[NCLUG] X, xhost, xauth, stuff like that...

[Gary Rogers]

Try:
    xhost+
    ssh A

    DISPLAY=B:0; export DISPLAY
    xterm

    That should prove if the display is exporting properly. I suspect Gnome
foulplay.
    

on 9/13/01 10:00 PM, S. Luke Jones at luke at frii.com wrote:

> I've been reading the X* howtos and frankly I'm still confused.  Can some
> one (or all of you) who actually understand this stuff check me on this?
> 
> I'm sitting in front of a machine, call it A.  If I understand the
> terminology, I'm running an X server and some number of X clients (xterm,
> Netscape, ...) on machine A.  If I look at my $DISPLAY variable it's
> ':0.0' meaning the local host display 0 screen 0. So far, so good.
> 
> Now, I have another machine B that has a crappy monitor and is in an
> inconvenient place but nonetheless has a lot to recommend it, e.g., it
> has a dialout connection -- and, yes, I could use IP masquerading but
> let's ignore that because I'm talking about X here. Okay, scratch the
> dialout. Say it has a faster CPU (in fact, two CPU's, both of them faster)
> and twice as much RAM.  I'd like to, uh, encode some MP3's and, um, I want
> to use a spiffy graphical MP3 encoding application ("X client", yes?) from
> this machine A with the nice monitor on that machine B with the big iron.
> 
> So I open an xterm here on A and ssh over to B.
> 
> luke at A $ ssh B
> luke at B $ gmp3enc foo.wav
> Gtk-WARNING **: cannot open display:
> 
> OK. Now I need to tell the MP3 encoding client that my actual X server is
> over here.
> 
> luke at B $ export DISPLAY=':0.0'
> Gtk-WARNING **: cannot open display: :0.0
> 
> Oops. That's not here, that's there.
> 
> luke at B $ export DISPLAY='A:0.0'
> Gtk-WARNING **: cannot open display: A:0.0
> 
> Sigh. Assuming that 'A' is resolving correctly -- and at least for "ping"
> it is, not because I understand DNS but because it really isn't that big
> a hassle to maintain two 2-line /etc/hosts files :-) -- then is it fair
> to say that the reason for this most recent error is because the X server
> here on A is rejecting the overtures of B?
> 
> Assuming this is true, then I gather what I really don't want to do is
> via "xhost +B" over here on A, because that's a really lame 80's kind of
> insecure solution. Which is fine with me because it doesn't work anyway,
> at least when I did it:
> 
> luke at A $ xhost +B
> B being added to access control list
> luke at A $ ssh B
> luke at B $ gmp3enc foo.wav
> Gtk-WARNING **: cannot open display: A:0.0
> 
> So that leaves me with xauth, and maybe it's just because it's late and
> I'm tired, but I can't make heads or tails of that. The man page, is
> IMHO, impenetrable. I don't even use XDM (or GDM or KDM or whatever). I
> just do an old fashioned startx from, yes -- I'm not afraid to say it
> -- the command line. On the other hand, the kind folks at Red Hat have
> apparently done something with it because I have a .xauth directory
> hierarchy in my $HOME.
> 
> Sigh and double-sigh. Bother. Can anyone recommend a HOWTO or other
> material that spells this out in one-syllable words for an old duffer
> like me?