How to disable reverse DNS lookup in SSH

SSH server is by default configured to perform reverse DNS lookup of your IP address every time you try to log in to the server. It could slightly improve logging and security, but would significantly increase login time.

Basically the login prompt will take a while to appear as the server will perform reverse DNS lookup prior to presenting the login prompt to the connecting user.

You can fix this issue by disabling the UseDNS directive on the SSH server from the terminal.

1. Launch terminal application.
2. Open SSHd configuration file using a text editor.

   $ sudo vi /etc/ssh/sshd_config
   [sudo] password for user:

3. Search for UseDNS directive and set the value to no.

   UseDNS no

   Add the line if it doesn't already exist and remove the # at the beginning of the line if existing line starts with #.

4. Reload or restart SSH server service.

   $ sudo systemctl restart sshd

   How to start, restart and stop SSH service