How to Fix MacOS Big Sur Installation If You’re Out of Space
Apple has fixed a specific issue with macOS Big Sur that previously allowed people to install an OS update even if they didn’t have enough space for it on their Macs. As you would expect, installing an update when you are out of space causes all sorts of system issues.
If you have macOS Big Sur Installer installed on your system, check if you’ve updated your Mac and all of its apps to the latest OS version. Then confirm which version of Big Sur InstallAssistant you have installed by following the instructions here , in case it is still sitting on your Mac waiting to launch. If you are not using 11.2.1 (20D75), uninstall it and reinstall macOS Big Sur Service Pack.
Once you’ve done that, you won’t be able to install macOS Big Sur if you don’t have enough hard drive space to do so. If you don’t, you have several ways to free up space. Start by creating a complete backup of your system. If you know where you usually store some of your giant files (like the Downloads folder), start there; delete what you no longer need, and move the rest to the cloud or external storage .
If you need help, use the Mac storage app to move files, photos, and messages to iCloud; delete movies and TV shows you’ve already watched from your Mac; automatically empty the basket; and identify the files you no longer need to store on your Mac.
Or use a tool to manually scan files that take up a lot of space. Just click on the different categories in the sidebar – Apps, Documents, iCloud Drive, Messages, and Trash – to see how different files are taking up all of that hard drive space.
If you’ve already tried installing macOS Big Sur but ran out of space and the update crashed your system, you have several options to remove it and save your data. They are a little verbose, but should be achievable for most people. If you have FileVault enabled, you’ll either need to install and boot 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 the drive and free up space to complete the macOS installation. Big Sur.
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.
I always recommend backing up your data before doing a major OS upgrade for this very reason. When you don’t need anything on your Mac’s hard drive because you’ve already backed up it all, fixing the problem becomes much easier. Just boot into your Mac’s recovery mode , erase your entire hard drive, and reinstall macOS. You can then use Migration Assistant to get all your files back, even when you’re figuring out how to free up enough space on your system to install macOS Big Sur.