System update shows warning on Plesk server: Target Packages (...) is configured multiple times in /etc/apt/sources.list.d/plesk-ext-panel-migrator.list

Symptoms

• Package updates lead to the multiple warnings by apt-get:

  # apt-get update
  ...
  Reading package lists... Done
  W: Target Packages (all/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/plesk-ext-panel-migrator.list:1 and /etc/apt/sources.list.d/plesk-ext-site-import.list:1
  W: Target Packages (all/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/plesk-ext-panel-migrator.list:1 and /etc/apt/sources.list.d/plesk-ext-site-import.list:1

• Plesk has both Plesk Migrator and Site Import extensions installed at Extensions > My Extensions.

Cause

This is a Plesk bug #PMT-4794 which is planned to be fixed in future product updates.
It is caused by the fact that both extensions add the same repository in the list so it leads to the duplication.

Resolution

These warnings can be safely ignored.

Warning: Removing repository files .list at /etc/apt/sources.list.d/ is not recommended as Plesk needs both.