curl: (6) Could not resolve host

What the message looks like

$ curl -I https://shop.example.com
curl: (6) Could not resolve host: shop.example.com

Common causes

• The host name is misspelled, or the record does not exist yet, for example after a new domain, a new subdomain or a DNS migration.
• This machine uses a resolver that fails or has stale data, while others see the record.
• The record exists only in a different zone or in internal DNS, not in public DNS.
• /etc/hosts or a search domain overrides or changes the name.
• The server has no working DNS at all (see “Temporary failure in name resolution”).

Check

1. What does the system resolver say? This is what curl uses
   getent hosts shop.example.comCopy
2. What does public DNS say?
   dig shop.example.com +short @1.1.1.1Copy
3. Do the authoritative servers have the record?
   dig shop.example.com +trace +shortCopy
4. Is there an override in hosts?
   grep -n 'example' /etc/hostsCopy

Fix

• Check the spelling of the host name in the command, the config or the URL.
• If public DNS shows no record, add it at your DNS provider and wait for the TTL of a negative answer to pass.
• If public DNS has the record but only this machine fails, fix the local resolver (resolvectl status) or flush its cache: sudo resolvectl flush-caches.
• If it works with an IP, test with curl --resolve shop.example.com:443:203.0.113.10 https://shop.example.com to separate DNS from the web server.
• Remove wrong lines from /etc/hosts and check the search domain in resolvectl status.

FAQ

dig works but curl does not. Why?

dig asks DNS directly, curl uses the system resolver, which also reads /etc/hosts and uses its own cache. Compare with getent hosts.

How long until a new record works everywhere?

It depends on the TTL and on cached negative answers. See the TTL tool and the post about DNS propagation.