While current Retina lines of Macs tend to run on Intel iGPUs and AMD Radeons, previous generation was primarily delivered with Nvidia’s. It shouldn’t come as a surprise then if Nvidia is not opting Mac in to their extended support. If you are experiencing the issue I am describing, I can only hope you have a backup.
The symptom is innocuously simple. On boot, the loading bar progresses just fine, but it will not actually boot although the bar is full. If so, you will need to do some digging if your Mac is actually affected.
To boot in Verbose mode: press CMD + V and hold
Verbose mode will display too many details at once, but what you need is at the end of it. If the last bit of logs show following lines, you are affected:
IOConsoleUsers: gIOScreenLockState 3, hs 0, bs 0, now 0, sm 0x0
In order to remedy this issue, you will be installing a most updated version of macOS. If you already have a backup, make sure it’s up to date. If not, this is your chance to create a backup via safe mode or target disk mode. Also, if your network cannot handle recovery mode, you will need to create a new bootable USB drive.
- Boot from Internet Recovery Mode or a bootable USB drive.
- Open Disk Utility.
- Erase the “Macintosh HD” or any drive contains macOS.
- Quit Disk Utility. This will prompt OS Utility screen.
- Reinstall latest version of macOS.
This problem occurs when the provided Nvidia driver cannot communicate properly with the dGPU. Concurrently this issue is likely to arise when you are updating macOS, especially during the major OS upgrade. While this fix works as a patch job, ultimately I would suggest upgrading to a new computer within a year or two; macOS support lasts around 5-6 years and Nvidia’s Mac support is troublesome at best.