[lug] remote clients can't display on FC3/KRUD

rm at fabula.de rm at fabula.de
Sun Jun 19 13:32:21 MDT 2005

On Sun, Jun 19, 2005 at 11:34:31AM -0600, D. Stimits wrote:
> rm at fabula.de wrote:
> >On Sat, Jun 18, 2005 at 11:45:00PM -0600, Michael J. Hammel wrote:
> >
> >>On Sat, 2005-06-18 at 18:19 -0600, D. Stimits wrote:
> >>
> >>>By default the X11 servers accept only UDP connections...remote machines 
> >>>use TCP. You have to turn on the TCP option in
> >>>/etc/X11/gdm/gdm.conf
> >>>There is a line there, DisallowTCP=true. Kind of misleading, as not 
> >>>having this parameter still disallows TCP. Change it to 
> >>>DisallowTCP=false.
> >>
> >>That's the ticket.  Thanks D. I can now run GIMP on the server and
> >>display it on the laptop to continue working on my next book.
> >>Woohoo!  :-)
> >
> >
> >Just a small correction: once tcp/ip connections are disabled (as they are
> >indeed on most security aware distros) the X server only listens on a local
> >(Unix) socket (normally under /tmp/.X11-unix/....). AFAIK it's _not_ 
> >possible
> >to use udp/ip for X connections.
> I never said udp/ip :P, just udp. 

Yes, that was intentional :) My point: udp _is_ an IP protocol (unless you 
show me how to create a create an udp socket that's _not_ of type PF_INET ...).

> Processes using a unix socket in one 
> way or another are udp enabled, regardless of how the socket/file is 
> exposed.

Hmm. Might it be possible that you mix up 'udp' (as of RFC768 - part of
the inet family) with 'datagram' (a socket _type_). 

> X11 by nature is networked...it isn't possible to run X11 
> without networking functionality, although protocols and socket details 
> are flexible.

Again - depends on what you consider 'networking'. You can run X11 without any
inet capabilities in the kernel as long as PF_UNIX is supported. I'd consider 
Unix sockets to be part of the interproces comunication. 

On the topic of X11 over udp: somehow that seems "wrong": after all, you really don't
want to have part of your X11 event stream just disapear (not nice when some of the
password characters you typed in don't make it to the X client :-/
Also, we want those 'connection to X server borken ...' (which isn't possible with udp).
In theory it _would_ be possible to use _datagrams_ over Unix domain sockets on Linux
since, according to the docs, "... as on most Unix implementations, Unix domain datagram sock-
ets are always reliable and don't reorder datagrams". But i just checked my local box:

  hobbes:~$ ps aux | grep '[X] :0'
     root      3439  2.9 13.0  84504 41764 ? S< 13:24 15:23 /usr/X11R6/bin/X :0 -br -audit 0 -auth ...

  ralf at hobbes:~$ lsof -p 3439
  ralf at hobbes:~$ sudo lsof -p 3439 | grep /tmp/
  Xorg    3439 root    4u  unix 0xd220ce20               5709 /tmp/.X11-unix/X0
  Xorg    3439 root   10u  unix 0xd3459c40               6412 /tmp/.X11-unix/X0
  Xorg    3439 root   18u  unix 0xc8713200              20649 /tmp/.X11-unix/X0
  Xorg    3439 root   23u  unix 0xc793ecc0              21037 /tmp/.X11-unix/X0
  ralf at hobbes:~$ sudo netstat -p 3439  | grep tmp/.X11-unix/
  unix  3      [ ]         STREAM     CONNECTED     21037    3439/X              /tmp/.X11-unix/X0
  unix  3      [ ]         STREAM     CONNECTED     20649    3439/X              /tmp/.X11-unix/X0
  unix  3      [ ]         STREAM     CONNECTED     16425    3439/X              /tmp/.X11-unix/X0
  unix  3      [ ]         STREAM     CONNECTED     9654     3439/X              /tmp/.X11-unix/X0
  unix  3      [ ]         STREAM     CONNECTED     8579     3439/X              /tmp/.X11-unix/X0
  unix  3      [ ]         STREAM     CONNECTED     8550     3439/X              /tmp/.X11-unix/X0
  unix  3      [ ]         STREAM     CONNECTED     8547     3439/X              /tmp/.X11-unix/X0
  unix  3      [ ]         STREAM     CONNECTED     6412     3439/X              /tmp/.X11-unix/X0
  ralf at hobbes:~$

seems like the Xserver uses socket type stream.

 Cheers Ralf Mattes

o D. Stimits, stimits AT comcast DOT net
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