Thursday, July 24, 2014

Customizing the UNIX User Environment - Part 3 - UNIX X window managers and desktops - Part 1

Customizing the UNIX User Environment


UNIX X window managers and desktops




The X Display Manager (XDM) is a program that manages login sessions for the X Window System.


XDM prompts users for theor username and password. Then it authorizes them and opens a session on an X server for them.

When a user exits the X interface. XDM closes the session and prompts the next user for their username and password.


XDM is particularly useful in large network implementations that have more than one X dispay server. In such cases, XDM allows users to choose which server they want to connect to.


To start XDM, you run the XDM binary, which in this case is located in the /usr/X11R6/bin directory. You need to be logged in as root to do this.


You can configure a system so that XDM runs automatically when the system starts up. The procedure for doing this varies from one flavor of UNIX to another.


If you're using a system with virtual terminals - such as FreeBSD - you can add a line to the /etc/ttys file that automatically runs XDM in one of the virtual terminals. In this example, XDM uses the ninth virtual terminal.


Once you've started XDM, it display a graphical login window whenever a user needs to login.

You can customize the appearance of this window. This example shows a common default.


You can configure XDM by editiong the following files, all of which are located in /usr/X11R6/lib/X11/xdm:

- xdm-config - file contains flobal default settings that apply to all of the displays to which users can connect

- xdm-errors - file contains a record of error messages generated by the X sessions that XDM runs. It's useful for troubleshooting

- xdm-pid - file allows you to specify the process ID of the XDM process.

- Xaccess - file contains a set of rules for controlling access to XDM. You can use it to determine how remote X client connections are authorized.

- Xresources - file contains default settings for the appearance of the login screen, and specifies the default display server.

- Xservers - file lists all the remote display servers to which users of XDM can connect. They can choose any of these servers when they log in.

- Xsession - file is the default session script that runs when users log in and start a session.


Note : The directory in which these files are located may differ depending on the UNIX implementation you're using.


In addition to the XDM configuration files, the /usr/X11R6/lib/X11/xdm directory contains a set of display setup scripts.

These scripts are named Xsetup_0, Xsetup_1, and soon. You can use them to specify background processes that run automatically when XDM starts an X session on a particular display.

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