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

Symptoms

• Plesk update fails on Debian/Ubuntu-based distributions:

  # 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.
  ...
  ERROR: An error occurred on attempt to install packages.
  Attention! Your software might be inoperable.
  Please contact product technical support.
  exit status 1

• Plesk Update Manager reports the following error message:

  # 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 is displayed in Plesk at Tools & Settings > System Updates:

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

Cause

Some packages are half-configured (tagged with F flag):

# dpkg -l | grep '^iF'
iF grub-pc 2.06-3~deb11u6 amd64 GRand Unified Bootloader, version 2 (PC/BIOS version)

This may happen of a previous update was interrupted or hung and several packages are partly installed.

Resolution

1. Connect to the server via SSH.

2. Complete the installation of the half-configured packages:

   # dpkg --configure -a

3. Rerun Plesk/system update.