Plesk update on Debian or Ubuntu fails: E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem

Symptoms

Note: This article is applicable only to Plesk servers with Debian or Ubuntu operating systems.

• Plesk update on Debian or Ubuntu fails:

  # plesk installer update --repatch
  ..........
  E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem.
  Plesk is down, performing full restart.
  Starting sw_engine service... done
  Starting sw_cp_server service... already started
  Starting mysql service... already started
  
  ERROR: An error occurred on attempt to install packages.
  Attention! Your software might be inoperable.
  Please contact product technical support.
  exit status 1

  Or 'pum' check fails:

  # plesk sbin pum --check
  INFO: pum is called with arguments: ['--check']
  E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem.
  ERROR: Exited with returncode 100.
  exit status 100

• The error below may appear in the menu Tools & Settings > System Updates:

  PLESK_ERROR: The System Updates tool is already installing updates in automatic mode. Please try later.

Cause

Previous update installation attempt was interrupted or hung and several packages are partly installed.

Resolution

1. Connect to the server using SSH.

2. Complete the installation of the partially installed packages:

   # dpkg --configure -a

3. If the error was in the menu Tools & Settings > System Updates,  complete the packages update there; if it is in Plesk Installer on updating Plesk, install latest Plesk updates:

   # plesk installer --select-release-latest --upgrade-installed-components