This is a following article about Unix commands. Here you will find a few others. This series concerns user connected to a computer or a server.

Who is connected to your computer :

$ who

For more details about the connected userss

$ w

To know who is connected localy:
$ users

To send a message to a user:
$ write use_name
Control+c to stop.

To know for how long the computer or server is booted:
$ uptime

Related articles:

• Unix Command Terminal OS X (lesson 1)