Mac OS Administration

PRAM Reset	⌘ + ⌥ + P + R	If your Mac is using a firmware password, it ignores this key combination or starts up from macOS Recovery
Recovery	Command (⌘)-R	built-in macOS Recovery system. Or use Option-Command-R or Shift-Option-Command-R to start up from macOS Recovery over the Internet. macOS Recovery installs different versions of macOS, depending on the key combination you use while starting up. If your Mac is using a firmware password, you're asked to enter the password.
Startup Manager	Option (⌥)	allows you to choose other startup disks or volumes, if available. If your Mac is using a firmware password, you're asked to enter the password.
Safe mode	Shift (⇧)
Hardware Test / Diagnostics	D	Option-D to start up from this utility over the Internet.
NetBoot server	N	Start up from a NetBoot server, if your Mac supports network startup volumes. To use the default boot image on the server, hold down Option-N instead.
single-user mode	Command-S	This key combination requires macOS High Sierra or earlier.
target disk mode	T
verbose mode	Command-V
Eject removable media	Eject (⏏) or F12 or mouse button or trackpad button

Startup Key Combinations