Did you download the collector from the Releases tab, or are you trying to build the collector locally from sources?
I will create a “normal” installation package that sets the collector up as a service, but that’s not yet done. Downloading the pre-built .jar file from the Releases tab is easier until then, if you are unsure which way to go.
Until there’s a service in place, it’s also recommended to run the collector inside screen to keep it from terminating then the terminal session ends. on a Debian based distribution (like Raspbian or Ubuntu) you can install screen with
sudo apt install screen
After you have installed screen and downloaded the jarfile (at the moment latest version is 0.2), you can start it in a screen with:
screen -S collector java -jar ruuvi-collector-0.2.jar (note that you need to be in the same directory as the .jar file) (the -S flag for screen gives the screen session a human-readable name) you can safely detach the screen session after opening it with Ctrl + A + D. To access the screen later on (for example to see if the collector has printed any logs), you can attach the screen session again with
screen -rd collector (collector is the friendly name of the screen session we started earlier).
Alternatively if you are using a graphical environment, you can just leave a terminal window open there, where you run
java -jar ruuvi-collector-0.2.jar (if you downloaded version 0.2)