As documented in https://logback.qos.ch/manual/configuration.html

You can specify a particular config file like this:

You may specify the location of the default configuration file with a system property named"logback.configurationFile". The value of this property can be a URL, a resource on the class path or a path to a file external to the application.

java -Dlogback.configurationFile=/path/to/config.xml chapters.configuration.MyApp1

If you don’t want to override the whole file, but just want to be able to set debug level just by setting a system, then see my answer here: http://stackoverflow.com/a/5884505/191084

Thanks

David