Requirements
- 8GB+ USB drive with nothing important on it
- Computer running OS X
1. In Disk Utility format your USB drive as HFS+
2. Open up a terminal and mount the Yosemite Installer
sudo hdiutil attach /Applications/Install\ OS\ X\ Yosemite.app/Contents/SharedSupport/InstallESD.dmg
3. Restore the Yosemite InstallESD.dmg to your USB drive. Replace “USBDrive” with the name of your drive. You will be prompted for a Yes or No. Hit y and then Enter to continue and erase all the data on the USB drive.
sudo asr restore -source /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg -target /Volumes/USBDrive -erase -format HFS+
4. Delete and add some packages.
sudo rm /Volumes/OS\ X\ Base\ System/System/Installation/Packages
sudo cp -a /Volumes/OS\ X\ Install\ ESD/Packages /Volumes/OS\ X\ Base\ System/System/Installation/Packages
5. Copy some more files.
sudo cp -a /Volumes/OS\ X\ Install\ ESD/BaseSystem.chunklist /Volumes/OS\ X\ Base/System/
sudo cp -a /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg /Volumes/OS\ X\ Base/System/
7. Detach the USB Drive
hdiutil detach /Volumes/OS\ X\ Install\ ESD/
8. Plug the drive into a mac and start the installation.