Often enough I run into this little problem: I make a DNS change and want to see the results. When I check for the changes though it looks as if nothing has changed, and sometimes this is caused by my system’s DNS cache.
Clearing the cache on Ubuntu 20.04 can be done with the following command:
sudo systemd-resolve --flush-caches, you can verify that the caches have been emptied by following that up with the command
systemd-resolve --statistics which then gives an output like shown below:
DNSSEC supported by current servers: yes Transactions Current Transactions: 0 Total Transactions: 21870 Cache Current Cache Size: 0 Cache Hits: 6722 Cache Misses: 15158 DNSSEC Verdicts Secure: 7783 Insecure: 21703 Bogus: 0 Indeterminate: 0
The text and numbers will vary per setup, the “Current Cache Size” should however display a value of 0 to indicate your cache has been cleard.
If you are running dnsmasq next to the standard systemd-resolve like I do, restarting dnsmasq (with
sudo systemctl restart dnsmasq) will ensure its caches are cleared to (otherwise you may still end up getting cached results).