When you Mac doesn’t boot it can be the end of the world. Hard drives are fragile and when they fail it can stop your from starting your Mac and booting. Although your Mac has a built in recovery partition it is always worth having a USB version to boot into in case your hard disk drive is toast. Creating a bootable USB drive allows you to repair your hard drive, reinstall the OS and restore from a Time Machine backup.
Create A Bootable USB Drive
The next step is to download the recovery assistant from Apple. This is a free app that we will be using. Install the app into your apps folder (I recommend the Utilities folder). Open the app and plug in your USB drive. Select it within the app. Note that you need to have FileVault disabled for this to work.
When you hit OK the app will copy across the various bits and bytes it requires to create the bootable drive. This doesn’t take too long to complete.
Once it is complete your have a bootable drive.
Using A Bootable USB Drive
Once it complete you can using your USB drive to boot into recovery mode. Restart (or start) your Mac and hold down the option key. This will allow you to pick the USB drive to boot into.
Once booted you can use the options to restore from a Time Machine backup, use Disk Utility to repair your hard drive, reinstall the OS, and get help online. It is the standard boot page which can be accessible from holding Command + R on your Mac. Normally you can boot into this drive if you hard drive is working normally.
Get Your USB Drive Back
You will notice that when you plug your bootable USB drive into your Mac that it will not appear in Finder. If you want to get back your USB drive open Disk Utilities in your Application > Utilities folder.
Select the drive from the sidebar. Use the Erase option to erase the drive, this will delete all of the data and get your USB drive as a normal drive.
It is a simple method to create a USB bootable drive. It is worth making one, sticking a label on it and put it in your draw. You never know when you need to boot into your Mac and you can’t access your hard drive.