How to Make a Bootable OS X Yosemite USB Install Key

These are instructions on how to make a bootable OS X Yosemite USB key.

Step One
Connect a 8GB or larger USB key to your computer.


Step Two
On a Mac that can run OS X Yosemite, open Apple's How to download and install macOS page in Safari and click Yosemite 10.10 under 'Download via web browser'. The InstallMacOSX.dmg disk image downloads to your Downloads folder. Apple no longer sells OS X Yosemite in the Mac App Store; this download is free. More download options are in Where to Download OS X Yosemite.

Double-click InstallMacOSX.dmg to open it, then double-click InstallMacOSX.pkg and follow the onscreen instructions. This puts the Install OS X Yosemite app in your Applications folder. If the Mac isn't compatible with OS X Yosemite, the package won't complete.

Step Three
Launch Disk Utility from the Applications:Utilities folder.


Step Four
Select your USB thumb drive from the list on the left and click the Partition tab.


Step Five
Set the Partition Layout to 1 Partition, set the Name to 'Yosemite', and set the Format to Mac OS Extended (Journaled).


Step Six
Click the Options button then choose GUID Partition Table from the popup window then click the OK button.


Step Seven
Next click the Apply button to save your changes. When asked to confirm click the Partition button.




On OS X El Capitan or later, Disk Utility has no Partition tab: select the USB drive, click Erase, name it 'Yosemite', choose Mac OS Extended (Journaled) and GUID Partition Map, then click Erase.

Step Eight
Launch Terminal from the Applications:Utilities folder.


Step Nine
Make sure your empty USB key is still inserted. Additionally, make sure you do not have any other volumes named 'Yosemite' except for the one we just created in Step Five.


Execute the following command in the Terminal window to create your OS X Yosemite Install key.

sudo '/Applications/Install OS X Yosemite.app/Contents/Resources/createinstallmedia' --volume '/Volumes/Yosemite' --applicationpath '/Applications/Install OS X Yosemite.app' --nointeraction


You will be asked to enter your Administrative account password.


Step Ten
After about 15 minutes the creation of your USB Install Key for OS X Yosemite will be complete.


Step Eleven
You may now restart your Mac and hold down the Option key after hearing the boot sound. You'll be presented with a list of bootable drives. Select the USB install key. Yosemite runs only on Intel Macs, so this is the startup to use.