See session log below:

+ roundup-server -n hipnosi.net -p 8081 -l
/var/log/roundup-server -d /var/run/roundup.pid -u 102
-g 103 hipnosi=/var/roundup/trackers/hipnosi
Error: exceptions.ValueError: Group 103 doesn't exist

[... usage message ommitted ...]

[root@fedora init.d]# id -g roundup
103