The server can be debugged by using either the -d or -D option.
The -d option launches the server to one-shot mode. In this mode, the server accepts only one connection and exits after the session is disconnected. The server does not spawn a separate task for the connection.
The -D option launches the server to continuous debug mode. In this mode, the server keeps on listening to the TCP port and accepts several connections. The server spawns new task for each new connection and needs to be stopped manually when you want to finish the debugging.
The debug level is either a number, or a comma-separated list of assignments of the format ModulePattern=debug_level, for example "*=7,sshd2=2". Debug level 4 is usually sufficient. For more detailed information, debug level 7 can be used.