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 sugges

Answer 1

For the ones who already tried restarting your machine, unsetting the environment variable DOCKER_HOST as told in the docker env documentation and all the rest just try to go with the

sudo service docker restart

Only this did the trick for me even after restarting the machine.

Answer 2

For Ubuntu:
Happened with me when I updated docker.
You need to unmask the service and socket and then restart the service.

Following worked for me:

systemctl unmask docker.service
systemctl unmask docker.socket
systemctl start docker.service

What happend behind the scenes
systemd also has the ability to mark a unit as completely unstartable, automatically or manually, by linking it to /dev/null. This is called masking the unit, and is possible with the mask command.

sudo systemctl mask docker.service

You can check the list of masked services using:

sudo systemctl list-unit-files

To enable auto/manual start of service you need to unmask it using:

sudo sytemctl unmask docker.service

Now the service will be enabled as shown below

Answer 3

Tested in Ubuntu 16.04

# Create the docker group and add your user to the docker group
groupadd docker
usermod -aG docker $USER
newgrp docker

# Configure docker service to be exposed
mkdir -p /etc/systemd/system/docker.service.d
echo -e '[Service]\nExecStart=\nExecStart=/usr/bin/dockerd -H fd:// -H tcp://0.0.0.0:2376' >> /etc/systemd/system/docker.service.d/override.conf

# restart service
systemctl daemon-reload
service docker restart

Answer 4

You need to add your current user to the docker group as follows:

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

After install everything and start the service, try close your terminal and open it again, then try pull your image

Edit

I also had this issue again, if the solution above won't worked, try this solution that is the command bellow

sudo mv /var/lib/docker/network/files/ /tmp/dn-bak

---

Considerations

If command above works you probably are with network docker problems, anyway this resolves it, to confirm that, see the log with the command bellow

tail -5f /var/log/upstart/docker.log

If the output have something like that

FATA[0000] Error starting daemon: Error initializing network controller: could not delete the default bridge network: network bridge has active endpoints 
/var/run/docker.sock is up

You really are with network problems, however I do not know yet if the next time you restart(update, 2 months no issue again) your OS will get this problem again and if it is a bug or installation problem

My docker version

Client:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.4.2
 Git commit:   a34a1d5
 Built:        Fri Nov 20 13:12:04 UTC 2015
 OS/Arch:      linux/amd64

Server:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.4.2
 Git commit:   a34a1d5
 Built:        Fri Nov 20 13:12:04 UTC 2015
 OS/Arch:      linux/amd64