Making a Bootable macOS Sierra Install Disk

Apple is releasing macOS Sierra some time today (or tomorrow, depending on which timezone Apple chooses to use). It’s a big (and free) update that will introduce a slew of new features and capabilities to macOS including making Siri and Apple Pay available on the Mac and extending intergation with your other Apple devices.

In case you’re wondering, Apple is also updating the naming convention of its computer operating system from OS X to macOS to match its other operating systems, iOS, watchOS, and tvOS. Have I told you macOS Sierra is free? Just like many of Apple’s past operating systems, macOS Sierra is free to download. It doesn’t cost anything.

When you’re upgrading to macOS Sierra, also known as version 10.12, you’ll be downloading a large file from the Mac App Store, just under 5GB, so you’re going to need a fast and steady connection. Given that Apple hasn’t sold a bootable DVD or USB drive installers for a while, you’re left on your own if you want or need to create a bootable installation disk, but it’s not a difficult process.

Beginning with OS X Mavericks, Apple included a very easy way for people to create a bootable installer, a tool called createinstallmedia. The steps to do this are roughly outlined on Apple Support. Apple says it’s for advanced users or system administrators but it’s safe and easy to use by anyone and it saves you the trouble and the bandwidth of having to download the OS each time you want to upgrade a Mac.

The standard steps to install the OS from the Mac App Store will delete the installer from your Mac once you’re done installing so when the prompt to install the OS appears after your download is complete, close it immediately. Do not proceed to install before making the bootable disk or you will have to redownload the installer.

Having a bootable installer makes it very practical to install macOS Sierra on as many Macs as you want. You only have to download the installer once and you can use the disk to upgrade as many compatible Macs as you can.

To make the installer, there’s a few steps:

  1. Get an 8GB USB flash drive. It can be an external hard drive or anything else but an 8GB USB flash drive is probably cheaper and more practical to use.
  2. Make sure it’s formatted as Mac OS Extended (Journaled). If it’s not, you need to open Disk Utility app, choose the flash drive from the list of external drives on the left, erase it using the Mac OS Extended (Journaled) option and GUID Partition Map.
  3. Change the name of the drive to Untitled if it’s not already (because the command is set up to target a disk called Untitled)
  4. Go to the Applications folder and check if an app called Install mac OS Sierra is in there. That’s the default location for the app when you download it from the Mac App Store.
  5. Copy the following command, open the Terminal app and paste it there. This command requires a few things; the target disk is called Untitled, the location of the downloaded installer file is in /Applications, and the installer file is called Install macOS Sierra.
sudo /Applications/Install\ macOS\ sierra.app/Contents/Resources/createinstallmedia –- volume /Volumes/Untitled —- applicationpath /Applications/Install\ macOS\ sierra.app

Press return or enter afterwards and then enter your administrator password. Usually it’s the password you use to login to your computer.

The Terminal may ask if you want to erase the destination disk. If it does, press y on the keyboard and enter. It will proceed to erase the disk and then copy the installer files. Once it’s done, you’ll have a USB disk with the name Install macOS Sierra on your Desktop.

If Terminal indicates that the process failed, go through the steps again and make sure the USB disk is inserted properly. Refrain from doing anything that might dislodge it (even if slightly) from the computer.

To use this disk to install macOS Sierra on any compatible Mac, reboot the Mac, hold the option key before the Apple logo appears and release it when the screen shows the Startup Manager disk selection options. Choose to boot from the Install macOS Sierra disk and proceed from there.

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