How to create a bootable macOS Big Sur drive and use it to install from scratch

Although Big Sur is currently in beta phase, it can create a bootable external drive with which to perform a clean installation of the system Is very useful. In this way we can completely remove the previous installation and create a new one that, in theory at least, should have better performance and fewer failures.

What we need to create a bootable USB with macOS Big Sur

For this process we will need a flash memory of at least 16GB of storage. Keep in mind that we will completely erase your content, so if necessary, we will save the files in another location.

We will also need a copy of the Big Sur setup application. We can get this app through the developer portal or through the public beta.

Last but not least, the Mac with which we create the installer, even if it is intended for another Mac, must be compatible with Big Sur.

Terminal, here we go

Well, the necessary ingredients gathered Let’s get to work. The process is quite simple and consists of these steps:

  • We connect the flash memory to the Mac and change the name to “FLASH”, without the quotes.
  • We open the Terminal app, which we can search using Spotlight.
  • We copy and paste the appropriate command depending on the beta version that we have downloaded.
  • For macOS Big Sur in public beta:
    sudo / Applications / Install macOS Big Sur –volume / Volumes / FLASH –nointeraction

    For macOS Big Sur in developer beta:
    sudo / Applications / Install macOS 11 –volume / Volumes / FLASH –nointeraction

  • We press Enter (↩︎).
  • We write the password of our Mac and press Enter again.
  • The process can last up to 20 minutes depending on the speed of the computer we are using. We will see several process indicators in the same terminal and when it is completed we will see “Done” in the last line. And just like that, we’ve created a bootable Big Sur installer.

    And now that?

    Now we can proceed to the installation of Big Sur from scratch. To do so we simply turn off the computer, we connect the flash memory and turn it on while pressing the option key (⌥). When the menu to choose appears, we select the Big Sur installer.

    Remember that some Macs with the T2 chip need us to enable this external boot option. To do so, we simply turn off the Mac and turn it on by pressing Command (⌘) + R. Then, in the Utilities menu we choose Startup Security Utility and we will mark the option * Allow startup from external support. After restarting the computer, we will be able to use our installer on the Mac.

    Let’s keep in mind that for the installation to be from scratch it is necessary to erase the content of the entire hard drive, the process is very easy, as our colleague Miguel López explains in the following video:

    And that simple. We have created a bootable macOS Big Sur installer and have seen how to use it to create a clean system installation. A resource that forces us to reinstall applications and settings after the process, but that can improve errors and the general performance of the computer.