Some are fairly obvious. Specifically, I am referring to:
-h halt or power off after shutdown -H halt after shutdown (implies -h) -P power off after shutdown (implies -h)
Isn't halting or powering off kind of expected when you're shutting down? Aren't these redundant?
-c cancel a running shutdown
How on earth would you use this? In my experience, once a shutdown has begun, you don't get much opportunity to enter more commands until the machine is off.
-k only send warnings, don't shutdown
shutdown have an option that makes it not shut down?
What's the deal here? Does "shutdown" mean more than simply turning the machine off?