Assuming that you want all display on the linux screen, switchable
between the 2 X servers;

The second X server on the linux host needs to broadcast or query for
XDMCP.

        X :1 -broadcast tty#    (# = tty to attach X)
   or
        X :1 -query macppc tty## (# = tty to attach X)

   or if you want to be able to pick the xdm host dynamically

        X :1 -indirect macppc tty#  (# = tty to attach X)

The macppc needs an xdm to be configured to accept
query/broadcast/indirect (Xaccess)/

You do not need the xhost, as authorization is managed in the X/xdm
connection, and you do not need the foreign entry. You only need an
xdm on the linux host if you want to replace the startx for the first X.

fission writes:
 > Hello,
 > 
 > I have two computers set up:
 > 
 > 1) Linux on a Pentium/75
 > 2) NetBSD/macppc 1.4.1 on a Performa 6400
 > 
 > The Performa 6400 right now is running off of a serial console, and so,
 > isn't at all good for running an X server on.  However, the Linux computer
 > is configured well for X servers.  What I want to do is run two X servers
 > on my Linux computer: one normal one whenever I type 'startx' that goes to
 > :0 and another one that runs via xdm on my NetBSD/macppc computer.
 > What I did was:
 > 
 > 1) Set up /usr/X11R6/lib/X11/xdm/Xservers to remove the local client and
 > add the foreign client:
 > 	nucleus:1 foreign
 > 
 > 2) Start X on the linux computer:
 > 	X :1
 > 
 > 3) Let the NetBSD/macppc computer run an xdm on it:
 > 	xhost +positron
 > 
 > 4) Start up xdm on the NetBSD/macppc computer.
 > 	xdm
 > 
 > What happened:
 > 
 > On the Linux box, I got a whole bunch of messages like:
 > 
 > 	AUDIT: Sun Mar 12 21:03:08 2000: 18475 X: client 1 rejected from IP
 > 	192.168.0.10 port 65494
 > 
 > And on the NetBSD computer, I get many
 > 	_X11TransSocketINETConnect: Can't connect: errno = 61
 > 
 > As well as the occasional:
 > 	xdm error (pid 334): server open failed for nucleus:1, giving up
 > 	xdm error (pid 329): Display nucleus:1 cannot be opened
 > 	Xlib: connection to "nucleus:1.0" refused by server
 > 	Xlib: Client is not authorized to connect to server
 > 
 > 
 > How is this properly set up?  Should I be running xdm on both my Linux
 > host and my NetBSD/macppc and linking the two?  Help, please!
 > 
 > Thanks in advance,
 > 
 > --
 > Tyler Mitchell

-- 
Rex McMaster                       rex@mcmaster.wattle.id.au
                     http://www.compsoft.com.au/~rmcm/pgp-pk