Docker command can't connect to Docker daemon

Question

I want to make a move to Docker, so I've just started to mess around with it. I've installed Docker on a VirtualBox Ubuntu 15.10 (Wily Werewolf) installation and as suggested here I then tried running a basic nginx Docker image:

$ docker run --name mynginx1 -P -d nginx
Cannot connect to the Docker daemon. Is the docker daemon running on this host?

So I checked out whether Docker was running:

$ sudo service docker status
● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since vr 2015-11-06 08:41:48 CET; 15min ago
     Docs: https://docs.docker.com
 Main PID: 7542 (docker)
   CGroup: /system.slice/docker.service
           └─7542 /usr/bin/docker daemon -H fd://

nov 06 08:41:47 kramer65-VirtualBox systemd[1]: Starting Docker Application Container Engine...
nov 06 08:41:47 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:47.900410966+01:00" level=info msg="API ...ock"
nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.033514149+01:00" level=info msg="Fire...lse"
nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.141594321+01:00" level=info msg="Defa...ess"
nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.416294436+01:00" level=warning msg="Y...it."
nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.565507576+01:00" level=info msg="Load...rt."
nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.567907022+01:00" level=info msg="Load...ne."
nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.567945214+01:00" level=info msg="Daem...ion"
nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.567969891+01:00" level=info msg="Dock....9.0
nov 06 08:41:48 kramer65-VirtualBox systemd[1]: Started Docker Application Container Engine.
Hint: Some lines were ellipsized, use -l to show in full.

This suggests that the Docker daemon is actually already running, but to be sure I just started the Docker daemon manually:

$ sudo docker daemon
INFO[0000] API listen on /var/run/docker.sock           
INFO[0000] [graphdriver] using prior storage driver "aufs" 
INFO[0000] Firewalld running: false                     
INFO[0000] Default bridge (docker0) is assigned with an IP address XXX.XX.X.X/XX. Daemon option --bip can be used to set a preferred IP address 
WARN[0000] Your kernel does not support swap memory limit. 
INFO[0000] Loading containers: start.                   

INFO[0000] Loading containers: done.                    
INFO[0000] Daemon has completed initialization          
INFO[0000] Docker daemon                                 commit=76d6bc9 execdriver=native-0.2 graphdriver=aufs version=1.9.0

I then tried running the image again, but with the same result:

$ docker run --name mynginx1 -P -d nginx
Cannot connect to the Docker daemon. Is the docker daemon running on this host?

I tried sudo'ing the command, but to no avail. What am I doing wrong here?

Answer 1

I have same issue while running docker.

you can run commands as sudo user:

sudo docker ***your command here***

Answer 2

enter as root (sudo su) and try this:

unset DOCKER_HOST
docker run --name mynginx1 -P -d nginx

I've the same problem here, and the docker command only worked running as root, and also with this DOCKER_HOST empty

PS: also beware that the correct and official way to install on Ubuntu is to use their apt repositories (even on 15.10), not with that "wget" thing.

Answer 3

Giving non-root access - from docker

Add the docker group if it doesn't already exist.

$ sudo groupadd docker

Add the connected user "${USER}" to the docker group.

Change the user name to match your preferred user.

You may have to logout and log back in again for this to take effect.

$ sudo gpasswd -a ${USER} docker

Restart the Docker daemon.

$ sudo service docker restart

Answer 4

You need to add your current user [suppose you're logged in as ubuntu] to docker group as follow

sudo usermod -aG docker $(whoami)

then logout & login again into the system or restart the system. test by docker version

for further info how to install docker-engine follow docker documentation

Answer 5

Try to use "sudo" with the command you are running.

Answer 6

For OSX:

After opening docker and starting the 'default' machine via the Quickstart Terminal (https://docs.docker.com/engine/installation/mac/), you try docker commands and get this "can't connect to docker daemon" message, it turns out you need some env variables set:

eval "$(docker-machine env default)"

Then try it out with docker run hello-world to see if everything is peachy.