I use Ubuntu 16.04.1 LTS. I have also installed Xfce4 so in Lightdm login screen I can choose Unity or Xfce. I assume that when Lightdm runs Xfce4 desktop environment it uses /usr/bin/startxfce4 Then Xfce runs a dedicated window manager Xfwm4. A configuration file is stored here:
/etc/xdg/xfce4/xfconf/xfce-perchannel-xml/xfce4-session.xml
Xfce can be used with other window manager, here is a configuration option from that file:
<property name="Client0_Command" type="array">
<value type="string" value="xfwm4"/>
</property>
I wonder how Lightdm starts Unity/Compiz ? Unity is a Compiz plugin and can't be used with other window manager, right ? So how exactly Lightdm runs Compiz?
Compiz can be run with parameters, for example:
compiz --replace ccp (a configuration plugin which can load other plugins)
or
compiz --replace composite opengl etc. (a plugin list is defined explicitly)
Update
lightdm-session runs gnome-session --session=ubuntu, gnome-session refers to /usr/share/gnome-session/sessions/ubuntu.session. Here is my ubuntu.session content:
[GNOME Session]
Name=Ubuntu
RequiredComponents=unity-settings-daemon;
DesktopName=Unity
There is nothing about Compiz. So probably /usr/bin/unity is run and it load some other config?
