How to Flush DNS Cache in Ubuntu 20.04, 21.10 via Systemd

Make DNS change regularly and want to flush DNS cache in Ubuntu? Well, this simple tutorial is going to show you how to do it in Ubuntu 20.04, Linux Mint 20, Ubuntu 21.10 via systemd.

1. First open terminal from system application menu or get into command console for your remote Ubuntu Server.
Then run command:

sudo systemd-resolve --flush-caches

You can then run command to verify that the caches have been emptied:

systemd-resolve --statistics

And you’ll see something that says “Current Cache Size: 0”:

DNSSEC supported by current servers: no

Transactions              
Current Transactions: 0   
  Total Transactions: 2900
                          
Cache                     
  Current Cache Size: 0   
          Cache Hits: 1526
        Cache Misses: 1653
                          
DNSSEC Verdicts           
              Secure: 0   
            Insecure: 0   
               Bogus: 0   
       Indeterminate: 0

2. If you’re running dnsmasq, just run command to restart the service which will also clear the DNS cache:

sudo systemctl restart dnsmasq

And if you want to check out the statistics, run command to dump to system log:

sudo pkill -USR1 dnsmasq

Then consult the system logs via command:

sudo tail /var/log/syslog

That’s it. Enjoy!