This tutorial shows you how to create a bootable macOS Big Sur Flash Drive so you can upgrade a Mac that doesn’t have a DVD drive.
Before we begin
You will need a USB Flash drive big enough to store the macOS Big Sur installer (13.57 GB). The USB Flash Drive will need to be wiped so don’t use a drive with existing data because you will lose it.
If you don’t have a spare USB Flash Drive, I recommend getting a
16 GB SanDisk Ultra Fit from Amazon* because they are fast, reliable and have a micro form factor. If you’re using a Mac that doesn’t contain USB ports, you might also need an
Apple USB-C to USB Adapter*.
You will also need to download the macOS Big Sur installer app to your Applications folder. You can do this using the command line by following the instructions in this tutorial.
Now that you’ve got your hands on a USB Flash Drive and a USB-C to USB Adapter, let’s copy the macOS installer to the drive and make it bootable by following the steps below.
- Connect the USB Flash Drive to your Mac, open the Disk Utility app, right click on the SanDisk USB Flash Drive then click Erase…
- Give the disk a name of SanDisk, select MacOS Extended (Journaled), GUID Partition Map then click Erase.
- When the Erase is complete, click Done.
- Click on the new SanDisk volume and you will see it has a mount point of /Volumes/SanDisk. Make a note of the mount point because we’ll use it in the command to create the installation media.
- Open the Terminal app and change into the directory containing the createinstallmedia utility.
cd /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources
- Run the createinstallmedia utility. Replace the volume with the mount point of your erased disk.
sudo ./createinstallmedia --volume /Volumes/Sandisk
- When asked to erase the volume, press y then return.
Ready to start.
To continue we need to erase the volume at /Volumes/Sandisk.
If you wish to continue type (Y) then press return: y
- Wait for the installer to be copied and the disk to be made bootable.
Erasing disk: 0%... 10%... 20%... 30%... 100%
Copying to disk: 0%... 10%... 20%... 30%... 40%... 50%... 60%... 70%... 80%... 90%... 100%
Making disk bootable...
Install media now available at "/Volumes/Install macOS Big Sur"
You now have a bootable macOS Big Sur USB Flash drive that you can use to upgrade your Mac or do a fresh install.