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I have just found that my latest kubuntu comes preconfigured with the following:

in directory /etc/X11/xinit there is xserverrc


exec /usr/bin/X -nolisten tcp "$@"

But the -nolisten tcp arguments are nowhere to be found on the help for X (man X) and we have the feeling this is causing some problems with our tools. They say cannot connect to DISPLAY, etc...

Have you ever seen this argument? What might happen if I remove the -nolisten tcp (ie.. will it open a normal TCP connection?)

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up vote 2 down vote accepted

The option is there to avoid the security problems inherent in xhost +IP. Removing it will cause no problems but can be a security risk, it's up to you. As far as I can tell the option causes the X server not to listen for incoming connections.

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The documentation for the generic X server options may be found in man Xserver:

    -nolisten trans-type
                disables a transport type.  For example, TCP/IP connections can
                be disabled with -nolisten tcp.   This  option  may  be  issued
                multiple  times  to  disable  listening  to different transport

As mentioned this option disables any TCP/IP based access to the X server - which is what you generally want as X11 security is not particularly strong. It is better to tunnel X11 over ssh if you need remote applications to display on your X server (e.g. ssh -XY remote_host xeyes Note: the -X option enables X11 forwarding, and -Y enables trusted X11 forwarding - which is not subject to the X11 SECURITY extension controls.)

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