Then sudo systemctl start logstash will start Logstash as a service (in background = run forever) using default config file which should be /etc/logstash/conf.d/logstash.conf.
That is another question... Do you really need more than one?
I guess you can create several SystemD unit files that use different config files. That is what I used to do for Elasticsearch.
So far I have been able to get by with just one Logstash config. It is getting a bit long with close to 20 different inputs and plenty of conditionals in the filter section.
Then there are Logstash pipelines that might help you.
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