How can I see systemd-resolve dns cache?

Question

Using sudo systemd-resolve --statistics let me see the current dns cache statistics, for example :

Cache                     
  Current Cache Size: 68  
          Cache Hits: 412 
        Cache Misses: 461

I would like to see all the entries of the dns cache (here 68), is it possible?

Solution

As mentioned by bac0n, you can use the following command to send signal USR1 to systemd-resolved:

sudo killall -USR1 systemd-resolved

This will NOT stop the service. It just tells systemd-resolved to write all the current cache entries (and some other information) to the system log.

You can then export the log messages written by systemd-resolved to a text file with the following command:

sudo journalctl -u systemd-resolved > ~/resolved.txt

Open the text file generated this way in the text editor of your choice and search for CACHE:. After this the list of cache entries will follow.

Please note that the text file might contain several CACHE:.

Comments

[bac0n]

think you can do: killall -USR1 systemd-resolved (the output will be redirected to journald)

[johhnry]

But this is going to kill the process rather than printing the cache?

[bac0n]

no, it wil just sending SIGUSR1 to systemd-resolved, you can find a description in man systemd-resolved

[johhnry]

Thanks a lot, this is helpful!