pls read
http://docs.pgbarman.org/release/2.3/#show-serverfor "barman show-server" it states:
barman show-server <server_name>
1. move your barman.conf back to /etc/
2. within /etc/barman/ you'll find some example conf files which have to be copied and modified to fit to your environment.
I assume you want to configure streaming backup for a pg-cluster?
So make a copy of the streaming example and put your values here.
The file should be named e.g. like your cluster. We (at work) use servername_port.conf and <server_name> refers ALWAYS to the names of such conf files within /etc/barman/ .
To summarize:
/etc/barman.conf holds general settings for barman itself and defaults for configured servers
/etc/barman/yourservername.conf contains server specific settings and may also overrule values from /etc/barman.conf (like Retention period, binary path a.s.o.
The command should then looks like
barman show-server yourservername
hope it helps
regards Georg