macOS Big Sur Bug Could Lead to Data Loss
Shortly said, the bug stems from the macOS Big Sur installer not checking whether the machine has the required free space for an upgrade to occur flawlessly.
The macOS issue has been analyzed in depth by Mr. Macintosh.
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. This leaves you unable access your data!
How can this be fixed? Mr. Macintosh provided a fix, but the good news is that Apple released an updated macOS Big Sur 11.2.1 installer (20D75) that checks for the available free space.
The issue highlights the importance of having a backup of your data. A good advice is to always check the system requirements prior to upgrading. As it turns out, relying on the installer may not be a good idea.
This is not the first time macOS experiences issues that could cause severe data loss. “The 2019-001 Security update issue was close to this one. If you installed the 2019-001 Security Update and the Mac was encrypted, the user could be locked out,” Mr. Macintosh pointed out.
Earlier this month, Apple released a patch for the critical sudo bug (also affecting Linux) in macOS Big Sur, Catalina, and Mojave. The flaw could enable unauthenticated local users to obtain root-level privileges on the affected system.