Assuming:
- “Install OS X Yosemite.app” is located in the “Applications” folder
- USB stick has been erased/formatted and labelled UNTITLED
- USB stick is 8GB or larger
Run the following:
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/UNTITLED/ --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --nointeraction