Hi. What is happening is what is described by the other posters above.
Specifically, on Ububtu (in my case 16), the elasticsearch init script (ie typing 'systemctl start elasticsearch' from a shell) does not start elasticsearch. It returns '[OK]', but elasticsearch does not start. It gives no error message and leaves no logs. It is therefore very difficult to debug, know where to start, or give any useful feedback.
As others have posted, running this command from a shell will successfully launch elasticsearch for me:
sudo -u elasticsearch /usr/share/elasticsearch/bin/elasticsearch -d -p /var/run/elasticsearch/elasticsearch.pid --default.config=/etc/elasticsearch/elasticsearch.yml --default.path.home=/usr/share/elasticsearch --default.path.logs=/var/log/elasticsearch --default.path.data=/var/lib/elasticsearch --default.path.work=/tmp/elasticsearch --default.path.conf=/etc/elasticsearch
So it would seem that the init script is broken. Since it gives no output, it is difficult to debug, but I will attempt to do so today.
My suspicion is that it makes wrong assumptions about its environment, since I'm guessing it works on some distros, for example it worked for you.