Apple uses its App Store to distribute its software, like new Mac operating systems. It’s convenient, but sometimes it can take a while for a download to finish. And if you have multiple Macs, it’s inefficient to download the new OS to each and every Mac.
That’s why I like to make a bootable external drive for the sole purpose of installing the Mac operating system. When I need to tend to a bunch of Macs, it’s much faster to use a bootable drive instead of going to each Mac, launching the App Store, searching for the operating system, downloading it (after entering my Apple ID), and then running the installer.
You can create a bootable USB flash drive with the macOS Sierra public beta that’s now available. The installer software will take up nearly 5GB of storage space. Here’s how to create a bootable macOS Sierra installer drive.
(Note: This tutorial uses the Sierra Public Beta. It will be updated when the final version of Sierra is released this fall.)
Download the Sierra beta installer
To get the Sierra beta in the first place, you need to sign up for the Apple Beta Software Program. Apple makes the beta available through the Mac App Store, and when you download the installer, it goes into your Applications folder.
If you already joined the program, downloaded the beta, and installed Sierra on your Mac, you might be surprised to see that your OS installer software is no longer in the Applications folder. Apple removes it after you perform an installation. You need that installer to create a bootable drive.
Don’t fret. You can download the installer again through the Mac App Store. Launch the App Store app, and then click on the Purchased tab. You should see an entry for the beta installer in your list of purchased apps. Click on the Download button, and your Mac will download the installer to your Applications folder. If it automatically launches after download, quit the installer.
Get an external drive
You can use a USB flash drive or a hard drive with room for the installer software. I’ve used different drives with success, including a VisionTek 120GB USB 3.0 Pocket Solid State Drive ($92 on Amazon) and an old 8GB Iomega Micro Mini Hard Drive.
Don’t worry if the drive isn’t formatted for the Mac. The drive will be reformatted automatically as part of the process. Change the name of your drive to Untitled; you need to do this for the steps below.
Use the Terminal to create a boot disk
So you have your external drive, and the Sierra beta installer is in place. Now you’re going to use Terminal to create a boot drive. If you’ve never used Terminal before, don’t worry. This is pretty easy. (If your really don’t want to use Terminal, there’s a free app called Diskmaker X that will make a boot drive. As of this writing, it supports El Capitan and older versions of OS X. I tried a workaround to see if I could use DiskMaker X to create a Sierra boot disk, and I got error messages. Keep an eye on DiskMaker X to see if/when it will support macOS Sierra.)
Here are the steps to create a macOS Sierra beta boot disk. (Apple also has these instructions.)
- Connect the external drive to your Mac. (In the Terminal command you will use, I use
Untitledto represent your external drive. If your drive is named something else, you need to change
Untitledto the name of your drive.)
- Launch Terminal (/Applications/Utilities/Terminal.app).
- Copy the following:
sudo /Applications/Install\ macOS\ Sierra\ Public\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Sierra\ Public\ Beta.app
- Go back to Terminal and paste the copied code at the prompt.
- Terminal will ask for a password. This is your user password. Terminal doesn’t display characters when you type it in. Hit Return.
- Terminal will tell you that it will erase your drive. To confirm that you want to continue, type Y and hit Return.
- You’ll see that Terminal erases your drive. When that part is done, your Mac may ask you if you want to use the drive for Time Machine. Click Don’t Use.
- Terminal will copy the installer file to your drive. This will take a few minutes.
- After copying, Terminal is done. You should see Terminal display a “Copy complete” and Done notice. You can quit Terminal and your drive is ready for use.
How to boot from the installer drive
- Plug your external drive into your Mac.
- Power up (or restart) your Mac. Press down on the Option key while the Mac boots.
- After a few moments, your Mac should display the Startup Manager, which will show you the available boot drives. Click on the external drive and hit Return. (You don’t need to select a network to proceed.)
- Your Mac will display an OS X Utilites window. If you want to install the beta and leave the data intact, select Install OS X. If you want to start over and wipe out the data, you need to go into Disk Utility to reformat the internal drive first, and then install macOS Sierra.
Macworld also has bootable-install-drive instructions for El Capitan (OS X 10.11), Yosemite (OS X 10.10), Mavericks (OS X 10.9), Mountain Lion (OS X 10.8), and Lion (OS X 10.7).