I went further on:
I created a mattermost.service within the systemd. The following link was helpful
http://zwarag.com/2015/10/how-to-use-systemd-to-run-the-mattermost-chat-platform/
After a reboot I checked whether the service was started, but wasn´t.
I found on github a similar issue, where was a problem with the user rights
For a test I changed the User in the mattermost.service file to root … and it works.
So finally: use the systemd file and fix the user rights and the problem is solved 