Ubuntu - Networking - DNS - Check DNS Cache

resolvectl statistics
 
or
 
systemd-resolve --statistics

returns:

DNSSEC supported by current servers: no
 
Transactions              
Current Transactions: 0   
  Total Transactions: 1163
 
Cache                     
  Current Cache Size: 33  
          Cache Hits: 879 
        Cache Misses: 284 
 
DNSSEC Verdicts           
              Secure: 0   
            Insecure: 0   
               Bogus: 0   
       Indeterminate: 0

NOTE: The Current Cache Size is the value you're looking for.

If it's 0, you just flushed the DNS cache.

The cache can store up to 4096 DNS responses for up to 2 hours, so don’t expect to see a massive number listed as the current cache size.

The DNS cache can’t grow to more than 420 kB when used to its fullest; so no concern about memory usage.