How to create log files with QIS?

To turn on log mode in QIS, pass -portlog as the command line option when launching QIS.

The log file, qis.log_0, will be created in the startup directory or the directory set 
via Set_Working_Directory of QIS when a client connects to QIS.  If a second client 
connects to the same QIS, another log file qis.log_1 will be created; a separate log 
file per connection.  Once the log file is created, it will not be moved even if the 
working directory is changed via Set_Working_Directory.