/usr/share/xsessions/cairo-dock.desktop is in cairo-dock-data 3.4.1-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | [Desktop Entry]
Name=Cairo-Dock (GNOME)
Comment=This session logs you into GNOME with Cairo-Dock
Exec=gnome-session --session=cairo-dock
TryExec=gnome-session
Icon=
Type=Application
DesktopNames=Unity
|