Plesk Premium Antivirus for Servers (Dr.Web) fails to start: A path to a valid license key file was not specified

Symptoms

Plesk Premium Antivirus fails to start with the following error:

# service drwebd start
Starting Dr.Web drwebd...
Dr.Web (R) daemon for Linux/Plesk Edition v6.0.2.9
Copyright (c) Igor Daniloff, 1992-2025
Doctor Web, Moscow, Russia
Support service: http://support.drweb.com
To purchase: http://buy.drweb.com
Key file: /opt/drweb/drweb32.key - Key file was not found! (No such file or directory)
A path to a valid license key file was not specified.
Plesk authorization failed: HTTP request error [35]
Error: Plesk Software not running.

Cause

Plesk Premium Antivirus is a paid service that requires a license, but no license has been purchased.

Resolution

Purchase and install a Plesk Premium Antivirus license: https://www.plesk.com/extensions/offer-premium-av/