How to Boot a Mac from a USB: Creating a Bootable USB with MacOS

Do you know how to boot a Mac from a USB? Do you have an iMac or a Macbook Pro already with a few years under its belt and want to give it new life by installing a new solid hard drive SSD? Do you want to install Apple’s operating system from scratch on your Mac?

The first thing to do before changing the hard disk or before installing the new OS is to prepare a USB stick with MacOS to reinstall the operating system on our Macbook.

How to boot a Mac from a USB with the Option (⌥) key?

Start the Boot Manager, which allows you to choose other disks or boot volumes if available.

Is it better to do this than recovering a copy of Time Machine? Yes. Since we want to improve the performance of our computer: it is best to perform a completely clean installation and then copy only the data and programs that interest us.

How to create an executable USB with MacOS

Apple has finally made things easy for us and we don’t have to do very complicated things to create an executable USB disk that allows us to install MacOS from scratch. These are the steps to follow.

  • Download the latest macOS installer (Sierra or Mojave) from the Mac App Store. Close the installer if it opens automatically once downloaded. The installer will be in the Applications folder.
  • Mount the USB flash drive and with the Mac Disk Utility and format it HFS+ (GUID partition). Name it MyVolume.
  • Open the Terminal app, located in the Applications>Utilities folder
  • Paste the following commands depending on the MacOS operating system you have chosen (only one of the four commands depending on the Apple operating system you have chosen):
sudo /Applications/Install\ macOS\ --volume /Volumes/MyVolume

sudo /Applications/Install\ macOS\ High\ --volume /Volumes/MyVolume

sudo /Applications/Install\ macOS\ --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\

sudo /Applications/Install\ OS\ X\ El\ --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\

In a few minutes, we will have the installer available on our USB flash drive.

Now it will depend on what you want to do:

  • After changing the RAM and inserting the new SSD hard drive, restart the Macbook or iMac and press and hold the ALT key to display the boot selector (choose MyVolume).
  • If you only want to install the new MacOS from scratch, you must restart the Macbook or iMac, and keep the ALT key pressed so that the boot selector appears (choose MyVolume).

Finally, install MacOS on the new SSD hard drive.

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