VNC Listening mode under Linux / vncconnect
Corné Beerse
cbeerse "at" lycos.nl
Thu May 27 17:46:01 2004
Bernd Lachner wrote:
> Hi,
>
> we want to use vnc in our school-network to make it possible to look at
> pupil-clients and to show the teachers-screen to all pupils.
> For Windows there is a destop-programm, but for Linux there is none (we
> found nothing).
From the remainder of your message I have the next impression (rephrase in
vnc-terms):
From M$Windows vncservers you can view the console (success with vncviewer
remote:0).
From Linux vncservers, you cannot view the console (no success with vncviewer
remote:0).
This is normal behavoure with the default packages.
>
> We looked at the manuals and know how to use vnc in "usual" mode: we can
> look at an other computer and control it. We also found the commands to
> start the client in listening-mode:
>
> vncviewer -listen :0
>
> Then on the server we executed the following command:
>
> vncconnect -display :0 hostname
>
> ... but nothing happend! No error-message!
Well, that's because on linux display number :0 is occupyed by the console which
has not vncserver attached to it. The default vncserver provides the next free
display number (:1, :2 and so on).
In a teacher-student relation where the teacher is the vncserver and the
students are the viewers, I would not want the students to view my console
session, I'd open a dedicated session for the instructive purpose. Hence point
the students to display :1 (or any other number). See my attached message to
have a static vnc-server on a unix machine that is just like the console session.
If it is for the teacher to peek on the students, then you would like to view
the console. There are various ways to do that:
There is a vnc-server module that hooks to some versions of XFree86. This would
be my preferred solution.
There is a vnc-server module that can be started from KDE. As far as I know it
hooks into the (KDE only?) windowmanager. `krfb` is a name that comes to mind.
There is a vnc-server that hooks into the framebuffer-device. If your machine
uses the framebuffer device, it can be an option.
>
> We are working on a Suse 9.1-System with kde 3.2.1, which has already
> started vncserver on display 0. We tested vnc and it is working.
Are you sure it is vnc at display :0? Most likely it is the Xserver that is
running at the console that is using display :0 which is most likely not
providing vncserver access.
>
> Do you have some examples, how to use the server and viewer in listening
> mode and how to connect from server to the client via vncconnect?
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Subject: Xvnc as a X-server (optionally replacing the console Xserver)
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X-Original-Date: Fri, 23 Jan 2004 10:52:57 +0100
Date: Fri, 23 Jan 2004 10:52:57 +0100
This is a description on how to use Xvnc as the Xserver. It is jet an other way
to create an always running vnc session on unix/linux. It is based on RedHat 9
but I think it can easy be moved to every unix that has a Xvnc binary.
My goal was to create a linux server that has a text console (for RedHat: as if
running in runlevel 3) but still has gdm available (actually running runlevel
5). Roughly, I just replaced the Xserver (XFree86 on linux) with Xvnc.
I first installed the vncserver packages from the distribution and start
`vncserver` at least once to have a vnc password file.
Then (sidestep) I installed
http://www.sourcecodecorner.com/articles/vnc/linux.asp. I don't expect it is
needed but for me it is the reason to run in runlevel 5 and not in runlevel 3.
The real work is in getting Xvnc used as an Xterminal that runs on the same
host. For GNOME (gdm) users: edit '/etc/X11/gdm/gdm.conf':
- disable VTAllocation (about line 104)
#VTAllocation=true
VTAllocation=false
- add server definitions (at the end, the double inserted lines are continuation
of the previous line, combine them.)
[server-ROOTVNC]
# vncsession, using vncpassword from root
name=ROOTVNC server
flexible=false
command=/usr/bin/Xvnc -geometry 800x600 -depth 8 -rfbwait 120000
-rfbauth /root/.vnc/passwd
[server-FREEVNC]
# vncsession, using no vncpassword
name=FREEVNC server
flexible=false
command=/usr/bin/Xvnc -geometry 800x600 -depth 8 -rfbwait 120000
-alwaysshared -dontdisconnect
- in the [servers] section, add and/or replace lines that indicate an Xserver:
# disable the X session on the console
#0=Standard
# use roots vncsession on :0
0=ROOTVNC
# use the free-access vncsession on :4
4=FREEVNC
Now restart gnome (or the entire machine) and see the console stays in its text
mode and there are 2 vnc sessions running: ONe at `vncviewer machine:0` that
uses the vncpassword of root and an other one at `vncviewer machine:4` that has
no vncpassword. All provide a login session.
To get the same setup with a KDE or XDM session, it is even simpler. Edit
'/etc/X11/xdm/Xservers': add the next lines (and comment out all others).
WRAPWARNING: each line is either comment or it starts with the same word as it
ends (:0 to :0 and :4 to :4).
# disable the X session on the console
#:0 local /usr/X11R6/bin/X
# vncsession :0, using vncpassword from root.
:0 ROOTVNC local /usr/bin/Xvnc -geometry 800x600 -depth 8 -rfbwait
120000 -rfbauth /root/.vnc/passwd :0
# vncsession :4, no vncpassword.
:4 FREEVNC local /usr/bin/Xvnc -geometry 800x600 -depth 8 -rfbwait
120000 -alwaysshared -dontdisconnect :4
Now restart the display manager (or the machine) and...
Detail, if you want to keep the X11 server on the console (not have the :0 vnc
session): you might need to add '-vt7' to the 'command=/usr/X11R6/bin/X -vt7' line.
If I can find some time, I might put this description on a website some time. If
others want to do so, please do. If I come acros any other system (HP-UX might
be the first) I might mail an update. Be free to test it on any other system.
Most likely you only need to update the Xservers file according the above
/etc/X11/xdm/Xservers description.
CBee
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