TOPIC: TRANSPORT LAYER SECURITY
Adding a new domain or subdomain to an SSL certificate using Certbot
11th June 2025On 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.
Manually updating Let's Encrypt certificates
8th November 2024Normally, Let's Encrypt certificates get renewed automatically. Thus, it came as a surprise to me to receive an email telling me that one of my websites had a certificate that was about to expire. The next step was to renew the certificate manually.
That sent me onto the command line in an SSH session to the Ubuntu server in question. Once there, I used the following command to check on my certificates to confirm that the email alert was correct:
sudo certbot certificates
Then, I issued this command to do a test run of the update:
sudo certbot renew --dry-run
In the knowledge that nothing of concern came up in the dry run, then it was time to do the update for real using this command:
sudo certbot renew
Rerunning sudo certbot certificates checked that all was in order. All that did what should have happened automatically; adding a cron job should address that, though, and adding the --quiet switch should cut down on any system emails too.
Dealing with the following message issued when using Certbot on Apache: "Unable to find corresponding HTTP vhost; Unable to create one as intended addresses conflict; Current configuration does not support automated redirection"
12th April 2024When doing something with Certbot on another website not so long ago, I encountered the above message when executing the following command (semicolons have been added to separate the lines):
sudo certbot --apache
The solution was to open /etc/apache2/sites-available/000-default.conf using nano and update the ServerName field (or the line containing this keyword) so it matched the address used for setting up Let's Encrypt SSL certificates. The mention of Apache in the above does make the solution specific to this web server software, so you will need another solution if you meet this kind of problem when using Nginx or another web server.