This applies to a 16.04 Lubuntu system.
There's this related question How to prevent deja-dup-monitor from running, or completely delete it? but that user didn't use deja-dup and just wanted to kill it. Also something about a weird interaction with Google Chrome, also not my issue.
I use deja-dup but only on demand. I don't need its daemon running to kick off automatic backups.
I've killed the daemon and tested backups and restores with it dead and they work fine.
sudo systemctl stop deja-dup-monitor
but I get
Failed to stop deja-dup-monitor.service: Unit deja-dup-monitor.service not loaded.
though it shows up in Task Manager
sudo systemctl disable deja-dup-monitor results in
Failed to execute operation: No such file or directory
How can I prevent deja-dup-monitor from starting?