xlogin-xdmcpserver(8)         xlogin-xdmcpserver         xlogin-xdmcpserver(8)



NAME
       xlogin-xdmcpserver - Listen for xdmcp UDP data and answer, spawns xlogin processes to satisfy
       requests

SYNOPSIS
       xlogin-xdmcpserver <ARGUMENTS>

DESCRIPTION
       xlogin-xdmcpserver is a server program for the X windows X Display Manager Control  Protocol.



OPTIONS
       All options specified here become the command line arguments for xlogin when spawned.

       The server process itself has no arguments other than -help

       At the moment the server only supports X servers asking for a session with the -query option,
       chooser modes are not currently implemented.

       To get a session from a remote machine try something like:

       X -query <servername> :Local display number

       A real world example would be :

       X -query 192.168.1.116 :1

       Note the space between the IP and the display number, it matters !

       The xlogin-xdmcpserver should send the requesting X server a cookie  then  launch  an  xlogin
       process to satisfy the query.


SECURITY
       Poor  ! Lets be honest here XDMCP is a pretty weak protocol from a security perspective.  Its
       biggest downfall is that the cookie, a kind of "poor mans secret key"  is  handed  to  the  X
       server  generating  the query via the X socket.  This can be sniffed by another network user,
       the time window is pretty small but its possible.

       If security is very high on your list then you should not be running  distributed  X  windows
       without extra encryption.

       Even with the secuirty issues for some home, small office and school users its still a useful
       way of doing things. A secret is still a secret as long as  nobody  was  listening  when  you
       shouted it across the room.

EXAMPLES
       xlogin-xdmcpserver -date -pos 10,10 -background tree


BUGS
       Its conventional to be able to chose the listening socket.

       Its possible to specify -identity on the command line for automatic logins for any requesting
       X server. This is a bad idea as almost everything stores some transient state  in  the  users
       home  directory.   Even  firefox without a window manager is not safe in this mode.  Don't do
       it, its not big or clever and having multiple sessions with the same home directory will piss
       off KDE/GNOME something rotten.

       Currently  this  implementation  does not hold much in the way of state, it simply replies to
       all queries with a positive response. Its like an old relative at  a  family  gathering  that
       replies  with "yes dear" to all questions but doesn't in fact listen the conversation at all.

       On paper a race condition exists where an X server sending a second query could bump into the
       xlogin-xdmcpserver just after its started to spawn an xlogin process. The result would be two
       xlogin processes, with access controls on the second cookie exchange would  fail,  but  users
       running  with  -ac  as well could get two login boxes. I've never seen this in the real world
       but it is possible.

AUTHOR
       Jonathan Andrews

SEE ALSO
       xlogin(8)  xlogin-makeidentity(8)  xlogin-rootjpeg(8)




version 0.2                   September 14, 2008         xlogin-xdmcpserver(8)