Docker in docker not running when using official docker dind image

General
1

I am trying to created my own docker image.
In my docker file I used official docker dind image
FROM docker:20.10.7-dind

I install everything else I need inside Dockerfile then create container using that dockerfile and start it.
I shell into it using docker exec -it however when I try to run docker ps or any other command I receive the following error:
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

Should docker already be started if I used dind image? Or I am not understanding this properly.
My CMD to start container is
CMD ["/usr/sbin/sshd", “-D”, “-e”]
because I also want to start ssh server.

How can I start both ssh server and docker so that docker commands can be used inside container?

Thank you.

2

Is it ssafe to assume that the dind container is started with --privliged flag?

3

It is. I run it with the following command:
docker run --privileged dind:latest

4

Did you check the output of ps (literaly, not docker ps) inside the container to check if dockerd is actualy running?

my guess: you override the ENTRYPOINT instruction or your CMD instruction causes the entrypoint script to skip the start of the docker engine inside the container.

5

No it is not running.
ps command outputs:

PID USER TIME COMMAND
1 root 0:00 sshd: /usr/sbin/sshd -D -e [listener] 0 of 10-100 startups
7 root 0:00 bin/bash
36 root 0:00 ps

I also use entryopoint, that is correct.
And if that is true for my entrypoint or CMD, any idea on what to do in order to resolve it?

6

Remove your CMD instruction and verify if my assumption is true. Then you know the problem is within your CMD instruction… I neither use a dind container, nor would I ever (repeat in an endless loop!) run an sshd inside a container.

7

@crodock were you able to figure out the issue ? I’m facing similar issue

8

Hey there, when using docker:cli image you have to bind your host docker.sock to container docker.sock like this

docker run -d -p 22:22 -v /var/run/docker.sock:/var/run/docker.sock my-ssh-image

This option maps the Docker socket file on the host (/var/run/docker.sock ) to the same location inside the container (/var/run/docker.sock ).

10

@crodock, I faced the same problem. This is how I resolved it. In short, I place --init when starting container and I use custom script as the entrypoint.
Dockerfile:

FROM docker:dind
CMD /dump/startup.sh

Create a script file /share/my-folder-with-script/startup.sh that will run sshd and original dockerd-entrypoint.sh:

#!/bin/sh
/usr/sbin/sshd
dockerd-entrypoint.sh

Build image:
docker build -t dockerdev .

Run container:
docker run --init --privileged --name test-container -d -v /share/my-folder-with-script:/dump:ro dockerdev

Inside container you can see the processes:

/ # ps -ef
PID   USER     TIME  COMMAND
    1 root      0:00 {startup.sh} /bin/sh /dump/startup.sh
    7 root      0:00 docker-init -- dockerd --host=unix:///var/run/docker.sock --host=tcp://0.0.0.0:2376 --tlsverify --tlscacert /certs/server/ca.pem --tlscert /certs/server/cert.pem --tlskey /cer
   66 root      0:00 dockerd --host=unix:///var/run/docker.sock --host=tcp://0.0.0.0:2376 --tlsverify --tlscacert /certs/server/ca.pem --tlscert /certs/server/cert.pem --tlskey /certs/server/key.p
   78 root      0:00 containerd --config /var/run/docker/containerd/containerd.toml
  240 root      0:00 sh
  246 root      0:00 ps -ef