/etc/lightdm/lightdm.conf.d/91-arctica-greeter-guest-session.conf is in arctica-greeter-guest-session 0.99.0.4-1.
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 9 10 11 12 13 14 15 16 | [LightDM]
# Override default guest-account script by Arctica Greeters guest
# account script.
guest-account-script=arctica-greeter-guest-account-script
[SeatDefaults]
# disable guest sessions (a guest session requires a valid default
# user-session parameter, see below)
allow-guest=true
greeter-allow-guest=true
# if on Ubuntu and Unity is not installed, this is a minimal user session type for
# default (guest) sessions (sudo apt-get install openbox)
#user-session=openbox
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