who - show who is logged on
To print who command output without options $ who
To print the heading of the columns displayed $ who -H
To print the login names and total number of logged on users $ who -q
To show only hostname and user associated with stdin $ who -m
To add user's message status as +, - or ? $ who -T
To view the time of last system boot $ who -b
To check the current runlevel $ who -r
To print dead processes $ who -d
To see active processes spawned by init $ who -p
To print last system clock change $ who -t
To list users logged in $ who -u
To print same as -b -d --login -p -r -t -T -u $ who -a
regards, T.Dhanasekar