---- # 5.6 The X Display Manager ***Contributed by Seth Kingsley.*** ## 5.6.1 Overview The X Display Manager ( **XDM** ) is an optional part of the X Window System that is used for login session management. This is useful for several types of situations, including minimal "X Terminals", desktops, and large network display servers. Since the X Window System is network and protocol independent, there are a wide variety of possible configurations for running X clients and servers on different machines connected by a network. **XDM** provides a graphical interface for choosing which display server to connect to, and entering authorization information such as a login and password combination. Think of **XDM** as providing the same functionality to the user as the [getty(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=getty§ion=8) utility (see [ Section 17.3.2](term.html#TERM-CONFIG) for details). That is, it performs system logins to the display being connected to and then runs a session manager on behalf of the user (usually an X window manager). **XDM** then waits for this program to exit, signaling that the user is done and should be logged out of the display. At this point, **XDM** can display the login and display chooser screens for the next user to login. ## 5.6.2 Using XDM The **XDM** daemon program is located in `/usr/pkg/xorg/bin/xdm`. This program can be run at any time as `root` and it will start managing the X display on the local machine. If **XDM** is to be run every time the machine boots up, a convenient way to do this is by adding an entry to `/etc/ttys`. For more information about the format and usage of this file, see [ Section 17.3.2.1](term.html#TERM-ETCTTYS). There is a line in the default `/etc/ttys` file for running the **XDM** daemon on a virtual terminal: ttyv8 "/usr/pkg/xorg/bin/xdm -nodaemon" xterm off secure By default this entry is disabled; in order to enable it change field 5 from `off` to `on` and restart [init(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=init§ion=8) using the directions in [ Section 17.3.2.2](term.html#TERM-HUP). The first field, the name of the terminal this program will manage, is `ttyv8`. This means that **XDM** will start running on the 9th virtual terminal. ## 5.6.3 Configuring XDM The **XDM** configuration directory is located in `/var/lib/xdm`. The sample configuration files are in `/usr/pkg/share/examples/xorg/xdm/`, in this directory there are several files used to change the behavior and appearance of **XDM** . Typically these files will be found: || **File** || **Description** || || `Xaccess` || Client authorization ruleset. || || `Xresources` || Default X resource values. || || `Xservers` || List of remote and local displays to manage. || || `Xsession` || Default session script for logins. || || `Xsetup_`* || Script to launch applications before the login interface. || || `xdm-config` || Global configuration for all displays running on this machine. || || `xdm-errors` || Errors generated by the server program. || || `xdm-pid` || The process ID of the currently running XDM. || Also in this directory are a few scripts and programs used to set up the desktop when **XDM** is running. The purpose of each of these files will be briefly described. The exact syntax and usage of all of these files is described in [xdm(1)](http://leaf.dragonflybsd.org/cgi/web-man?command=xdm§ion=1). The default configuration is a simple rectangular login window with the hostname of the machine displayed at the top in a large font and "Login:" and "Password:" prompts below. This is a good starting point for changing the look and feel of **XDM** screens. ### 5.6.3.1 Xaccess The protocol for connecting to **XDM** controlled displays is called the X Display Manager Connection Protocol (XDMCP). This file is a ruleset for controlling XDMCP connections from remote machines. It is ignored unless the `xdm-config` is changed to listen for remote connections. By default, it does not allow any clients to connect. ### 5.6.3.2 Xresources This is an application-defaults file for the display chooser and the login screens. This is where the appearance of the login program can be modified. The format is identical to the app-defaults file described in the X11 documentation. ### 5.6.3.3 Xservers This is a list of the remote displays the chooser should provide as choices. ### 5.6.3.4 Xsession This is the default session script for **XDM** to run after a user has logged in. Normally each user will have a customized session script in `~/.xsession` that overrides this script. ### 5.6.3.5 Xsetup_* These will be run automatically before displaying the chooser or login interfaces. There is a script for each display being used, named `Xsetup_` followed by the local display number (for instance `Xsetup_0`). Typically these scripts will run one or two programs in the background such as `xconsole`. ### 5.6.3.6 xdm-config This contains settings in the form of app-defaults that are applicable to every display that this installation manages. ### 5.6.3.7 xdm-errors This contains the output of the X servers that **XDM** is trying to run. If a display that **XDM** is trying to start hangs for some reason, this is a good place to look for error messages. These messages are also written to the user's `~/.xsession-errors` file on a per-session basis. ## 5.6.4 Running a Network Display Server In order for other clients to connect to the display server, edit the access control rules, and enable the connection listener. By default these are set to conservative values. To make **XDM** listen for connections, first comment out a line in the `xdm-config` file: ! SECURITY: do not listen for XDMCP or Chooser requests ! Comment out this line if you want to manage X terminals with xdm DisplayManager.requestPort: 0 and then restart **XDM** . Remember that comments in app-defaults files begin with a "!" character, not the usual "#". More strict access controls may be desired. Look at the example entries in `Xaccess`, and refer to the [xdm(1)](http://leaf.dragonflybsd.org/cgi/web-man?command=xdm§ion=1) manual page for further information. ## 5.6.5 Replacements for XDM Several replacements for the default **XDM** program exist. One of them, **kdm** (bundled with **KDE** ) is described later in this chapter. The **kdm** display manager offers many visual improvements and cosmetic frills, as well as the functionality to allow users to choose their window manager of choice at login time. ----