/usr/share/python3/runtime.d/lightdm-settings.rtupdate is in lightdm-settings 1.1.4-0ubuntu1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | #! /bin/sh
set -e
if [ "$1" = rtupdate ]; then
py3clean -p lightdm-settings /usr/lib/lightdm-settings
py3compile -p lightdm-settings /usr/lib/lightdm-settings
fi
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