How to VNC a client's login screen (KDM, GDM, LoghtDM, etc.)?

Asked by Laércio de Sousa on 2012-08-21

Reading the Epoptes' changelog, I've found some mentions to VNC'ing the client's login screen (KDM, GDM, etc.), so I could remotely log my clients on.

Does it work out-of-the-box? Is there some configuration needed?

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Alkis Georgopoulos (alkisg) said : #1

I works out of the box
(unless if epoptes-client isn't properly installed).

Olivier Korn (olivier-korn) said : #2

Maybe you should explain how to to properly install epoptes-client, because I can't use this feature.

Client are working perfectly after login, I can also start computers remotely (WOL), and so on.

BUT I can't manage to access computers before somebody has logged in, or between two sessions (when first user has closed his/her session).

Would you be kind enough to explain what I am missing or what I need to tell you in order to sort it out?

Alkis Georgopoulos (alkisg) said : #3

Before login, you should be seeing little red monitor icons like those:
From there, you can select to assist the user from the epoptes menus (i.e. take control with x11vnc).

If you don't, it's either a misconfiguration or a bug.
In that case, please mention the following, for both the server and the clients:
distro+version, DE, if you're using LTSP or not (netbooted thin clients),
and the output of `epoptes`, if you run it on a terminal on the server,
and `sudo epoptes-client`, if you run it from vt1 (alt+ctrl+f1) on a client.

For example, a possible cause could be that your networking is configured to work only after login (network manager user connections instead of system connections).

Olivier Korn (olivier-korn) said : #4

This is what I see:
The client host is up and running, freshly started (I can "ping" it).

Server is Ubuntu 12.04 LTS.
Client is Edubuntu 12.04 LTS.
LTSP is not used.

Running `epoptes` on the server gives this message: "Got clients: None".
Running `sudo epoptes-client` on the client doesn't do anything visible (apart from asking for user's password of course). Afterwards, server is still unable to contact client.

I believe networking is configured to work at any time, since I can ping client host from server host.

LTSP is not used. For this reason, if I read well the script, /etc/init.d/epoptes-client exists early with code 0. Maybe this is the cause?

Alkis Georgopoulos (alkisg) said : #5

The problem most probably is that you have epoptes installed on the clients.
By design, the "system" epoptes-client, the one that you tried to launch with sudo, refuses to run on the epoptes "server", because that's where usually the teacher works, and he usually doesn't want other people controlling his computer.

Check lines 173 and below of /usr/sbin/epoptes-client:
# We don't want the epoptes-client system service running on the epoptes server
if ( [ $UID -eq 0 ] && [ $TYPE = "standalone" ] && [ -x /usr/bin/epoptes ] ) ||
    exit 0

So if that's actually the cause, the solution is to remove the epoptes package from the clients, but keep the epoptes-client package.

Olivier Korn (olivier-korn) said : #6

This was indeed the problem. Thank you for your help and your kindness.

Wouldn't it be possible to mark each package as mutually exclusive of the other? This way, it won't be possible to install both of them?

I can't remember having installed the serveur (nor the client) on Edubuntu 12.04. Were they both installed by default?

Eventually, was this documented somewhere? Maybe the script itself could output a warning for us to have something to read in client logs.

Thank you very much, anyway.

(For my records: to install properly epoptes-client means also to uninstall properly epoptes).

Alkis Georgopoulos (alkisg) said : #7

> Wouldn't it be possible to mark each package as mutually exclusive of the other?
> This way, it won't be possible to install both of them?

There are some cases, notable LTSP servers, where we do want both of them.

> Eventually, was this documented somewhere?

Besides the comment in the source code, no, and while Edubuntu student PCs shouldn't have epoptes install, the whole case does deserve a bit more thinking, either user messages, logs, or some more clever handling. In some of the next versions... :)

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