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Linux: Display a login banner for Gnome (GDM) Desktop

You can easily use /etc/issue file to display a pre-login message / login warning banner for text based session. You can also force OpenSSH (SSHD) to display a login message or banner. But how do you force GDM to display a login banner for all local and remote users?

GDM customization

GDM is a replacement for XDM, the X Display Manager. GDM runs and manages the X servers for both local and remote logins (using XDMCP). You can easily configure GDM to display message. You need to open gdm custom configuration file:

[a] RHEL / CentOS / Fedora Linux : Open /etc/gdm/custom.conf file.
[b] Debian / Ubuntu Linux : Open /etc/gdm/gdm.conf-custom file.

This file is the appropriate place for specifying your customizations to the GDM configuration. If you run gdmsetup, it will automatically edit this file for you and will cause the daemon and any running GDM GUI programs to automatically update with the new configuration. Not all configuration options are supported by gdmsetup, so to modify some values it may be necessary to modify this file directly by hand.

Display a login banner for Gnome / GDM under Linux

Open /etc/gdm/custom.conf file:
# vi /etc/gdm/custom.conf
Find out [greeter] section and append following text:
Welcome=Message for local users
RemoteWelcome=Message for remote login users

Save and close the file.

A note about RHEL / CentOS / Fedora user

Apart from above configuration you also need to add following line inder the [daemon] section:

Using GUI tool gdmsetup

gdmsetup is a graphical tool for easily changing the most commonly used options including greeting messages. As I mentioned earlier gdmsetup does not support changing of all onfiguration variables, so it may be necessary to edit the files by hand for some configurations and security issues. Open X terminal and enter the command:
$ sudo gdmsetup
How do I display a login warning banner for GDM under Linux / UNIX with gdmsetup?
(click to enlarge)

Select Local tab > Welcome Messages > Custom > Enter your custom message > Click on Close button to save the changes.

Sometime you may see different language encoding in X than on your console (tty) prompt. Sometime two different user need two have different language encodings.

~/.dmrc file - Per-user language support

In theory this file should be shared between GDM (Gnome) and KDM (KDE), so users only have to configure things once. This is a standard .ini kind / style configuration file. It has only one section called [Desktop] which has two keys: Session and Language. There are some per user configuration settings that control how GDM behaves. GDM is picky about the file ownership and permissions of the user files it will access, and will ignore files if they are not owned by the user or files that have group/world write permission. Normally GDM will write this file when the user logs in for the first time, and rewrite it if the user chooses to change their default values on a subsequent login.

Setup language encoding in X

Defining LANG variable is not sufficient, you need to setup language encoding using ~/.dmrc file.
cat ~/.dmrc


Refer to Gnome Display Manager Reference Manual for more information.