How do I clear the DNS cache?

Solution 1:

Ubuntu 17.04 and higher (18.04)

From Ubuntu 17.04 and onwards, systemd-resolve is used for DNS. You can flush systemd's caches like so:

sudo systemd-resolve --flush-caches

Solution 2:

For 18.04 and higher

Look at Mike Shultz' answer.

For 11.10 and below

Ubuntu doesn't cache dns records by default so unless you've installed a dns cache there isn't anything to clear.

DNS records are likely cached by your provider's DNS servers so if you want to check if the DNS changes you made were successful you can interrogate a DNS server from your domain hosting service with dig:

dig -t a ns1.myhostingcompany.com @domain_registrar_dns_server

It you want Ubuntu to start caching dns I recommend installing pdnsd together with resolvconf. nscd is buggy and not advisable.