Bug#774183: lockfile prevents deja-dup from creating new backups

[Guillaume]

Package: deja-dup
Version: 20.2-2.1

Backup consistently fails with the following error:

Another instance is already running with this archive directory
If you are sure that this is the  only instance running you may delete
the following lockfile and run the command again :
    /home/user/.cache/deja-dup/5bdb63923a640aba9a2e3eb735f39192/lockfile.lock

Observed when a scheduled backup starts, and when a backup is started manually.

I checked no other deja-up process is running. I also tried removing
the cache directory (.cache/deja-dup), but the same error occurs at
the next try.

This issues also appears in Ubuntu's bugtracked (found via a Google search).
They apparently even have made a patch for that.
https://bugs.launchpad.net/duplicity/+bug/1266763

  * debian/patches/05-lp1266763-add-concurrency-locking.dpatch
    - Implement locking mechanism to avoid concurrent execution under the same
      cache directory. This functionality adds a dependency to python-lockfile



Guillaume