who - show who is logged on
Display user login name, user’s terminal, time of login and remote host:
who
Display the heading of the columns:
who -H
Display login names and total number of logged on users:
who -q
Display only the hostname and user associated with stdin:
who -m
Display message status of each user:
who -T
Display the time of last system boot:
who -b
Display the current runlevel:
who -r
Display dead processes:
who -d
Display active processes spawned by init:
who -p
Display all information:
who -a