How to turn off Software updater? (Xubuntu)

One of the easiest way I did to overcome from this problem is that you can remove update-notifier

sudo apt-get remove update-notifier

Please note that, this will remove only the graphic way to do system updates.. You can still do your upgrades using commands or Synaptic :)

You can always reply if you get in any trouble.. :)

Go to Settings > Session and Startup > App Autostart and uncheck Update Notifier. Also make sure that no other similar entry (like Synaptic) is enabled in that list. Take note that this will likely disable the automatic updating of the data from the package repositories.

Alternative CLI solution:

sudo crudini --set /etc/xdg/autostart/update-notifier.desktop 'Desktop Entry' Hidden true;

If you need crudini, then: sudo pip install crudini