What does this warning signify?

[JonMikelV]

@gctwnl

Expected there to be a temporary fileset for synthetic filelist

Usually it signifies Duplicati got interrupted in some way during a previous backup but isn’t usually anything to be concerned about.

Here are two posts that explain it a little more:

Irritating error message

A synthetic filelist is a list of files that Duplicati creates after it has been interrupted, in an attempt to give access to as much as possible. The synthetic filelist is used by taking the previous file list, and adding/updating new files where data was successfully uploaded. It does not remove files, and it is not a real disk-snapshot, hence the name “synthetic”. The warning is that Duplicati expected the code to generate a synthetic filelist and mark it temporary (i.e. in-progress), but n…

How does Duplicati Resume After Interruption?

Duplicati uses SQLite to provide transactional storage, meaning it will either be written completely or not at all. It keeps track of all remote files and will generally be able handle everything nicely. It marks all files “uploading” when they are in-progress, “uploaded” when they are reported as completed, and “verified” when they have been seen in a file listing. If you interrupt it, the next run will look at all “uploading” files and check if they have the full length as it expects, and i…