Create OS X Yosemite Boot Disk
$ /Applications/Install\ OS\ X\ Yosemite\ Developer\ Preview.app/Contents/Resources/createinstallmedia \ --volume /Volumes/Untitled --applicationpath \ "/Applications/Install OS X Yosemite Developer Preview.app"
Set value of
--volume to your USB drive’s mount point
To determine drive mount point:
$ df -lH | grep "Filesystem"; df -lH | grep "/Volumes/*"
warning: the last stage of the Yosemite install can take a long time to complete. I have seen this on several machines. Let it run - it does finish eventually.