Disable macOS 11 (Big Sur) 'kernel_task' which is throttling the CPU

WARNING ALERT: This ONLY relates to someone who has deleted the IOPlatformPluginFamily.kext in previous versions of macOS to sort the kernel_task overloading the CPU but now after installing macOS 11 (Big Sur) the problem has started again. You will be deleting a system extension and taking a risk... so you have been WARNED! + also best to use version 11.1 upwards, since when testing with 11.0.1 I found it very buggy!

So here is the problem...

After booting up the MacBook Pro the macOS would be running unbelievably slow. When opening the Activity Monitor to see what was happening with the CPU the thing at the top of the list was the kernel_task using around 500%!

In any of the previous versions - macOS 10.14 (Mojave) or below it was a fairly easy fix by first running recovery mode CMD + R and in the terminal.

csrutil disable

Then running single user mode CMD + S.

fsck -fy

mount -uw /

sudo mkdir /IOPlatformPluginFamily-backup-kexts/

sudo mv /System/Library/Extensions/IOPlatformPluginFamily.kext /IOPlatformPluginFamily-backup-kexts/

sudo rm -rf /System/Library/Extensions/IOPlatformPluginFamily.kext

But from macOS 10.15 (Catalina) onwards this has stopped working. The reason being that Apple introduced the read-only system volume which is a dedicated partition for only storing system content which prevents any tampering with system files which one of them is the troublesome IOPlatformPluginFamily.kext.

Now before finding the solution below which relates to macOS 11 (Big Sur) I had tried making a bootable USB running macOS 10.14 (Mojave) but this couldn't read the read-only system volume.

Step 1 - Disable FileVault

Go to System Preferences -> Security & Privacy and choose the FileVault tab. Then select Turn Off FileVault.

Step 2 - Bypassing the Signed System Volume (SSV*)

SSV helps prevent tampering with any Apple software that is part of the operating system. Additionally, it makes macOS Software Update more reliable and much safer. SSV utilizes APFS snapshots, so if an update cannot be performed, the old system version can be restored without reinstallation.

So this means that macOS Big Sur actually no longer boots from the live system volume but now boots from a snapshot/copy of the same system folder. Normally it's impossible to mount a snapshot as writable, only readable so here is the solution I have found.

So at first bootup in Recovery Mode using CMD + R. On the screen that loads go to the navigation and choose Utilities -> Terminal. Input the following.

NOTE: Without this being done first you won't have permissions to carry out the next csrutil authenticated-root disable command.

csrutil disable

Then.

reboot

Straight away bootup in Recovery Mode again using CMD + R and choose Utilities -> Terminal. Input the following.

csrutil authenticated-root disable

Then.

reboot

Step 3 - Mount the Live Volume and backup the IOPlatformPluginFamily.kext file

Now reboot back into the normal macOS boot mode and let us mount the live volume - the disk1s5 could be different.

NOTE: To find out if 'disks5' is correct for your machine enter diskutil list in the terminal which will list your drives.

diskutil mount disk1s5

Next make it writable which will require you to enter your password - the /Volumes/Macintosh\ HD\ 1 could be different.

sudo mount -uw /Volumes/Macintosh\ HD\ 1

Password:

Now let's first see that the offending IOPlatformPluginFamily.kext file exists by entering.

ls -a /Volumes/Macintosh\ HD\ 1/System/Library/Extensions/

Rather than deleting the file we will do a backup - so use the below and move it to a newly created folder.

sudo mkdir /Volumes/Macintosh\ HD\ 1/IOPlatformPluginFamily-backup-kexts/

sudo mv /Volumes/Macintosh\ HD\ 1/System/Library/Extensions/IOPlatformPluginFamily.kext /Volumes/Macintosh\ HD\ 1/IOPlatformPluginFamily-backup-kexts/

Again see if it has disappeared from the directory.

ls -a /Volumes/Macintosh\ HD\ 1/System/Library/Extensions/

Step 4 - Create snapshot and tag it for the next default reboot.

Now we have deleted the file we need to add this new version of the system folder as a snapshot so enter the following.

sudo /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs_systemsnapshot -s "SnapshotName" -v /Volumes/Macintosh\ HD\ 1

Then tag this as a our default for the next reboot.

sudo /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs_systemsnapshot -r "SnapshotName" -v /Volumes/Macintosh\ HD\ 1

Now fingers crossed you should be able to reboot and the kernel_task should no longer be hogging the CPU as before and in return slowing your machine down.