XLaunch - XDMCP settings

XDMCP settings

Settings for the

XDMCP mode. This mode is the most problematic, is not secure, and usually requires altering of the remote machine's settings. Remote Display Managers listen for the XDMCP protocol on port 177/UDP. But the actual X11 protocol connections will be made to the local port 6000+n /TCP, where n is the display-number.

You can test for responding XDMCP hosts on your network using XPing interactively or just simply by using the -find command line option.

Connect to host

Enables XDMCP and sends Query UDP packets to the specified host.

XDMCP host chooser

Enter the hostname of the machine you want to connect. You can also select a hostname from a chooser list of up to ten hosts. This list can be customised by adding (hand editing) tags Host1="a" to Host10="j" to a config.xlaunch file (i.e. a previously saved XLaunch configuration file). XDMCPHost="x" is the machine that is actually connected.

XPing. Hosts are dynamically found that reply Willing to sent Queries by using .xlaunch configuration file entries XDMCPHost, Host1-Host10, and any entered host, as the list to XPing. The replies are accumulated, and the chooser re-populated. Each line shows the host plus any output from the remote Xwilling file. (Hosts can be entered in IP address dotted format and characters after host'whitespace' are not used by later processing)
If host entry BROADCAST is used then BroadcastQuery is sent and all Willing hosts collected from the network. BROADCAST is sent automatically, if the host entry is empty, so that XPing always does something obvious.

Reset. The chooser can be reset to Host1 to Host10 plus any selected host or, if none, XDMCPHost as the chosen host.

The XPing and Reset buttons are not available together. Use the pair of buttons in rotation.

Use indirect connect

Enables XDMCP and sends IndirectQuery packets to the specified host. This host presents a chooser box of several hosts or sends ForwardQuery to another host depending on how its X Display Manager is configured (via Xaccess file entries).

Search for hosts (broadcast)

Enables XDMCP and broadcasts BroadcastQuery packets to the network. The first responding display manager will be automatically chosen for the session (i.e. no choice of host compared with using XPing or -find).

XDMCP remote settings

A quick guide to setting insecure XDMCP mode on a remote machine running kdm, gdm, xdm or wdm...

On the remote Linux/Unix machine edit the following files and then restart the appropriate X Display Manager (which must not be run with the -nolisten tcp option, or similar...this maybe the default setting in your distro!)

Edit the file Xaccess (each Display Manager has its own). Make sure you have a line like this that is uncommented.
```
*     	#any host can get a login window
```
Edit the X Display Manager config file (kdmrc, gdm.conf, xdm-config or wdm-config). Some distros have these files in multiple locations: find and change the 'working' one.
```
[Xdmcp]
Enable=false (may be shown as 0 in some distributions)
  to
[Xdmcp]
Enable=true (or 1 in some distributions)
```
or for a xdm style configuration
```
DisplayManager.requestPort:	0
  to
!DisplayManager.requestPort:	0
```

If you have problems: use Wireshark or equivalent to monitor UDP traffic on the remote host and look for a protocol sequence, e.g. Query 177/UDP, Willing x/UDP, Request 177/UDP, Accept x/UDP, Manage 177/UDP, and see where it stops. If it gets through a sequence: test with local and remote xeyes in multiwindow mode, because the Display Manager acts just like an X client from then on in to provide its login window.

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