Plesk scheduled backup fails: Failed to open file ‘/var/lib/psa/dumps/.run’

Symptoms

The following error occurred during the scheduled backup process:

pmm-ras failed (Error code = 1): Failed to open file '/var/lib/psa/dumps/.run': Is a directory

Cause

There are custom files in /var/lib/psa/dumps with .xml extension which prevent backup from running.
This behavior is considered as a bug with ID PPPM-12328.

Resolution

Until the bug is fixed:

1. Connect to the server via SSH.

2. Move non-Plesk related .xml files from /var/lib/psa/dumps/ to somewhere else. For example to root ./ directory:

   # mv /var/lib/psa/dumps/custom.xml ./

3. Wait for the next scheduled backup task to run.