mac first aid volume could not be unmounted

If you haven’t tried this type of fix yet, follow the instructions below: This particular issue is confirmed to work on a wide variety of macOS versions including ElCapitan, Sierra, High Sierra, and Mojave. Several affected users have confirmed that they’ve been able to fix the issue by opening the built-in Terminal app and running a command capable of repairing the drive remotely. If you’re encountering this issue while trying to run the First Aid utility on the affected drive, you should attempt to do the repairs via the Terminal app. Now that you know every potential fix that might trigger this error code, here’s a list of methods that might allow you to fix this issue: Method 1: Repairing the Disk via the Terminal App If it’s not, take it to a certified technician for investigations. If your Mac is still under warranty, send it in for a replacement. Failing disk drive – If you’re encountering this particular issue with a native OWC drive and none of the recovery options presented above prove to be effective, you should seriously consider investigating a hardware issue.Corrupted macOS startup sequence – If this is a debilitating issue that no longer allows your macOS computer to boot up, you should attempt to fix the corrupted booting sequence by using the Recovery Menu to reinstall all your macOS files.In this case, you can mount a previously created Machine Backup that’s either stored on a physical drive or on the crowd. Corrupted macOS files – As some affected users have been reported, you might expect to see this error due to some kind of corrupted OS files that end up affecting the First Aid utility.If this scenario is applicable, you should be able to fix this issue by trying to repair the disk via the Terminal app.

A problem with the First Aid Utility interface – As it turns out, there’s a weird problem that seems to affect ElCapitan and High Sierra versions of macOS in which the First Aid utility acts up when forced to inspect a secondary drive.

Mac first aid volume could not be unmounted