The greeter is the graphical user interface that is presented to the user. The greeter contains a menu at the top, an optional face browser, an optional logo and a text entry widget.
The text entry field is used for entering logins, passwords, passphrases etc. gdmlogin is controlled by the underlying daemon and is basically stateless. The daemon controls the greeter through a simple protocol where it can ask the greeter for a text string with echo turned on or off. Similarly, the daemon can change the label above the text entry widget to correspond to the value the authentication system wants the user to enter.
The menu bar in the top of the greeter enables the user to select the requested session type/desktop environment, select an appropriate locale/language and optionally shutdown/reboot the machine. The greeter window can also be iconified to make room for other applications on the login screen.
The greeter provides a face browser containing icons for all the users on a system. The icons can be installed globally by the sysadmin or in the users' home directories.
The face browser makes a few assumptions about your environment. First of all, the greeter runs under a dedicated userid, and therefore any face icons located in user directories must be readable to the gdm user. I.e. all home- and ~/.gnome directories must be made readable and executable to the ``other'' group on the system.
Similarly, face icons placed in the global face directory must be readable to the gdm user.
Please note that loading and scaling face icons located in user home directories can be a very time consuming task. Especially on large systems or systems running NIS. The browser feature is only intended for systems with relatively few users.
To filter out unwanted user names in the browser, an exclude option is implemented. The greeter will automatically ignore usernames listed in the Exclude statement in the config file.
When the browser is turned on, valid usernames on the machine are inherently exposed to a potential intruder. If your system is connected directly to the Internet, this might be a bad idea.
The greeter can optionally display a logo in the login window. The image must be in a format readable to the Imlib library (GIF, JPG, PNG, TIFF, XPM and possibly others), and it must be readable to the gdm user. See the Logo option in the reference section below for detauls.