/usr/share/xsessions/Lubuntu-Netbook.desktop is in lubuntu-default-settings 0.27.
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 | [Desktop Entry]
# The names/descriptions should really be better
Name=Lubuntu Netbook
Comment=Lubuntu Netbook - Lightweight X11 desktop environment based on LXDE
Exec=/usr/bin/startlubuntu-netbook
# Icon=
Type=Application
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