Can't run the launcher to install Discourse on CentOS 7

try
systemctl start docker.service

「いいね!」 3

In case anyone finds it handy in future:

On CentOS 7 try linking the non-existent docker.io binary to the existing docker binary as follows:
ln -s /usr/bin/docker /usr/bin/docker.io

This did it for me just now…

「いいね!」 1

Worked. Somehow this should come up as the right answer.

「いいね!」 1

Exactly. If it says docker isn’t running, just do a service docker start and move on. That’s what I did.