To make sure that an FTP client does not timeout when connected to a ProFTPD server, you can modify the TimeoutIdle directive in the server's configuration file.
The TimeoutIdle directive specifies the maximum number of seconds that an idle connection will be allowed to remain open. If the client does not send any data or request within this time, the server will close the connection.
To increase the idle timeout, you can set the TimeoutIdle directive to a higher value. For example, to set the idle timeout to 10 minutes, you can add the following line to the proftpd.conf configuration file:
TimeoutIdle 600
You'll need to restart the ProFTPD server for the change to take effect. You can do this using the following command:
systemctl restart proftpd
Keep in mind that increasing the idle timeout may have an impact on server performance, as it will keep idle connections open for a longer period of time. It's a good idea to balance the need for a longer idle timeout with the need to maintain good server performance.