Ict-innovation/LPI/106.2

= 106.2 Set Up a Display Manager = ''Candidates should be able set up and customize a display manager. This objective covers the display managers XDM (X Display Manger), GDM (Gnome Display Manager) and KDM (KDE Display Manager).''

Key Knowledge Areas


 * Turn the display manager on or off.


 * Change the display manager greeting.


 * Change default color depth for the display manager.


 * Configure display managers for use by X-stations.

The Display Manager
There are three main display managers, xdm (generic), gdm (GNOME) and kdm (KDE). A display manager will automatically be started if the system is running in a given runlevel (e.g runlevel 5). We first describe the login process; the next section covers more advanced functionalities of a Display Manager. The login process follows the following steps:

xdm --> xlogin --> Xsession --> (optionally) Xclients or ~/.Xclients

Different versions of display managers as well as different Linux distributions may use slightly different steps. In general however, note that startx uses xinit whereas xdm uses Xsession.

Customising

Each user can further customise their environment by using a .xinitrc file. This file will be merged into the system xinitrc. The switdesk tool allows users to define a custom .Xclients file

KDM

This display manager is installed with the KDE desktop environment. It is based on the generic xdm display manager and shares many common configuration files. These configuration files for are in /usr/share/config/kdm. The file that controls most functionalities is kdmrc.

The path to the kdm binary is '''/usr/bin/kdm. '''And the KDM Configuration files:

kdmrc Xaccess (same as xdm) Xservers (same as xdm) Xsession (same as xdm) Xsetup Xstartup 

GDM

This display manager is distributed with the GNOME desktop environment. The main configuration file is gdm.conf

The path to the gdm binary is '''/usr/bin/gdm. GDM Configuration Files ( <tt>/etc/X11/gdm</tt>):'''

Sessions/ gdm.conf 

XDM

The xdm display manager is part of the Xfree86 application. The main configuration file is xdm-config

The path to the xdm binary is <tt>'''/usr/bin/xdm. '''</tt>XDM Configuration Files:

Xaccess    Xresources  Xsession  xdm-config  Xservers

We will look at the xdm configuration files in more detail later in this section.

Display Managers are used mainly in run level 5:

Display managers allow local users to log onto the system using the graphical interface. They can also be used to provide a graphical login interface over the network. For this they use a protocol called XDMCP or X Display Manager Control Protocol. By default XDMCP is disabled (we will enable XDMCP as an exercise).



Configuration Files

<tt>/etc/X11/xdm/Xrescources</tt>

Since the Display Manager is also an x-application, the fonts, the background colors and <tt>xlogin </tt>can be configured with the <tt>Xresourses</tt> file in <tt>/etc/X11/xdm/</tt>. When using <tt>gdm</tt>, the <tt>/etc/X11/gdm/Init/Default</tt> script will source <tt>Xresources</tt>.

<tt>/etc/X11/xdm/Xservers</tt>

This file simply maps the name of a display with an X server. For example display: 0 is understood to be the local X server. Remember that X always runs on the first free <tt>/dev/tty</tt>.

<tt>/etc/X11/xdm/xdm-config</tt>

This is the main configuration file for xdm. It is also used to enable XDMCP (see exercises)

<tt>/etc/X11/xdm/Xaccess</tt>

This file is used to enable XDMCP, allowing remote hosts to directly connect to the local server (using -query) or query about other display

Since the Display Manager is also an x-application the Xresources file is similar to the .Xresources file except that it controls how the login screen is displayed.



The following is a partial list of the files, terms and utilities that were used.


 * startx
 * xinit
 * gdm
 * xdm
 * kdm
 * /etc/X11/xdm/Xresources
 * xdm-config 

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