I'm trying to installed Docker on a Vagrantbox with Ubuntu 14.04 using the instructions on the official website (Docker Docs). The installation seemed to work, but afterwards I can't start the docker service using sudo service docker start it gives me the following error message:
start: Job failed to start
If I try docker ps -a then I get the following error message:
Cannot connect to the Docker daemon. Is the docker daemon running on this host?
Kernel: Linux vagrant-ubuntu-trusty-64 3.13.0-85-generic #129-Ubuntu SMP Thu Mar 17 20:50:15 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
Relevant lines from /var/log/upstart/docker.log
Waiting for /var/run/docker.sock
Invalid value "" for flag --mtu: strconv.ParseInt: parsing "": invalid syntax
Best Answer
As mentioned by @brent the solution was looking into the logs at
/var/log/upstart/docker.log, which showed that the --mtu parameter was empty. In my case it was dependent on a environment variable that wasn't set.