Twitter user Jaroneko published some instructions on how to create a bootable USB for OS X 10.10 the other day.
This is a revised edition tweaked by me to address a couple of the errors terminal was spewing out in response to Jaroneko's instructions, as well as improving the clarity of the process with exercising the verbose option.
If OS X 10.10 Developer Preview.app is in /Downloads:
- defaults write com.apple.finder AppleShowAllFiles TRUE
- killall Finder
- sudo hdiutil attach ~/Downloads/Install\ OS\ X\ 10.10\ Developer\ Preview.app/Contents/SharedSupport/InstallESD.dmg
- diskutil list (Find the /dev/disk corrosponding to your USB stick).
- Unmount USB Untitled Partion in Disk Utility
- sudo asr restore -source /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg -target /dev/disk2 -erase -format HFS+ (CHECK DISK 2 IS THE RIGHT ONE WITH DISKUTIL BEFORE ENTERING THIS).
- sudo rm /Volumes/OS\ X\ Base\ System/System/Installation/Packages (If you have any issues here, remove your USB stick and re-insert it into the other port and try again. That tends to clear up the issue for some reason).
- sudo cp -a -v /Volumes/OS\ X\ Install\ ESD/Packages /Volumes/OS\ X\ Base\ System/System/Installation/Packages
- sudo cp -a -v /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg /Volumes/OS\ X\ Install\ ESD/BaseSystem.chunklist /Volumes/OS\ X\ Base\ System
If OS X 10.10 Developer Preview.app is in /Applications:
- defaults write com.apple.finder AppleShowAllFiles TRUE
- killall Finder
- sudo hdiutil attach /Applications/Install\ OS\ X\ 10.10\ Developer\ Preview.app/Contents/SharedSupport/InstallESD.dmg
- diskutil list (Find the /dev/disk corrosponding to your USB stick).
- Unmount USB Untitled Partion in Disk Utility
- sudo asr restore -source /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg -target /dev/disk2 -erase -format HFS+ (CHECK DISK 2 IS THE RIGHT ONE WITH DISKUTIL BEFORE ENTERING THIS).
- sudo rm /Volumes/OS\ X\ Base\ System/System/Installation/Packages (If you have any issues here, remove your USB stick and re-insert it into the other port and try again. That tends to clear up the issue for some reason).
- sudo cp -a -v /Volumes/OS\ X\ Install\ ESD/Packages /Volumes/OS\ X\ Base\ System/System/Installation/Packages
- sudo cp -a -v /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg /Volumes/OS\ X\ Install\ ESD/BaseSystem.chunklist /Volumes/OS\ X\ Base\ System
After you've completed this script you may wish to execute defaults write com.apple.finder AppleShowAllFiles FALSE, then killall Finder in the Terminal to re-hide hidden folders.
As ever, please make a backup before updating to a beta edition.