You should now be able to query the server. These instructions are not officially documented and therefore this functionality may be considered a work in progress. This author believes that this functionality is indeed a work in progress because he has observed the following bugs: An inability to login by default with Xming clients at least. An inability of Xnest clients to reconnect. The server reports that the maximum number of sessions from a host have been reached, even though the session has been entirely ended.

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Next 2. The pre-requisite is to have a any Linux distribution installed and running X. Before you begin, some background Before you begin, it is better to have a basic understanding of how this works. In this X DM Wiki page, it gives you a basic understanding of how it works!

This document will use gdm and kdm as an example. The Display Manager provides a nice and consistent interfaces for general users X-based login, starting up a window manager, clock, etc.

X Display Manager manages a collection of X displays, which may be on the local host or remote servers. It is worth noting that the Xsession file is what runs your environment. When xdm runs, it offers display management in two different ways. The gdm Gnome Display Manager is a re-implementation of the well known xdm.

The gdm. The new interface is aimed for XP feel and styles. The setup makes no difference in this case! All OSs are vulnerable to the hackers, if the user does poor configuration job or maintaining the security updates!

If you must use XDMCP, be sure to use it only in a trusted networks, such as corporate network within a firewall. Never use it in the open network or Internet environment without a firewall protection! If you are using at home, remember to add a firewall equipped router for protection. A good way to test your network security is to test it using the ShieldsUp by Gibson Research. It is free and easy to use! Check this Why Port Forwarding? If you would like to experiment this, I have add a little section below to show you how it works.

RH Workstation v. Fedora Core v. The new RH free version Mandrake Linux from 7. I would also like to test it out on the new Mandriva Spring version. Ubuntu version 6. SuSE 7. I would like to thank all users who help me on this project.

The other I have tried on is Caldera eDesktop 2. I have not had a chance to test it on other Linux flavors like Debian, Turbolinux, Gentoo, etc. However, the setup should be similar and should work just fine. If you have successfully setup one other than the distribution listed above, please share it with me.

I will add them into this document. There are also many open-source applications, as well as commercial one available, if you happen to have one. Server Preparation In RH 7. You would need the root privileges to update the naming information. In my case, I use mostly Fedora Core 6 in my lab and Ubuntu 7. Also, most dists now come with firewall installed by default unless you choose not to.

You may encounter problem, if you do not add firewall rules or temporary disable it in setting up XDMCP. I will not cover the firewall rules here in details, since this is not the focus of this document. I will share with you only on how to make it works first and you can fine-tune it yourself.

To show your firewall rules, in kernel 2. For kernel 2. You should be able to use the iptables in the similar way. Check for iptables references at the Resources area or this setup example. One other easy way is to add rules that only accept certain IP address es from your trusted workstations.

Please feel free to experiment it by using the iptables command. Again, I will not cover the details here. If you would like to use the GUI tool to configure the firewall using iptables, try this good one: the Firestarter. Setup your Networking. To test it out, you can use the ping, ftp and telnet command to determine if your are networking. Remember to enable it, if you prefer to use it for your test. You can always turn it off when you are done Using ntsysv in RH, or rcconf, sysvconfig in Ubuntu and Debian, with root privilege.

One other thing is to remember firewall rules are there. Add your own rules or temporary disable it as mentioned above to make these commands work. Setup X. Do not setup with a resolution higher than what the remote users are able to use for their display.

The newer version is now capable of probing the video chipset and determine that for you. Some older X version may not! Test the X Server by typing either startx or telinit 5. Make sure X is running properly.

Creates the necessary user account s and associated group for user who will access via the Xterminal. Steps to Complete the Procedures Although X can use the local fonts, it is better to use the xfs font server in an networking environment. If this is what you want in Linux X environment, you need to provide font using either X font server xfs or hard coded font path in XF86Config and XF86Config-4 configuration files.

If you plan to use xfs font server check here to see the xfs advantages. If you plan to use local fonts, you can skip step 1. Change all lines this is where the Font Server port , if the port is not set to You can set a different port, as long as you carefully plan it first to make sure no conflicts in using the port number and change it accordingly. This is for security reason.

Find this line: DisplayManager. For gdm setup, it is in the following section. An example can be found in the Resources. From "System" menu, go to "Administration" and the "Login Window" Alternatively, you can use "sudo gdmsetup" command. Click the "Remote" tab and in "Style", select "Same as Local". Additional setup is in the "Security" tab and the lower "Configure X Server You must restart gdm to enable it!

Doing this is quick and simple, but you lose the sense of what files are being touched and changed! Easy of use or controllability is your choice here! The digit here meaning the default runlevel. For X, the runlevel should be "5". Before changing this line, you can use the telinit command to test prior to modifying the line. Use either telinit 3 to set to level 3, or telinit 5 to set to level 5, graphics mode you can issue this command on the second machine that telnets into this server.

Runlevel is the same in Debian and Ubuntu. Since Ubuntu 6. Each event is trigger or changed by issuing the telinit 3 command. Edit the xorg. To save your time and energy, I recommend you to add the FontPath in the xorg. If you are not sure what fonts are available to you, you can use this command to check it out requires root : chkfontpath --list The following are some of the example fonts for your reference. Make sure you have these fonts before editing these path. You can keep the default setting, but this is what I prefer.

If you are not sure, leave this alone. This is not a required step, but of a personal preference! There is no need to do this in Ubuntu and newer Debian dist.

You are now ready to run a test. Adding this script or not is your preference. It is not required step here! I find it easier using the X Server and another machine to test it: Re- Start your X which is in runlevel 5 or runlevel 2 in Ubuntu. If you are not sure how to do this, simply reboot your system but this is really not necessary, if you know how to restart it using command line. If you have not modify your firewall rules, you need to temporary disable it by using iptables -F or ipchains -F.


CentOS / RHEL 6,7 : How to enable or disable XDMCP service (GDM)

Copyright Information 1. I am always looking for the best way to use Linux, both at home and in work. This is how I came up with this document as a way to share my experiences with all users. Disclaimer No liability for the contents of this documents can be accepted. Use the concepts, examples and other content at your own risk.



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