server config, <VirtualHost>, <Global>
1.2.10rc2 and later
The TimeoutLinger directive configures the maximum number of seconds that proftpd will wait (or "linger") when closing a data connection. Once the data connection is closed, proftpd will send a message on the control connection indicating the closure. This delay is necessary for properly handling some FTP clients.
If the client aborts a transfer and there is a long delay, this lingering close is the most likely culprit. So if you encounter this delay, set TimeoutLinger to a low number to remove the delay.