Network communications typically use the "7 Layer Model". All X11 data between to processes (whether local or remote) flows through these 7 layers.
At one layer, a socket is an IP <address>:<port>
pair. TCP is a protocol used to send data packets through socket.
At another layer, Xorg communicates with X11 protocol, which is sent inside TCP packets via its specified TCP socket.
If you do not tell Xorg with IP address to use it defaults to localhost 127.0.0.1. If you leave off the display number it uses display :0 (port 6000). The default local TCP socket used by Xorg on Unix and other Operating Systems is 127.0.0.1:6000
. The commonly recognized host name for 127.0.0.1 is "localhost" (defined in your HOSTS file).
By disabling TCP with the Xorg "-nolisten tcp", it refuses TCP connections to any port, including "the local unix socket".
Of course, the way to know for sure is to just try it. I did, and I posted the results of my tests. It is possible to use other protocols such as UDP, but the version of Xorg installed on the Kindle Touch does lave an option for that listed in its "usage" information, nor do the simple X apps that I tried.
You can read more about it here (and many other places):
If you are aware of *different* "local unix socket" communications method used by Xorg for communicating with local apps, which is not disabled by the Xorg "-nolisten tcp" command line parameter, please enlighten me. Thanks.
EDIT: The reason that I thought this was interesting was that the Kindle Touch is running Xorg natively, and the framework is built on top of Xorg, unlike previous Kindle models which used GTK over DirectFB. There was an X11 hack for the Kindle 2, but I was unable to get that to work on my Kindle 3. In the case of the Kindle Touch, X apps run natively on it using the built-in Xorg (except where disabled by command-line parameters).