how to create a bootable USB key in macOS?

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Creating a bootable USB drive in Mac OS X or macOS is very useful when it comes to reinstalling the operating system after a problem with the hard drive. You can also use the system tools without them being launched from one of the partitions of the disk, or even install the complete system on a machine without internet access.

Create a bootable installer for macOS is a straightforward process, but still requires a little time and patience. You can install the operating system of your Mac using an external drive (USB flash drive, external hard drive) or secondary volume as the startup drive. On the other hand, know that it is not necessary create a bootable installer if you just want to reinstall macOS or reset your Mac to factory condition (to sell it, for example).

The items required to create a bootable macOS USB drive

Two software to simplify your life (excluding macOS Big Sur)

There are two easy-to-use software for creating bootable macOS USB drives: DiskMaker X and Keylifornia. These two software will take care of doing the work for you and we strongly recommend that you follow their tutorials. On the other hand and if you wish create a bootable USB drive for macOS Big Sur, these software are not, at the time of this writing, by still compatible with this version of the system. Remember to check their respective sites, things may have changed by then. If it still isn’t, don’t panic, here’s how to do it manually on macOS Big Sur.

Create a bootable USB (for macOS Big Sur specifically)

  • Download the installer for macOS Big Sur
  • Connect your USB stick
  • Open the app Terminal
  • Type the following command line:
sudo /Applications/Install macOS Big Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/nomdevotrecléUSB
  • Press on Entrance
  • Enter your session password (it will not be displayed but this is normal)
  • Press the touch Y
  • Accept, then wait.

Booting your bootable USB drive (for macOS Big Sur specifically)

  • On Mac Intel, hold down the Option (⌥) key while your Mac is starting up and select Install macOS Big Sur
  • On Mac Apple Silicon, hold down the Touch ID key when starting your Mac and also select Install macOS Big Sur
  • In both cases, then follow the installer.

How to create a bootable USB drive with a macOS install partition (excluding macOS Big Sur)

First of all, you will need to have a USB key, SD card or any other empty medium with at least 12 GB of free space, and download the installer for your operating system again. It comes in the form of a seemingly all-classic app. However, it has the particularity of self-destructing once the installation program is finished.

os-x-mac-app-store-purchases-opt-alt

  • Press and hold the key alt or Option (⌥), then click Purchases at the top of the window
  • You can also enter the name of the system directly in the search box (macOS Mojave for example)
  • You should find in the list your current operating system and also other versions of macOS that you had previously installed
  • Choose the version that suits you then click either on Download, be sure cloud icon
Downloading the entire operating system may take a while ... now's the time to go get yourself some coffee!
Downloading the entire operating system may take a while… now’s the time to go get yourself some coffee!

While the system installer application is downloading, we will format the USB drive.

You can also access Spotlight in the blink of an eye by pressing the Cmd and space keys on your keyboard
You can also access Spotlight at a glance by pressing the command and space keys on your keyboard
  • Open the app Disk Utility
  • Plug in your USB key, and select it
  • In the right area, go to the tab Partition
Select the correct USB drive in Disk Utility
Warning: your USB key is represented by the parent element, the other elements below are the partition (s).
  • In Partition scheme choose 1 partition
  • In Partition Information choose boot as name (this allows us to give you a ready-made copy / paste command), in format choose Mac OS Extended (Journaled)
You must name your boot partition at this stage.  If so, you will need to modify the terminal commands to reflect the change.
You must name your partition “boot” at this stage. If so, you will need to modify the terminal commands to reflect the change.
  • Click on Options…, select GUID Partition Table, then click okay
The partition table must be GUID for your Mac to recognize your key / hard drive / memory card as a bootable volume
The partition table must be GUID for your Mac to recognize your key / hard drive / memory card as a bootable volume

Partition

  • Click on Partition

Now, we’re going to use a command line utility – included in the macOS installer package since version 10.7 – that greatly simplifies the creation of a bootable USB drive. The command in question depends on the operating system you downloaded.

  • Open the app Terminal using Spotlight for example

Spotlight is handy, but there are also alternatives, like Quicksilver

Copy the command corresponding to the operating system you downloaded:

macOS High Sierra

sudo /Applications/Install macOS High Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume 

macOS Sierra

sudo /Applications/Install macOS Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install macOS Sierra.app

macOS El Capitan

sudo /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/boot --applicationpath /Applications/Install OS X El Capitan.app --nointeraction

macOS Yosemite

sudo /Applications/Install OS X Yosemite.app/Contents/Resources/createinstallmedia  --volume /Volumes/boot --applicationpath /Applications/Install OS X Yosemite.app --nointeraction

macOS Mavericks

sudo /Applications/Install OS X Mavericks.app/Contents/Resources/createinstallmedia  --volume /Volumes/boot --applicationpath /Applications/Install OS X Mavericks.app --nointeraction

You will be prompted for a password – enter your session password then hit Enter

os-x-terminal-sudo-createinstallmedia
Nothing happens when you type? It’s normal ! This is a security mechanism to hide your password from prying eyes. Type as if nothing had happened.

The operating system is being transferred. This may take up to 20 minutes depending on the media to which the system is transferred. Be patient. Your terminal window should look like this when finished:

os-x-terminal-sudo-createinstallmedia-done

If during this time you want to know where the process is, you can go to the Activity monitor (accessible via Spotlight), go to the tab Disk click at the top of the column Operation name and find the process createinstallmedia. In the column Burned bytes you can follow the progress (the complete image is about 5.5 GB).

Boot the installation of macOS from your USB key

To boot the installation of macOS from your USB key, there are two methods. One assumes that you still have access to your system on your hard drive, the other works in all other cases.

From macOS

  • Plug in your bootable USB stick

Apple, system preferences

  • Go to the menu  at the top left of your screen, then in System Preferences …
When you use the search field of this window, the searched application is highlighted
When you use the search field of this window, the searched application is highlighted
  • Go to Boot disk

os-x-boot-disk-select-install-os-x-restart

  • Select Install OS X [nom du système] then click on To restart…

When the computer starts

  • Computer off, plug in your bootable USB drive
  • Turn on the computer and immediately press the alt orOption (⌥)
  • Choose the volume whose name begins with Install OS X.
  • That’s it !



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