How to see who is logged on to many workstations?

Question

Before I go to work creating my own I would like to find an existing system to do the following:

• Provide a concise list of users logged on to any of the workstations
• Show workstation host name, IP, and user name
• Data should update frequently or when there is a change
• Web or console interface
• Run on a Debian/Squeeze machine
• Free/Libre software

Situation:

• 60 Ubuntu 10.04 workstations spread over 3 sites
• Sites connected by 20Mbps WAN
• one server at each site running NFS and LDAP
• Workstations configured to authenticate users via LDAP and auto mount homes from local NFS server
• Users can log on to any machine they want

Answer 1

There isn't anything that does all of that but rwhod gets you started.

Run rwhod on all nodes. On any one node run rwho to see who's logged in on all nodes.

Answer 2

Perhaps some finger daemon already provides some of your requirements.

On my Ubuntu system there are several available:

$ apt-cache search finger --names-only
finger - user information lookup program
cfingerd - configurable finger daemon
efingerd - Another finger daemon for unix capable of fine-tuning your output.
finger-ldap - Finger for machines that authenticate against LDAP
fingerd - remote user information server
xfingerd - BSD-like finger daemon with qmail support

Some finger commands provide also the possibility to query machine information.

For example on a Solaris network where finger is setup:

$ finger juser
Login name: juser                    In real life: Joe User
Directory: /home/juser               Shell: /bin/bash
Login             Name          Idle TTY     Host        When   Where
juser Joe User                  0:03 1   machineA     Wed 20:18 >example.org
juser Joe User                  0:20 17  machineB     Wed 20:11 >example.net
No mail.
Plan:
Do this and that ...

Or to get a list of free machines:

$ finger .free
39 hosts free, 5 not responding.
Free hosts are machineC (idle 2 days, 12:24:49), machineD (idle  3:03:50), 
machineE (idle 1 day,  6:22:53), ...