Setup a Display Manager for Xfce
LightDM is the default display manager for Edubuntu, Xubuntu and Mythbuntu since 11.10 release, for Lubuntu since 12.04 release, for Kubuntu beginning with 12.10 until 15.04 for Linux Mint and Antergos.
LightDM starts the X servers, user sessions and greeter (login screen).
LXDM is the display manager of LXDE. But it is universal. I (Paiiou) think that it is an excellent manager for Xfce: no dependencies on GNOME or KDE, nice interface, very complete. Most distributions have a package to install. Regarding the configuration, check the presence of a file (or add) /usr/share/xsessions/06xfce4.desktop (the location may differ depending on the distributions), such as:
[Desktop Entry] Encoding=UTF-8 Name=Xfce4 Comment=Use this session to run Xfce4 as your desktop environment TryExec=/usr/bin/startxfce4 Exec=/usr/bin/startxfce4 Icon=/usr/local/share/pixmaps/xfce4_xicon1.png Type=Application
Lines TryExec and Exec may also differ between distributions.
If you installed Xfce system-wide and you want to use the GNOME Display Manager (gdm) to start your Xfce session, you will have to create a .desktop file to teach gdm how to start the Xfce session. This is a sample desktop file, Xfce.desktop:
[Desktop Entry] Encoding=UTF-8 Name=Xfce4 Comment=Use this session to run Xfce 4.4 as your desktop environment Exec=/usr/local/bin/startxfce4 Icon=/usr/local/share/pixmaps/xfce4_xicon1.png Type=Application
It is usually enough to simply copy the example file to the Session directory used by gdm; this directory is usually located in /etc/dm/Sessions, /etc/X11/gdm/Sessions, /usr/share/xsessions, /usr/X11/share/gnome/xsessions or some other location, refer to the documentation of your system for details. You need to restart gdm after you created the file.
If you installed Xfce system-wide and you want to use the KDE Display Manager (kdm) to start your Xfce session, you will have to create a .desktop file to teach kdm how to start the Xfce session.
First you need to find where kdm searches for its .desktop files:
Common locations are /usr/share/apps/kdm/sessions or /usr/local/share/kdm/sessions. Once you found the kdm session directory, you need to create a new file Xfce.desktop with the following:
[Desktop Entry] Encoding=UTF-8 Type=XSession Exec=/usr/local/bin/startxfce4 TryExec=/usr/local/bin/startxfce4 Name=Xfce4 Comment=The Xfce4 Desktop Environment