Tasks in Plesk are never executed and stuck as new: Cannot fetch process properties

Symptoms

• Various tasks in Plesk are never executed, their status in the menu Tools & Settings > Task Manager is stuck in "new".

• The following error can be found in the log file /var/log/plesk/task-manager.log:

  ERROR Cannot fetch process properties: Cannot fetch 'run-plesk-task-93137.service' unit properties: dbus: connection closed by user
  

Cause

The service dbus.socket is stuck.

Resolution

1. Connect to the server via SSH.

2. Restart services dbus.socket and plesk-task-manager:

   # systemctl restart dbus.socket plesk-task-manager

Warning: in Debian 10 or Ubuntu 18.04, there might be the service polkit, which also should be up and running. Restart it using the command systemctl restart polkit in case the issue persists on these operating systems.