How do you know who's logged in to your Linux/Unix server?
It's actually pretty simple:
Go to the terminal and type "w" or "who" followed by <return> - then you will get a list of active users and the IP address they had at login.
If you want to know who has been logged in during a given period, you can use
'last' in the terminal.
$ last -s "-3 weeks"
will give you an overview of users who have been logged in for the past 3 weeks.
$history
will give you a summary of the most recently executed commands. You can then choose to pass the output on to 'less' or 'grep' to search more in-depth.
$ history | grep -i "ssh"
gives you an overview of used ssh commands
You can always look in the man(ual) to see what other options you have with a command.
$ man who
Have a nice weekend :-)