How to Create an OS X 10.10 Yosemite USB Installer
1. Format and Prepare USB Drive
Plug the drive into a Mac running OS X10.7 or higher and launch Disk Utility
In Disk Utility, Select the USB Flash drive from the list on the left.
Note: That you want to select the drive and not the volume. We’re using a SanDisk Cruzer flash drive, so in our case we choose 16.01 GB SanDisk Cruzer Media and not the default “No Name” volume.
With the USB drive selected, choose Partition tab on the right side of the window.
The partition scheme and volume properties of your flash drive will vary depending on manufacturer and previous configuration. In our case, our drive is brand new and formatted as a FAT volume with a Master Boot Record partition scheme. This won’t work for Yosemite, so we need to change it.
In the drop-down menu under Partition Layout, choose 1 to create a single new partition. Then click Option, choose GUID Partition Table, and click OK to save the change. Under Partition Information, Chang Format to Mac OS Extended (Journaled) and give the drive the name “Untitled” (this allows your drive to work with the Terminal commands below; you can rename the drive when the process is complete).
Press Apply to restructure the USB volume with the new parameters.
Note: that this will erase all contents of the USB drive so, as mentioned above, be sure to back up any files on the drive or use a blank drive to begin with.
2. Create the Bootable Yosemite USB Installer with Terminal
Now that your USB flash drive is ready, we can complete the process of creating a bootable Yosemite USB installer with a simple Terminal command.
Open Terminal from /Applications/Utilities and then enter the following command:
sudo /Applications/Install\ OS\ X\ Yosemite\ Beta.app/Contents/Resources/createinstallmedia –volume /Volumes/Untitled –applicationpath /Applications/Install\ OS\ X\ Yosemite\ Beta.app –nointeraction
sudo [drag-drop createinstallmedia] –volume [Flash drive path] –applicationpath [drag-drop Yosemite app path] –nointeraction
Press the Return key on your keyboard to execute the command, and enter your admin password when requested. This will create a bootable Yosemite USB installer using OS X’s createinstallmedia tool, which can take quite a while depending on the speed of your flash drive.
Let the tool do it’s thing and don’t interrupt the process until you see Terminal output Done and return your window to the user prompt. When it’s complete, your USB installer will be mounted to your Desktop and you can now rename this drive (highlight it on the Desktop and press Return)
