Apple quietly fixes a bug that let users install macOS Big Sur on Macs without enough space

Macos Big Sur Craig Wwdc (Image credit: Apple)

What you need to know

Apple has released a new update that prevents macOS Big Sur from being installed on devices without enough storage space.
The fix doesn't help users who are already stuck with a half-installed update, though.

Apple has released an update that should prevent users from being able to begin a macOS Big Sur installation even when their Mac doesn't have enough storage space.

As reported by 9to5Mac and Mr. Macintosh, Apple has quietly released a new build of macOS Big Sur 11.2.1 (20D75) that prevents installations when insufficient space is available. However, it isn't going to help those who are already having issues. Those who found they didn't have enough space to complete an update are left with a Mac that refuses to boot.

When you start the macOS Big Sur upgrade, the installer should first check to make sure your Mac has enough free space available. If the installer finds that you do not have enough free space for the upgrade, it will stop and not let you continue. You should see a pop up message showing you how much space is needed before you can attempt the upgrade again. This free space check is NOT working. The upgrade will start even if you only have 1% of free space left and will fail. Your hard drive is now 100% full and the installer is now stuck in a boot loop attempting to finish the install.

macOS Big Sur 11.2.1 (20D75) full installer is now available for download.

I've confirmed the new installer now checks for free space properly.

This was a serious problem, and I'm glad users will no longer get caught by this issue. https://t.co/dYSuRjdd4p pic.twitter.com/ILxoKfhORnmacOS Big Sur 11.2.1 (20D75) full installer is now available for download.

I've confirmed the new installer now checks for free space properly.

This was a serious problem, and I'm glad users will no longer get caught by this issue. https://t.co/dYSuRjdd4p pic.twitter.com/ILxoKfhORn— Mr. Macintosh (@ClassicII_MrMac) February 15, 2021 February 15, 2021

Apple says upgrading to macOS Big Sur for the first time requires at least 35.5 GB of available storage — and this doesn't include the 13 GB macOS Big Sur installer. Unfortunately, even if your Mac does not have 35.5 GB of storage available, macOS will try to install the Big Sur update, and that's when users may lose all their data.

If you're stuck in that position you can follow the steps outlined by Mr. Macintosh. Good luck!

Oliver Haslam has written about Apple and the wider technology business for more than a decade with bylines on How-To Geek, PC Mag, iDownloadBlog, and many more. He has also been published in print for Macworld, including cover stories. At iMore, Oliver is involved in daily news coverage and, not being short of opinions, has been known to 'explain' those thoughts in more detail, too. Having grown up using PCs and spending far too much money on graphics card and flashy RAM, Oliver switched to the Mac with a G5 iMac and hasn't looked back. Since then he's seen the growth of the smartphone world, backed by iPhone, and new product categories come and go. Current expertise includes iOS, macOS, streaming services, and pretty much anything that has a battery or plugs into a wall. Oliver also covers mobile gaming for iMore, with Apple Arcade a particular focus. He's been gaming since the Atari 2600 days and still struggles to comprehend the fact he can play console quality titles on his pocket computer.