Technology Tales

Adventures in consumer and enterprise technology

TOPIC: KEY MANAGEMENT

Adding a new domain or subdomain to an SSL certificate using Certbot

11^th June 2025

On checking the Site Health page of a WordPress blog, I saw errors that pointed to a problem with its SSL set up. The www subdomain was not included in the site's certificate and was causing PHP errors as a result, though they had no major effect on what visitors saw. Still, it was best to get rid of them, so I needed to update the certificate as needed. Execution of a command like the following did the job:

sudo certbot --expand -d existing.com -d www.example.com

Using a Let's Encrypt certificate meant that I could use the certbot command, since that already was installed on the server. The --expand and -d switches ensured that the listed domains were added to the certificate to sort out the observed problem. In the above, a dummy domain name is used, but this was replaced by the real one to produce the desired effect and make things as they should have been.

The content, images, and materials on this website are protected by copyright law and may not be reproduced, distributed, transmitted, displayed, or published in any form without the prior written permission of the copyright holder. All trademarks, logos, and brand names mentioned on this website are the property of their respective owners. Unauthorised use or duplication of these materials may violate copyright, trademark and other applicable laws, and could result in criminal or civil penalties.

All comments on this website are moderated and should contribute meaningfully to the discussion. We welcome diverse viewpoints expressed respectfully, but reserve the right to remove any comments containing hate speech, profanity, personal attacks, spam, promotional content or other inappropriate material without notice. Please note that comment moderation may take up to 24 hours, and that repeatedly violating these guidelines may result in being banned from future participation.

By submitting a comment, you grant us the right to publish and edit it as needed, whilst retaining your ownership of the content. Your email address will never be published or shared, though it is required for moderation purposes.