Cannot connect to the Docker daemon on Debian

Question

I try to execute docker run hello-world on a debian bullseye machine where I do not have root user rights, but where I can use sudo.

I installed docker (v19.03.13) with sudo according to the docker documentation. docker can be started using sudo systemctl start docker and according to sudo systemctl status docker the service is running as expected. As well sudo systemctl status docker.socket looks normal.

I found a docker.sock file at /var/run/.

Now, when try to run docker run hello-world (no sudo!) I get an error message:

docker: Cannot connect to the Docker daemon at unix:///home/<myuser>/.docker/run/docker.sock. Is the docker daemon running?.

So as it seems, the docker service is looking in the wrong directory for docker.sock.

The following things I tried already, but didn't work:

• sudo systemctl stop/start/restart docker(standard answer I found in discussions about this problem)
• added my user to docker group: sudo usermod -aG docker $USER. Command less /etc/group | grep docker yields docker:x:999:myUserName
• ls -la /var/run/docker.sock--> srw-rw---- 1 root docker 0 Jul 17 17:48 /var/run/docker.sock (suggested by https://unix.stackexchange.com/a/279785/335075)
• unset DOCKER_HOST (e.g. https://stackoverflow.com/a/69674630/1552080).
• sudo mount -t cgroup -o none,name=systemd cgroup /sys/fs/cgroup/system (this worked once, but not a second time after I logged out an in again)

What I can do is run sudo docker run hello-world.

Answer 1

It sounds like you have somehow setup an alternative docker context for your user. Perhapse you were experimenting with installing docker another way or have inadvertatly typed something.

You can check this with

$ docker context ls
NAME        DESCRIPTION                               DOCKER ENDPOINT               ERROR
default *  

---

Docker documentation includes instructions for both creating a new context and selecting a context:

$ docker context create docker-test --docker host=tcp://docker:2375
docker-test
Successfully created context "docker-test"

$ docker context use docker-test
docker-test
Current context is now "docker-test"

Answer 2

Finally, I found the root cause to this problem. I found an entry in .bashrc explicitly setting the path for docker.sock

Found in .bashrc:

# Docker rootless configuration
export XDG_RUNTIME_DIR=/home/<myusername>/.docker/run
export PATH=$PATH:/sbin
export DOCKER_HOST=unix:///home/<myusername>/.docker/run/docker.sock

Changed to

# Docker rootless configuration
export XDG_RUNTIME_DIR=/var/run
export PATH=$PATH:/sbin
export DOCKER_HOST=unix:///var/run/docker.sock

I don't know if this causes other problems, but at first glance it spares me from unset DOCKER_HOST at logging in.