Docker-Compose can't connect to Docker Daemon

I had the same error, after 15 min of debugging. Turns out all it needs is a sudo :)

Check out Create a Docker group to get rid of the sudo prefix.

I had this problem and did not want to mess things up using sudo. When investigating, I tried to get some info :

docker info

Surprinsingly, I had the following error :

Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http:///var/run/docker.sock/v1.38/info: dial unix /var/run/docker.sock: connect: permission denied

For some reason I did not have enough privileges, the following command solved my problem :

sudo chown $USER /var/run/docker.sock

Et voilà !

It appears your issue was created by an old Docker bug, where the socket file was not recreated after Docker crashed. If this is the issue, then renaming the socket file should allow it to be re-created:

$ sudo service docker stop
$ sudo mv /var/lib/docker /var/lib/docker.bak
$ sudo service docker start

Since this bug is fixed, most people getting the error Couldn't connect to Docker daemon are probably getting it because they are not in the docker group and don't have permissions to read that file. Running with sudo docker ... will fix that, but isn't a great solution.

Docker can be run as a non-root user (without sudo) that has the proper group permissions. The Linux post-install docs has the details. The short version:

$ sudo groupadd docker
$ sudo usermod -aG docker $USER
# Log out and log back in again to apply the groups
$ groups  # docker should be in the list of groups for your user
$ docker run hello-world  # Works without sudo

This allows users in the docker group to run docker and docker-compose commands without sudo. Docker itself runs a root, allowing some attacks, so you still need to be careful with what containers you run. See Docker Security Documentation for more details.