Unable to update Plesk: The 'apt' utility failed to install the required packages

Symptoms

• Plesk is running on a Debian-based server.

• Unable to update Plesk with errors in /var/log/plesk/install/autoinstaller3.log:

  CONFIG_TEXT: Package psa-libxml-proxy is not available, but is referred to by another package.
  This may mean that the package is missing, has been obsoleted, or
  is only available from another source
  E: Version '18.0-v.ubuntu.24.04+p18.0.69.2+t250424.1307' for 'plesk-control-panel' was not found
  E: Unable to locate package sw-engine-cli-7.69:amd64
  .
  .
  .
  Installation will not continue
  ERROR: The 'apt' utility failed to install the required packages.
  Not all packages were installed.
  Visit https://support.plesk.com/ to search for a solution.

• The apt update command fails to execute:

  # apt update 
  Reading package lists... Done 
  E: Could not get lock /var/lib/apt/lists/lock. It is held by process 1508007 (apt-get) 
  N: Be aware that removing the lock file is not a solution and may break your system. 
  E: Unable to lock directory /var/lib/apt/lists/

Cause

There's an apt update process stuck on the server.

Resolution

1. Connect to the Plesk server via SSH.

2. Check the PID for the stuck process:

   # ps aux | grep apt
   ...
   root 393302 0.0 0.1 16504 11008 ? S 2024 36:19 apt-get -qq -y update

   Note: The PID is in the second column. In this example, 393302.

3. Kill the stuck process using the PID retrieved in the previous step. In this example, 393302:

   # kill -9 393302

4. Make sure the following commands run without errors:

   # apt update

   # plesk sbin pum --check

5. Update Plesk.