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how to create a bootable macOS installer

If you are preparing to install macOS on multiple computers, one of the things that can make your life simpler (and the waiting shorter) is a bootable USB installer.

The idea of the installer is that you only need to download the macOS from the App Store once. Usually, when you run the installer after downloading it, it’ll delete itself and you have to go through the whole download process again on each machine or disk that you want to install macOS onto. By making a bootable USB drive, you simply plug the drive in to your mac, launch the installer app and tell it where to install the OS. You can repeat this as many times as you like as the installer will remain safe on your USB.

There are various ways to make a bootable USB installer, but they all involve the same process:

1. Download the macOS Installer from the App Store.
2. Run the createinstallmedia command from the Terminal, an AppleScript or a helper app.
3. Reboot your mac, choosing the newly created USB as the startup disk.
4. Run the from the USB.

Step 2 is where the fun is. The createinstallmedia command can be tricky to get right, particularly if you’re not familiar with working on the command line. For those of you that are, follow Apple’s instructions here.

For a little more convenience, I wrapped all that inside an AppleScript which will first ask you for the location of the installer, then ask you to choose the USB target.

For maximum convenience, I also wrote a free little Swift app I’ve dubbed ‘Boot Buddy‘ (cos “Create bootable macOS Installer” just didn’t quite have the right ring to it..!) that will present the whole thing in a neat little user interface. Three clicks, more or less, and you’re done.

Boot Buddy doesn’t require an admin password to install, but you do need to provide an admin password to actually create the bootable installer as the createinstallmedia process has to be run as root. Boot Buddy doesn’t see or use this in any way whatsoever other than to start the createinstallmedia process or to cancel it (if you choose to do so); authorisation is handed off to macOS to take care of.

Boot Buddy requires macOS 10.11 or higher and can create bootable USBs from Mavericks, Yosemite, El Capitan, Sierra and High Sierra installer apps.

Share and enjoy! 🙂

make a Sierra USB bootable installer

Screen Shot 2016-08-21 at 13.06.29
For those participating in Apple’s public beta program or developer program, here’s a script that will make a bootable flash drive installer of Sierra for you. Of course, you’ll need to have downloaded and saved the original installer before running it on your mac for this to work.

When an installer is made available to you from Apple, the first thing to do after downloading it is to quit the installer if it auto runs. Insert your blank USB thumb drive, and make sure it’s at least 8GB (16GB recommended).

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You can either run the script immediately with the installer app still in your /Applications or /Downloads folder, or you can move the installer first to your preferred location. It doesn’t make any difference to the script since it’ll ask you for the location of both the Installer and the USB drive before doing its thing. It’ll also give you an option to cancel out if you made any mistake in specifying the location or you just change your mind. The script will ask you for an administrator password as it needs elevated privileges to run the createInstallMedia routine.

Note the script continues to run in the background until the installer has been created. It sleeps for an interval of 10 secs between checking the job status. Since it takes around ten minutes for the createInstallMedia routine to finish its work, you could comfortably increase that sleep time 30 secs or more if you desire. The script will present you a dialog when it detects all is done:

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To use the bootable installer, just pop it into a mac, reboot holding down the ‘option’ key and choose the USB drive to kick off the installation process on a partition of your choice.

The full script is available here.


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