Some people have ran into a problem with creating a bootable USB installer for the Yosemite Beta. The script located in the Installer app called “createinstallmedia” does not work quite yet on Yosemite like it did in Mavericks. I kept getting an error that told me my volume wasn’t a valid mount point.
After doing some research, I came across a post on MacRumors.com that had a workaround. Just run the following commands in Terminal and you’ll be good to go!
sudo hdiutil attach /Applications/Install\ OS\ X\ 10.10\ Developer\ Preview.app/Contents/SharedSupport/InstallESD.dmg
sudo asr restore -source /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg -target /Volumes/Untitled -erase -format HFS+
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
sudo cp -a /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg /Volumes/OS\ X\ Install\ ESD/BaseSystem.chunklist /Volumes/OS\ X\ Base\ System
Make sure to change “/Volumes/Untitled” to the correct name of the disk you are trying to install it on!
Happy OS beta testing!