Plesk or system update fails on Debian/Ubuntu: Unmet dependencies. Try 'apt --fix-broken install' with no packages

Symptoms

• OS is a Debian/Ubuntu-based distribution.

• Plesk or system update fails with:

  CONFIG_TEXT: The following packages have unmet dependencies:
  <package-name-X> : Depends: <package-name-Y> but it is not going to be installed
  ...
  E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

  CONFIG_TEXT: ERROR: Components and product validation detected at least one important issue:
  Package manager check
  The system package manager reports the following problems:
  The following packages have been unpacked but not yet configured.
  They must be configured using dpkg --configure or the configure
  menu option in dselect for them to work:

• dpkg configuration / audit fails with:

  # dpkg --configure -a
  ...
  dpkg: dependency problems prevent configuration of <package-name-X>:
  <package-name-X> depends on <package-name-Y> (= 7.16.3-2); however:
  Version of imunify360-firewall on system is 7.13.7-1.
  
  dpkg: error processing package <package-name-X> (--configure):
  dependency problems - leaving unconfigured
  
  dpkg: error processing package <package-name-Y> (--configure):
  package is in a very bad inconsistent state; you should
  reinstall it before attempting configuration
  Errors were encountered while processing:
  <package-name-X>
  <package-name-Y>

Cause

Some packages are missing / corrupted or outdated.

Resolution

1. Connect to your Plesk server via SSH.

2. Fix broken package dependencies:

   # apt --fix-broken install

3. Update Plesk:

   # plesk installer update

4. Optional: Install system package updates, if available:

   # apt update && apt upgrade