Docker-Compose can't connect to Docker Daemon

Question

I am getting an error message saying I can't connect to the docker daemon. I have looked into other people's answers who have had similar issues but it hasn't helped. I am running the version of Ubuntu 15.10. I will try to provide all the info I have.

root@# docker-compose -f docker-compose-deps.yml up -d
ERROR: Couldn't connect to Docker daemon at http+docker://localunixsocket - is it running?

If it's at a non-standard location, specify the URL with the DOCKER_HOST environment variable.

Docker Version

root@# sudo docker     version
Client:
Version:      1.9.1
API version:  1.21
Go version:   go1.4.2
Git commit:   a34a1d5
Built:        Fri Nov 20 13:20:08 UTC 2015
OS/Arch:      linux/amd64
Cannot connect to the Docker daemon. Is the docker daemon running on this host?

Docker-Compose Version

root@# docker-compose --version
docker-compose version 1.5.2, build 7240ff3

This is what happens if I try to stop or start the service...

root@# sudo service docker stop
stop: Unknown instance: 
root@# sudo service   docker start
docker start/running, process 5375

If I run ps aux | grep docker

root@# ps aux | grep docker
root      4233  0.0  0.0  13692  2204 pts/15   S+   10:27   0:00 grep --color=auto docker

Any help would be greatly appreciated. Let me know if you may need anymore information.

Answer 1

I had the same issue. After taking notes and analyzing some debugging results, finally, I solved what can be the same error. Start the service first,

service docker start

Don't forget to include your user to the docker group.

Answer 2

From the output of "ps aux | grep docker", it looks like docker daemon is not running. Try using below methods to see what is wrong and why docker is not starting

1. Check the docker logs

$ sudo tail -f /var/log/upstart/docker.log

2. Try starting docker in debug mode

$ sudo docker -d -D

Answer 3

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.