how to monitor remote sessions ?

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Hello
We have a linux server, other users could establish connection through SSH to the server (say other admins in network) .
I like to know what are they doing across SSH and want to know what exactly are they doing on the server .
Do you have a reliable solution for this problem ?
One of my friends introduced Wireshark to me, can wireshark do the ssh session and remote connection monitoring for me ?
Is it possible in a reliable way ?

please give your ideas .
thnx

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Sorry I mean tripwire ...