https://support.apple.com/en-us/HT201573

Start up your Mac in single-user mode or verbose mode

If you're an advanced user who is comfortable with UNIX, you can use single-user mode or verbose mode to help isolate issues related to startup.

Single-user mode

1. Turn on your Mac, then immediately press and hold Command-R to start up from macOS Recovery.
2. Select Disk Utility from the Utilities window, then click Continue.
3. From the Disk Utility sidebar, select the volume that you're using, then choose File > Mount from the menu bar. (If the volume is already mounted, this option is dimmed.) Then enter your administrator password when prompted.
4. Quit Disk Utility.
5. Choose Terminal from the Utilities menu in the menu bar.
6. You can now enter UNIX commands. When done, choose Apple () menu > Restart.
    

These steps replace the Command-S method, which doesn't work with the recommended settings on current Mac computers.

Verbose mode

1. Turn on your Mac, then immediately press and hold Command-V.
2. Continue holding the keys until you see white text on the screen.
   • If you're using FileVault, release the keys when you see the login window. Then log in to continue starting up in verbose mode.
   • If you're using a firmware password, you must turn off the password before you can start up in verbose mode.
3. You can now enter UNIX commands. To exit this mode and start up normally, type reboot, then press Return.

Published Date: September 24, 2018