[3/7/2017 update: Just a reminder that Apple has released a good number of major updates to macOS 10.12 Sierra since its initial release. Unfortunately, if you created an installer drive with an older version of the Sierra installer, you can’t easily update the installer drive so that it installs the latest version of Sierra. If you want to create a bootable drive that installs the latest version of 10.12 directly, you’ll need to a download the latest version of the Sierra installer from the Mac App Store, and then repeat the procedure below using that newer installer app.]
I’ve long recommended creating a bootable installer drive—on an external hard drive, thumb drive, or USB stick—for the version of OS X you’re running on your Mac.1 It’s great for installing the OS on multiple Macs, because you don’t have to download the ~5GB installer onto each computer, and it serves as a handy emergency disk if your Mac is experiencing problems. 2 Here’s this year’s version, for macOS Sierra (formerly known as OS X 10.12), of my annual how-to guide.
How do I get the Sierra installer?
What you need
To create a bootable Sierra installer drive, you just need the aforementioned Sierra installer and a Mac-formatted drive (a hard drive, solid-state drive [SSD], thumb drive, or USB stick) that’s big enough to hold the installer and all its data—an 8GB thumb drive is perfect. Your OS X user account must also have administrator privileges.
Your drive must be formatted as a Mac OS Extended (Journaled) volume with a GUID Partition Table. Macworld has a nice tutorial that explains how to properly format the drive.
Important: When you download the Sierra installer from the Mac App Store, it will be saved to your main Applications folder (/Applications); it must be in that location for the procedure below to work. However, if you run the installer—say, to install Sierra—from that location, the installer will delete itself after installation finishes. So if you plan to run the installer before making your bootable installer drive, first make a copy of the Installer in another folder or on another drive; before creating the bootable installer, move the installer back to the Applications folder. (If you’ve read this paragraph too late, and the installer has already deleted itself after an installation, you just need to re-download Sierra from the Mac App Store—via the Purchases tab—before you can make your bootable installer drive.)
The easiest way is createinstallmedia
Starting with Mavericks, hidden inside the OS X installer is a Unix program called createinstallmedia, provided by Apple specifically for creating a bootable installer drive. Using it requires the use of Terminal, but it works well, it’s official, and the procedure is easy enough: If you can copy and paste, you can do it.3
The only real drawback to createinstallmedia is that it doesn’t work under OS X 10.6 Snow Leopard—it requires OS X 10.7 Lion or later. But I suspect that the vast (vast) majority of people installing macOS 10.12 Sierra will have access to a Mac running 10.7 or later.
- Connect to your Mac a properly formatted 8GB (or larger) drive, and rename the drive
Untitled. (The Terminal command I provide here assumes that the drive is named Untitled.) Also, make sure that the Sierra installer (or at least a copy of it), called Install macOS Sierra.app, is in its default location in your main Applications folder (/Applications).
- Select the text of the Terminal command below, and copy it:
sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Sierra.app --nointeraction
--) were replaced by em dashes (—); press Return.
The Terminal window displays createinstallmedia’s progress as a textual representation of a progress bar: Erasing Disk: 0%… 10 percent…20 percent… and so on. You also see a list of the program’s tasks as they occur: Copying installer files to disk… Copy complete. Making disk bootable… Copying boot files… Copy complete. On a recent Mac with a fast destination drive, the procedure shouldn’t take longer than 5 minutes, though it can take as long as 20 or 30 minutes on an older Mac or with a very slow drive. The process is finished once you see Copy Complete. Done., as shown in the screenshot above. If you like, you can then rename the drive (in the Finder) from its default name of Install macOS Sierra Developer Beta or Install macOS Sierra Public Beta.
Booting from the installer drive
You can boot any Sierra-compatible Mac from your new installer drive. First, connect the drive to your Mac. Then, if your Mac is already booted into OS X, choose the install drive in the Startup Disk pane of System Preferences and restart; or, if your Mac is currently shut down, hold down the Option key at startup and choose the install drive when OS X’s Startup Manager appears.
Once booted from your installer drive, you can perform any of the tasks available from the OS X installer’s special recovery and restore features. In fact, you’ll see the same OS X Utilities screen you get when you boot into OS X Recovery—but unlike with recovery mode, your bootable installer includes the entire installer.
Comments or questions? @danfrakes on Twitter or email me at siteemail at this domain.
- When I was at Macworld, my most popular article each year was my annual bootable-installer tutorial. Each still remains at or near the top of Google results for “bootable installer,” including the one I did for OS X 10.11 El Capitan last year. ↩
- I think it’s a better emergency disk than OS X Recovery, because a bootable installer drive includes the full OS X installer, whereas OS X Recovery requires you to download ~5GB of installer data if you ever need to reinstall the OS. (And don’t forget that not all Macs have OS X Recovery.) ↩
In some of my older Macworld articles on creating a bootable installer drive, I provided three or four different ways to perform the procedure, partly because some procedures didn’t work on some versions of OS X, and partly to allow Terminal-averse people to use graphical-interface apps. But the Terminal method will work for the vast majority of people these days, and while Terminal’s textual interface can be intimidating, in this particular case there are actually fewer opportunities to make an error. ↩