Remote X problem

[Greg Trounson on Melmac]

Greg Trounson wrote:
> I have two Fedora Core boxes here (one FC3 and the other FC4).
> 
> On either of them I can do the following:
> On machine1:
> xhost +machine2;
> 
> On machine2:
> export DISPLAY=machine1:0
> xterm &
> 
> At which point an xterm should appear on machine1, right?
> 
> Wrong.  Well, it always used to, right up until I guess FC2.  But that 
> no longer seems to be the case.  Instead I get:
> 
> xterm Xt error: Can't open display: machine1:0
> 
> What has changed?  How can I get remote X programs to work?
> 

To answer my own question:

Fedora makes use of GDM, and since FC2 an option called "DisallowTCP" 
has been set by default, which tells the X server not to listen on TCP 
port 6000.  Why on earth anyone would want to block remote X11 this way 
is quite beyond me, when any decent firewall can do it without requiring 
a restart of gdm.

To fix it, open the file /etc/X11/gdm/gdm.conf, and change this:

#DisallowTCP=true

to this:
DisallowTCP=false

Remember to remove the '#' at the start.

Unfortunately you will need to restart gdm for the changes to take 
effect.  A "telinit 3; telinit 5" will usually fix this.

It's also good to check that your firewall allows access to port 
6000-6010 for machines you want to be able to connect.

Greg