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uab 06-06-2004 07:56 PM

how to XDMCP to my school host
Hi, i dont know if this can be done.

But is there any built in app / or x client that allows to me connect to my school computer?

i used to do this using X-win32 under windows.

I basically want to my own local X session running, and have another window with my school X session.

Any help will be appreciated.

TheOther1 06-07-2004 12:32 PM

You need to set up the school machine to do XDMCP.

You could always run VNC on it and connect with the VNC client. Run vncserver :x, where x is a display number like 1. Then run VNCViewer on your Windoze box and connect to machine:x that you chose in the previous step.

You can also connect via SSH, have X-win32 running and start an X app and X-win32 should catch it and display the X session, but X Forwarding needs to be enabled inthe /etc/ssh/sshd_config file.


uab 06-07-2004 01:22 PM

Hey thanks for the reply.

Maybe i wasnt clear.

My school computer already has XDMCP enabled. Its running solaris.

Also, im running Fedora 2, on your post in your response it seems like your telling me to ssh and xwin32?

is there an xwin32 for Linux? that i didnt know.

TheOther1 06-07-2004 05:03 PM

Your post said you used to do it using X-win so I assumed you were still using WinDoze. Sorry.

You should have everything you need to connect in FC2. You can still get redirected X by the SSH method, you don't need X-Win32 since FC2 has an X server already running.

To do XDMCP, log in as any user and issue the command

X -query my.XDMCP.server
where my.XDMCP.server is either the name or IP address of the school XDMCP server.

csfalcon 06-08-2004 12:05 AM

I gave it a try, I am issuing the command from my FC2 machie to FC1 machine.


X -query

Fatal server error:
Server is already active for display 0
If this server is no longer running, remove /tmp/.X0-lock
and start again.
Here does "server" refer to the machine I am connecting too? I need to stop X before issuing this command?

uab 06-08-2004 07:29 AM

Yeah i got the same thing.


alleycat 06-13-2004 07:35 PM

>>>Here does "server" refer to the machine I am connecting too? I need to stop X before issuing this command?<<<

actually, it's referring to the X server on the machine you're issuing the command *FROM*. you can run one mor more X sessions on one or more virtual displays. if your machine is in graphical mode, it's using at least one of them, and by default it's display 0.

X is a little counter-intuitive as far as what it considers a "server" vs "client". (oversimplifying a bit) the machine with the monitor in front of you is a "display server" and doles out screen real estate for "clinet" programs running on the remote machine to use in displaying their output.

try bumping the display number, as in:

X :1 -query

note the ":1" after "X" - you can try higher numbers until one works - depends how many displays your machine has X servers running on, but by default it's usually just :0 on vt7 - do an X --help for more details.

also, you might be interested in the existence of Xnest and gdmXnest which wil run a remote desktop in a window on your own X desktop. just to get you started, here's a command line i use (from within X) to get a desktop on my subnet:

gdmXnest --xnest='Xnest -query -name firewall'

Xnest creates the desktop in a window, and gdmXnest is a nice frontend for it that determines an available display number for you.

on fc2, those are in the xorg-x11-Xnest and gdm packages respectively

hope this helps.

uab 06-13-2004 11:13 PM

Thanks, that works fine ifs local.

What i am trying to do is the same, but instead of having a local session in a window, i want to have a remote session running in a window

something like Xnest -query , which is some ip address.

alleycat 06-14-2004 12:42 AM

it works remotely too, but of course then it depends on their firewall, X authentication, that sort of thing. if it helps - the xdmcp is happening on udp port 177 and the xsessions themselves happen on tcp 6000 and up (i.e. <remote-ip>:0 = 6000, <remote-ip>:11 = 6011 - apologies if you know this already...)

so at that point, it becomes a question of what the firewall will pass and what the xdm/X servers are configured to respond to. just 'cause it works on campus doesn't necessarily mean they'll let it out of their subnet and open it to the big bad internet.

assuming you had a laptop and plugged it in on site and got it to work there, it should work identically from another location by simply using the external address of the server, *IF* they allow that.

if not, you have to talk to them. if it's not open to the world, perhaps they have a vpn that you could get access to? that would effectively get you inside their network, which should then allow a connection, generally.

another alternative - just tried this on my gf's dsl connection (just gave her a spankin' new fc2 box - am i a nice guy, or what? <g>) - you can ssh in if you have that and run something like this:

gdmXnest --xnest='Xnest -geometry 1280+1024 -query -name whatever'

FYI: i tried putting it all on an ssh command line, and it fails. i think it's because when passing a command on the ssh command line, you don't fully log in and the environment isn't set up, but i didn''t pursue the details - yet, anyway. probably some switch i'm leaving out.

it being solaris, it's probably unlikely that they have gdmXnest, in which case you're back to experimenting with display numbers - assuming they have Xnest itself on the remote box, that is. just to test it, i pasted the stuff in the quotes above and added ":15" to the line like so:

Xnest :15 -geometry 1400+1200 -query -name whatever

and it worked the same.

but in both of the above cases, you're actually running the Xnest pgm on the other box and shipping the entire display back to your box, as opposed to running Xnest on your box and connecting to the remote box. more data across the line. to make this work, use "ssh -XC <remote-ip>" - the -X pumps the X connection back to your box (if they allow that - if not, you'll likely get a message right when you log in) and the -C compresses the stream - that actually helps quite a bit in most cases that i've used it.

sorry for the wordy post. i'm still sort of working this stuff out in my head myself.

uab 06-14-2004 02:27 AM

Thanks your being really helpful.

Let me ask you this, if i am use to use X-Win32 using windows and i am able to get the remote login/password screen, it means that school in fact, has it open to the world right?

can you try ? maybe im doing something wrong.

the ip is:

i put Xwin and i was able to connect.

alleycat 06-14-2004 03:19 AM

lol - you're welcome. i know what it's like standing on the side of the road with a flat tire. you hope someone stops.

hmm. well, if you use x-win32 and get a login, there appears to be something else going on.

i tried this:

gdmXnest --xnest='Xnest -query -name test'

and i get the traditional black screen with an "x" cursor. so i scanned udp port 177 and it's closed - hope i don't get a visit from the fbi <g> - i don't normally scan ports on machines i'm not responsible for 'cause network admins can be understandably sensitive about that. anyway, 177 is closed. that's sufficient reason for there to be no login screen appearing.

i don't have x-win32, and i don't use windows much anymore, tho i have access to it either thru a vm or terminal server, so i'm hard put to say what the difference is, but here's my guesses at the possibilities:

- do you already have vpn software running and configured on the windows side? if there's a vpn involved, then you have access to the internal nework. that changes things. it's even possible, tho somewhat unlikely that the hostname maps to an internal ip. try pinging it when logged into windows, then ping it when logged into linux. if the windows one is an addy internal to their network, and the linux one isn't, then you pretty much must have a vpn going on the windows side. if so, you need to reproduce the vpn connection on the linux side. that depends on what software you're/they're using for that, but it'd be likely either some flavor of ipsec or pptp - which can both generally be made to work, tho sometimes they're a bit of a pain.

fwiw, from where i sit,

- perhaps there's some flavor of authentication configured in your x-win32 that punches thru? if so, i don't off the top of my head know what mechanism it's using, but then again, i'm only just finding out enuff about this stuff to be dangerous. assuming you're talking about the x-win32 from starnet, these things from the feature list catch my eye right away:

1) Integrated SSH Connection Module
X-Win32 now includes StarNetSSH, a SSH implementation derived from the open source PuTTY SSH.

2) IPsmarts
Useful when connecting though a NAT router to a host on the Internet.

maybe there's something in the x-win32 connection config that you're not reproducing when trying to connect? i'm thinking like maybe an ssh tunnel or something that it's doing automatically for you.

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