In case, you
only need to write "jack_capture", and thats it, the --port
argument is not necessary. Please also write why you felt the need to
use the --port argument, I probably have to change the documentation.
In case not, please post the complete output from the terminal,
including the command you used to start jack_capture.
david@eurolap:~$ jack_capture
No valid ports selected.
david@eurolap:~$
Thats actually impossible. :-)
Maybe you are starting an older version of jack_capture?
Which version of jack_capture did you install from RPM?
Please also try "type -a jack_capture" and
"/usr/local/bin/jack_capture".