AppleReviewGuy has a script that simplifies most of this, but I thought it would be nice to see a guide.
I am NOT responsible if you screw up your system. Not for noobs.
1. Aquire the OS X 10.10 Installation application.
2. Right click on it to "Show Package Contents"
3. Inside the app, go to 'Contents/SharedSupport' and mount InstallESD.dmg.
4. Open Terminal and run 'cd /Volumes/OS\ X\ Install\ ESD/' then 'open BaseSystem.dmg'.
5. Open Disk Utility, select your Thumbdrive (It needs to be larger than 6GB, I think.) and make 2 partitions, BOOT and Installer. Before you click 'Apply' click 'Options' and select 'Master Boot Record'.
6. Click 'Ok' then 'Apply' then wait for a bit.
7. Select 'Installer' in the Disk Utility list then go to 'Restore' (at the top).
8. Drag the mounted BaseSystem.dmg (white one, not the file with the disk on it) into the Source field and drag 'Installer' (from the disk util list) into the Destination field.
9. Click restore and get some coffee, long night ahead.
10. Alright, good job, download the Clover package
here
11. Run the installer, but MAKE SURE you change the install location to your 'BOOT' drive. Also make sure your options you chose look like this:
Image
12. Almost ready to reboot, just download
this config.plist and place it into the root of your BOOT drive.
13. Run the bless command in terminal (sudo bless --folder=/Volumes/BOOT --file=/Volumes/BOOT/EFI/BOOT/BOOTX64.efi --setBoot --legacy)
14. Reboot, when you hear the bong, hold option until the drive select menu appears.
15. Select 'Windows' and wait for a bit. When that appears, just make sure you select 'Boot OS X from Installer'
16. Wait a bit again, then the OS X Yose installer should appear. Run through it, make sure you select the partition you want to be Yose.
17. Reboot and run through steps 14 and 15, but this time it should boot into the First time Setup wizard.
18. Whenever you reach your desktop, if audio is broken get
this and run it.
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its there.