Is Single-user Mode Dead?
Even with Recovery Mode available, there have still been some reasons for wanting to enter SUM. One of them has been to run command tools to check memory for faults, as in SUM the system takes as little memory as possible, allowing you to run checks on all the rest. Sometimes
fsckrun from SUM could fix problems which Disk Utility in Recovery Mode couldn’t.[…]
The biggest problem comes with Macs equipped with a T2 chip, and its Secure Boot. If it were available, a traditional SUM would bypass Secure Boot, so it isn’t allowed if your Mac has a T2 chip: Command-R will take you to Recovery, and that’s as close as your Mac can get, unless you disable Secure Boot by setting the Startup Security Utility to No Security. And you have to do that in Recovery anyway.
