What if you want to perform a clean install, completely erasing your startup drive? Or perhaps you’d like to have the installer on a bootable USB drive, so you don’t have to keep downloading it every time you wish to upgrade one of your Macs? The problem is you cannot upgrade another Mac without downloading the installer all over again. The workaround is to create a bootable USB flash drive containing the OS X Yosemite installer.
Use Disk Utility to Create a Bootable OS X Yosemite Installer
You can create a bootable installer in two ways. The first is to use a hidden Terminal command that can handle all of the heavy lifting for you. The second is more manual and time-intensive. It uses the Finder and Disk Utility apps. This article will take you through the steps to manually create a bootable copy of the OS X Yosemite installer.
What You Need
OS X Yosemite installer. You can download the installer from the Mac App Store. Once complete, you’ll find the download in the /Applications/ folder, with the file name Install OS X Yosemite. A USB flash drive or another suitable bootable device. As mentioned, you can use a hard drive or an SSD for the bootable device, although these instructions will refer to a USB flash drive. A Mac that meets the minimum requirements for OS X Yosemite.
The process for creating a bootable copy of the OS X Yosemite installer follows these basic steps:
How to Mount the OS X Yosemite Installer
Deep within the Install,OS X Yosemite file that you downloaded is a disk image that contains all of the files you need to create your own bootable installer. The first step is to gain access to this file.
How to Use Disk Utility to Clone the OS X Install ESD Image
The next step is to use Disk Utility’s Restore feature to create a clone of the OS X Install ESD image you mounted on your desktop. Doing so will mount the InstallESD image on your Mac desktop and open a Finder window displaying the contents of the mounted file.
How to Modify the OS X Base System on Your Flash Drive
All that’s left to do is modify the OS X Base System (the flash drive) to make the OS X Yosemite installer work correctly from a bootable device. Your USB flash drive is now ready to be used as a bootable OS X Yosemite installer. Leave the Installation window open, because we’ll use it below. You can boot from the Yosemite installer you just made by inserting the USB flash drive into your Mac, and then starting your Mac while holding down the option key. The computer will start at the Apple boot manager, which will let you select the device you wish to start up from.
