iXvnc patch for VNC=20 X-Server (Xvnc)

Warning 1: this patch is no longer required = because=20 is included in the original sources of the current releases.=20
Warning 2: this option is usefull only if = you want=20 to use XDM to start the user sessions (otherwise you get just a gray = screen) ,=20 check the xdm man pages.=20

Goal

I wasn't able to convince my users to start their own Xvnc before = using the=20 viewer, so it must start on demand. With this patch you'll be able to = use=20 inetd to launch Xvncs as clients connect.

To achieve this we've made some minor changes for Xvnc to support the = new=20 -inetd command line option.
If -inetd option is not = used=20 then Xvnc should work as usual and can be started by the vncserver = perl=20 script provided with Xvnc.

This patch was designed to minimise changes to the original source = code,=20 currently only two files are patched (init.c and sockets.c).

Features (-inetd option):

• Doesn't listen for connections of any kind (http included).=20
• Receives a connected socket from inetd and uses these client = connection.=20
• Finds a free display number and uses it.=20
• If connection is gone then terminate Xvnc=20
• Logging to /usr/adm/Xddmsgs

How to:

Suppose you have the Xvnc source. Would be better to compile it first = (just=20 to be sure its ok).

Get the appropriate patch file (check "Change Log"):

• Go to vnc directory in your source tree = (.../Xvnc/programs/Xserver/hw/vnc)=20

• Untar the TGZ file(*)
  WARNING !!!! - this will overwrite some = files, if=20 you which backup first.=20
• Rebuild (and that's it)

(*) Now you can also use the patch versions, untar the=20 ixvncXX.patch.tgz file and then, in the vnc directory, use the patch = command=20 (patch < ixvncXX.patch).

Installing/Using

New entries are required in /etc/services and = /etc/inetd.conf.=20

/etc/services

In this file the new services must be defined: service-name=20 port-number/protocol. In our case we want to give users several = options=20 about geometry's and depths so my file has this lines (you may want just = one):

vnc-640x480x8	5950/tcp
vnc-800x600x8	5951/tcp
vnc-800x600x16	5952/tcp

On the client side this means displays :50 :51 and :52. The display = number=20 used by Xvnc won't be the same; with -inetd option an available = display=20 number will be searched and used.

/etc/inetd.conf

In this file you must add the lines to launch Xvnc, in my case the = basic=20 options are:

vnc-640x480x8	stream tcp nowait =
nobody /usr/local/bin/Xvnc Xvnc -inetd -broadcast -once -geometry =
640x480 -depth 8
vnc-800x600x8	stream tcp nowait nobody /usr/local/bin/Xvnc Xvnc -inetd =
-broadcast -once -geometry 800x600 -depth 8
vnc-800x600x16	stream tcp nowait nobody /usr/local/bin/Xvnc Xvnc -inetd =
-broadcast -once -geometry 800x600 -depth 16

You must add other command line options required for your local=20 configuration, namely -fp.

As you can see Xvnc will run as nobody (check if that's ok for = your=20 local configuration). Any number of clients may connect to :50 :51 or = :52, inetd=20 will launch a Xvnc for each. You may use any Xvnc options (some systems = may=20 restrict the number of command args in inetd.conf) but don't forget = -inetd=20 -broadcast -once, of course -broadcast can be replaced by = -query {hostname}.

After changing these files you must send a HUP signal to inetd = process (or=20 reboot).

Other points

• To support the Java client, just serve the applet from a standard = httpd=20 (must be on the same machine as Xvnc) directed to the = appropriate=20 host/port. Even if one is not required, the VNC viewer applet always = asks for=20 a vnc password, changing this requires major rewriting of the applet. = Anyone=20 interested?=20
• As pointed out by Laurent Bardi allowing or denying IP clients = access it's=20 now easy. Just check "man tcpd".=20
• By using VNC this way some interesting features are lost, namely = being=20 able to keep Xvnc server running while connecting and disconnecting as = you=20 need and sharing the desktop. Adam Nevins said keeping those features = would be=20 nice, to be able to do so, something like a self-generated password = would be=20 required. Other ideas?

Change Log

BUGS and Problems

• Because with iXvnc display numbers will be locked without using = the=20 corresponding vnc ports, if you also use the vncserver script you may = expect=20 it to issue warning messages about this fact.=20
• Before executing Xvnc inetd closes handles 0, 1 and 2 and then = copies the=20 connected socket to these handles. This means stdin, stdout and stderr = are all=20 directed to the tcp connection.
  Before version 3a iXvnc = patch=20 removes all vnc logs and error reporting that are normally directed to = stderr.=20 However it does not remove the X-Server error logs. If there is an = error in=20 X-server stuff the error message is written to stderr and will produce = fatal=20 effects. If you get something like "invalid protocol", "invalid rfb = server" or=20 "unknown message" on the vncviewer this probably means some error has = occurred=20 and an error message was written on stderr. If this happens when you = connect=20 you can get the error message by using a telnet client directed to the = vnc=20 port.=20
• This patch searches for a free display the same way the vncserver = perl=20 script does, however that isn't correct. The lock file should be = created on=20 the search and not when the X server starts afterwards (when two or = more=20 searches take place at the same time it's easy to guess what may = happen).=20
• Gray screen this is the most reported problem, however it's = not a=20 VNC problem. If you get a gray screen and nothing else then you = probably don't=20 have a XDM server running on your network. You should setup one, when = this is=20 done, you will get a nice login window on your gray screen. Check xdm = man=20 pages (on the unix shell run: man xdm). Recente desktop environements = carry=20 specific XDM servers, like KDM for KDE and GDM for GNOME.

andre@dei.isep.ipp.pt
http://www.dei.isep.ipp.pt/~an= dre
Departamento=20 de Engenharia Inform=E1tica (DEI)
Instituto Superior de = Engenharia=20 do Porto (ISEP)
Instituto = Polit=E9cnico=20 do Porto (IPP)

Rua Dr. = Bernardino de=20 Almeida 431
P-4200-072 PORTO, Portugal =

LinuxSupport.org.uk was designed and built by Paul Vigay. In Pauls absence this site has now been taken over and updated by Bob Ruskin. Latest Updates | Copyright | Disclaimer | Privacy policy