I have just started using Duplicati and I must say it is really useful. A few things I have questions about are that when I have run test back ups of system and or program files that are in use when the backing up is being performed I will see warnings and sometimes error mesages when that test back up has completed itself.
Sorry I did not realize that I needed to turn on Live logging for warnings and errors first as when I returned to the logs they were no longer there to copy and paste to this post.
If you run it under Windows, try to set up Duplicati as a service; you can then set the ‘snapshot-policy’ advanced option to something else than ‘off’ and it will allow it to backup files when they are in use. Another possibility is to add exclusion filters to your backup to remove files that are always in use for every backup (such as the Duplicati database for example)
a limited number of warnings are kept in the job logs (select the job and click ‘logs’). You can extract them from there.
Duplicati Tutorial 02 Install Duplicati as a Service is kind of old, but a helpful intro to that plan.
Alternatively, Windows will let an elevated (maybe UAC prompt) administrator use snapshots.
If you start Duplicati from a shortcut, you can right-click → Properties → Advanced and check Run as administrator. This is more trouble but has advantages, e.g. Tray Icon is set to go.