these steps to undo all changes made by Trim Enabler.

Step 1: Boot recovery mode by holding Cmd+R during boot

Step 2: Is your volume encrypted (FileVault)? If so, first open Disk Utility from the menu bar and unlock/mount your drive

Step 3: Open the Terminal from the menu bar

Step 4: Run these commands, replacing Your Disk Name with the name of your Mac disk volume. If the volume name contains spaces, use quotes around it.

nvram -d boot-args
cp -rf /System/Library/Extensions/IOAHCIFamily.kext /Volumes/"Your Disk name"/System/Library/Extensions/IOAHCIFamily.kext
chown -R root:wheel /Volumes/"Your Disk name"/System/Library/Extensions
chmod -R 755 /Volumes/"Your Disk name"/System/Library/Extensions
touch /Volumes/"Your Disk name"/System/Library/Extensions
kextcache -u /Volumes/"Your Disk name"

Step 5: Wait until it finishes (can take as long as 5-10 minutes, don’t abort it) and reboot.

You should now be back in OS X with Trim disabled.

The commands are not working!

The commands will work if they are entered correctly. However, if you are not familiar with the Terminal, it can be hard to follow the steps above.

If can’t get the Terminal commands to work, or want an easier option, you can also use the Recovery Mode to reinstall OS X. Reinstalling OS X will only reinstall the system files, leaving your files and preferences untouched.

Screen Shot 2014-10-18 at 20.43.03