Apple fixed a particular problem with macOS Big Sur that previously allowed users to install the operating system update even if they didn’t have enough space on their Macs to do it. As you’d expect, installing an update when you don’t have the space leads to all sorts of system problems.
If you have a macOS Big Sur installer on your system, make sure you have updated your Mac and all of its apps to the latest version of the operating system. Next, confirm which version of Big Sur InstallAssistant you have by following the instructions HereIn case it’s still sitting around on your Mac waiting to be run. If you’re not using 11.2.1 (20D75), remove it and reinstall the macOS Big Sur update package.
Once you do, you will no longer be able to install macOS Big Sur if you run out of space on your hard drive. If you don’t, you have a few options for freeing up space a full backup Your system. Once you know where you usually keep some of your gigantic files (e.g. your Downloads folder), start there. Delete what you no longer need and move the rest after Cloud or external storage.
If you need help, use your Mac Memory management App to move your files, photos and messages to iCloud; Remove movies and TV shows from your Mac that you’ve already seen. automatically clear out your trash; and identify files that you no longer need to store on your Mac.
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Or use the tool to manually search for files that are taking up a lot of space. Just click the different categories in the sidebar – Applications, Documents, iCloud Drive, Messages, and Trash – to see the different files that are taking up all of your hard drive space.
If you’ve already tried installing macOS Big Sur but ran out of disk space and the update messed up your system, you’ve done it a couple of options to remove and save your data. They’re a little verbose, but they should be within reach of most people. With FileVault enabled, you’ll either need to install and boot from macOS Mojave to external storage to free up space on your Mac’s primary hard drive, or use a second Mac in Target Disk Mode to mount your hard drive and free up space for the installation of macOS Big Sur is complete.
Otherwise, you can use the Terminal app in macOS Recovery to delete files or use either of the two tricks above to free up space and complete the Big Sur installation.
For this reason, I always recommend backing up your data before performing a major operating system update. If you don’t need anything on your Mac’s hard drive – because you’ve already backed everything up – troubleshooting the problem becomes a lot easier. Just start your Mac Recovery modeErase your entire hard drive and reinstall macOS. You can then use Migration Assistant to get all of your files back, even if you figure out how to free up enough space on your system to install macOS Big Sur.
