Cannot Open Display localhost:0.0, but can open :0.0

I did a
  > netstat -an | grep 6000

and nothing showed up, so it sounds like you're right. How do I setup to listen on port 6000?

Are you sure you need that ???
It is possible, but explain what advantages you will get etc, maybe there is more secure solution available.

It is a secure environment (not on the net), so we don't really care about security. I'm mostly looking at simplicity. More than that, we don't really need to throw X around in the final app, just for testing components.

So, I don't care if the solution is a /etc/X11/xdm or gdm config file, if it is an xauth list kind of solution, or something else that is simple. :)

So what is the problem ???

I can't throw an X window to another machine--that's the problem. I don't care how I solve it as long as it can be solved (that was the point of the 7/29/2005 posting)--sorry if that wasn't clear. What I don't care about is the security issue as the machines are in a closed environment. But we still have the problem that we  can't display an X window (like xclock) from Sys1 onto the Sys0 display.

The latest thing someone tried, but I have fully verified it working or not, is to run on machine called "Sys0":

     iptables -I INPUT -p tcp --dport 6000 -j ACCEPT

or try to put this kind of statements into /etc/sysconfig/iptables_config. The firewall is disabled, so I didn't expect to have to do this, but running nmap and netstat it is clear that the machines (none of them) are listening to port 6000. I'm no expert here (obviously!) so I don't know why the machines are not listening.

Hope that clarifies the situation...

The problem is not with firewall currently.
You have to enable Xserver to listen on tcp.
Probably /etc/X11/Xservers, or some other file named Xservers has obvious configuration directive "-nolisten tcp" which has to be removed before Xserver restarted.

(Pretty much what Andrew is saying, but perhaps a bit more verbose:-):

I'm "guessing" that the X server on Sys0 gets started with the "-nolisten <port(s)>" or "-nolisten tcp" flag, perhaps in /etc/X11/xdm/Xservers (xdm and kdm) or /etc/X11/gdm/gdm.conf (in the [servers] section (which might point on to "subsection"). This is not something that can be set in XF86Configure or xorg.conf.

This would definitely have the effect you describe, since DISPLAY=:0 would use unix domain sockets (local FIFOs) while DISPLAY=localhost:0 would use network sockets for the same communication.

-- Glenn

Oh, incidentally, when you've found where it's set, just remove the "-nolisten ..." parameter and restart the display manager... Perhaps simplest and safest via a reboot.... and you're done.

-- Glenn

What you both are saying makes sense (and I have looked previously for the nolisten option anywhere) and haven't found it. I wonder if "nolisten" is a default condition in X for this kernel? Or is there some other Xauthority file that this could be in?

Thanks again--sounds like we're all on the same page, but I still have to find who is closing the port or forcing "nolisten".

Dean

This is my entire Xservers file from /etc/X11/xdm/Xservers:

# $Xorg: Xserv.ws.cpp,v 1.3 2000/08/17 19:54:17 cpqbld Exp $
#
# Xservers file, workstation prototype
#
# This file should contain an entry to start the server on the
# local display; if you have more than one display (not screen),
# you can add entries to the list (one per line).  If you also
# have some X terminals connected which do not support XDMCP,
# you can add them here as well.  Each X terminal line should
# look like:
#   XTerminalName:0 foreign
#
:0 local /usr/X11R6/bin/X


-----------------------------------------------

Here is the gdm.conf file (/etc/X11/gdm/gdm.conf) without comment lines:

[daemon]
AutomaticLoginEnable=false
AutomaticLogin=

TimedLoginEnable=false
TimedLogin=
TimedLoginDelay=30

Greeter=/usr/bin/gdmgreeter

DefaultPath=/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin
RootPath=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin


User=gdm
Group=gdm
LogDir=/var/log/gdm
PidFile=/var/run/gdm.pid
PostLoginScriptDir=/etc/X11/gdm/PostLogin/
PreSessionScriptDir=/etc/X11/gdm/PreSession/
PostSessionScriptDir=/etc/X11/gdm/PostSession/
DisplayInitDir=/etc/X11/gdm/Init
XKeepsCrashing=/etc/X11/gdm/XKeepsCrashing
ServAuthDir=/var/gdm
BaseXsession=/etc/X11/xdm/Xsession
DefaultSession=default.desktop
UserAuthDir=
UserAuthFBDir=/tmp
UserAuthFile=.Xauthority
StandardXServer=/usr/X11R6/bin/X
Xnest=/usr/X11R6/bin/Xnest -audit 0 -name Xnest

[security]
AllowRoot=true
AllowRemoteRoot=true
AllowRemoteAutoLogin=false
RelaxPermissions=0
RetryDelay=1
UserMaxFile=65536

[xdmcp]
Enable=true
HonorIndirect=true
Willing=/etc/X11/gdm/Xwilling

[gui]
GtkRC=/usr/share/themes/Bluecurve/gtk-2.0/gtkrc

[greeter]
TitleBar=false
ConfigAvailable=false
Browser=false
MinimalUID=500
Logo=
BackgroundColor=#20305a
ShowGnomeFailsafeSession=false
ShowLastSession=false
GraphicalTheme=Bluecurve
GraphicalThemeDir=/usr/share/gdm/themes/

[chooser]
HostImageDir=/usr/share/hosts/
Hosts=

[debug]
Enable=true

[servers]
0=Standard


[server-Standard]
name=Standard server
command=/usr/X11R6/bin/X -audit 0
flexible=true

[server-Terminal]
name=Terminal server
command=/usr/X11R6/bin/X -audit 0 -terminate
flexible=false
handled=false

[server-Chooser]
name=Chooser server
command=/usr/X11R6/bin/X -audit 0
flexible=false
chooser=true

Newer kdm uses own config file (3.4+). This has to be noted for example for Mandriva(or -ake)

Interesting...I hadn't thought to look for kdm config files in particular. I didn't know where to find them, so did a quick Vivisimo search and found that they are in /usr/share/config/kdm, most of its files linking to /etc/X11/xdm. If found the file kdmrc which looks like it's the same format as xdm-config. I found settings in kdmrc there that said:

[Xdmcp]
# Whether KDM should listen to XDMCP requests. Default is true.
Enable=false

and changed it to
Enable=true

I'll let you know how it works once I'm allow to interrupt development to try it out.

Dean

xdmcp is network listener, so you can connect from anywhere in network and get login display (subject to Xaccess restrictions)

So what is the recommendation? I did try turning Enable to true in the 'kdmrc" file to no avail. If the display is using Gnome, will kdmrc be used at all anyway?
As you can see from the gdm.conf file, -nolisten is not set. What else could it be? Or, alternatively, could you post or know where I can find a set of gdm.conf / xdm config files that will allow tcp:6000 listening?

kdm does not apply to Fedora
gdm has to be configured
so
what does natstat -an | grep 6000 show ???

netstat -an | grep 6000

Oh and incidentally, Andrew is quite correct that XDMCP is _not_ needed, unless you want Sys0s gdm to be able to MANAGE "foreign" displays. Not really what we're aiming at here;-/

-- Glenn

.... just to be clear:
The sole function of the DisallowTCP setting is to "automagically" add "-nolisten tcp" to any X server commandline handled by gdm _except_ those handling XDMCP things (-query and -indirect basically).

-- Glenn

netstat -an | grep 6000 shows nothing. Thanks for the info on XDMCP--that eliminates those options.  So, if something is happening "automagically" (I love that term), how can I not so automagically Allow TCP?

Also, in case it is of interest,

[root@Sys0 xdm]# nmap -sT localhost

Starting nmap 3.48 ( http://www.insecure.org/nmap/ ) at 2005-08-04 11:28 AST
Interesting ports on localhost.localdomain (127.0.0.1):
(The 1648 ports scanned but not shown below are in state: closed)
PORT      STATE SERVICE
22/tcp    open  ssh
25/tcp    open  smtp
111/tcp   open  rpcbind
513/tcp   open  login
514/tcp   open  shell
631/tcp   open  ipp
783/tcp   open  hp-alarm-mgr
32774/tcp open  sometimes-rpc11
32775/tcp open  sometimes-rpc13

Nmap run completed -- 1 IP address (1 host up) scanned in 0.363 seconds
[root@Sys0 xdm]# nmap -sT 204.100.186.247

Starting nmap 3.48 ( http://www.insecure.org/nmap/ ) at 2005-08-04 11:29 AST
Interesting ports on Sys0 (204.100.186.247):
(The 1652 ports scanned but not shown below are in state: closed)
PORT      STATE SERVICE
22/tcp    open  ssh
111/tcp   open  rpcbind
513/tcp   open  login
514/tcp   open  shell
32774/tcp open  sometimes-rpc11

Nmap run completed -- 1 IP address (1 host up) scanned in 0.363 seconds

Do I just put in

DisallowTCP=false

in gdm.conf?

Does it matter where?

Look for yourself:
http://yippi.hypermall.com/gdm/gdm-documentation/x241.html

telinit sequence on terminal that does not run X ... for example gnu screen or one accessed by Ctrl-Alt-F1 keypress

FYI: whenever I tried to make the change (DisallowTCP=false) and then reboot the server (via ctr-alt-backspace), it didn't take. Rebooting did.

As if I did non knew....