[Ubuntu] curl: (6) Could not resolve host

By changing a domain’s DNS I ended up with curl: (6) Could not resolve host issue. I lost a couple of hours before I resolved. The post is all about how resolved the issue.

I recently installed Vanilla forum on TapThatBrain.com. I wanted Vanilla to send out emails when I register users from Vanilla’s dashboard.

The cloud web hosting that I use doesn’t come with a mail server out the box. So I thought of using a SMTP relay service. Using a SMTP relay service demanded changing the domain’s DNS eventually leading me to the issue — curl: (6) Could not resolve host issue.

I took the following approach before I finally resolved the issue.

1. At first, I thought I messed up my nginx configurations. But my configuration was set up to listen both locations — tapthatbrain.com and www.tapthatbrain.com. So my nginx config was good. Did you know? You can use command line to verify if nginx configurations are in place before reloading the nginx server. Learn how.
2. I noticed that when I go to tapthatbrin.com, I was redirected to www.tapthatbrain.com and I wanted to find out where the redirection comes from — nginx, certbot or WordPress. Did you know? You can use curl -I tapthatbrain.com to identify the HTTP response using the command line.
3. The redirection was clearly not from my nginx configuration.
4. WordPress may possibly cause the redirection. The values of WP_HOME and WP_SITEURL in WordPress were www.tapthatbrain.com. But I wasn’t sure if WordPress caused the redirection. So I used WP CLI to update the value to tapthatbrain.com. But the redirection continued to happen.
5. Finally, Certbot’s configuration in nginx made the redirection. In that case I know I should be able to access the website using www.tapthatbrain.com. But I was not able to access using the www version.
6. So, my next thought was the router’s DNS cache. Since I use Jio Fiber connection, I followed the steps listed at https://www.reliancedigital.in/solutionbox/how-to-change-your-dns-to-browse-faster-and-safer/ to clear the DNS cache at router level. But clearing the DNS cache at router level didn’t help.
7. I thought of accessing the both versions (www and the non-www) of the website using a different internet connection. Fortunately, I was able to access both versions using my mobile data.
8. That meant something went wrong at Ubuntu (or system) level. Ubuntu couldn’t resolve the DNS. A quick search on Stack Overflow reveled a solution that worked.

Once I updated the /etc/resolve.conf file, I was able to access both versions of the website tapthatbrain.com from my Ubuntu machine.

This issue could seem naive for someone with decent Ubuntu skills. However, I don’t feel I’m put to shame for sharing this instance. Instead, I see this as learning opportunity.

Today, I’m grateful to all my mentors for all their motivation. They made me stronger each day.