In order to create OSX installer on USB memory drive you need to:

  • Download the Mac OSX Yosemite installer from AppStore on you Mac.
  • Create installation media from Terminal by executing following command (remember to adjust YOURUSBVOLUME value):

    sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/YOURUSBVOLUME --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --nointeraction
  • Boot target Mac from USB by pressing ALT/OPTION key while powering-on the computer.
  • Remember to format target drive first with Disk Utility if you want to perform clean installation.