Jenkins user using docker (inside docker container) - jenkins

Question

I have a dockerfile:
FROM jenkins:1.651.1
COPY plugins.txt /usr/share/jenkins/plugins.txt
RUN /usr/local/bin/plugins.sh /usr/share/jenkins/plugins.txt
USER root
RUN groupadd docker
RUN usermod -a -G docker jenkins
USER jenkins
I add my user jenkins to the group docker.
When I access my container:
jenkins#bc145b8cfc1d:/$ docker ps
Cannot connect to the Docker daemon. Is the docker daemon running on this host?
jenkins#bc145b8cfc1d:/$ whoami
jenkins
This is the content of my /etc/groupon my container
jenkins:x:1000:
docker:x:1001:jenkins
my jenkins user is in the docker group
jenkins#bc145b8cfc1d:/$ groups jenkins
jenkins : jenkins docker
What am I doing wrong? I want to use docker-commands with my jenkins user. I'm on Amazon EC2 Container Service.
This is how I start a container from my image:
docker run -d -v /var/run/docker.sock:/var/run/docker.sock -v
/usr/bin/docker:/usr/bin/docker:ro -v
/lib64/libdevmapper.so.1.02:/usr/lib/x86_64-linux-gnu/libdevmapper.so.1.02
-v /lib64/libudev.so.0:/usr/lib/x86_64-linux-gnu/libudev.so.0
-p 8080:8080 --name jenkins -u jenkins --privileged=true -t -i
my-jenkins:1.0

Answer 1

This was my 'solution' but it only worked on Ubuntu (not on my centos).
Dockerfile
FROM jenkins:1.651.1
USER root
RUN apt-get update \
&& apt-get install -y apt-transport-https ca-certificates \
&& echo "deb https://apt.dockerproject.org/repo debian-jessie main" > /etc/apt/sources.list.d/docker.list \
&& apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D \
&& apt-get update -y \
&& apt-get install -y docker-engine
RUN gpasswd -a jenkins docker
USER jenkins
Run command:
docker run -d -it -v /var/run/docker.sock:/var/run/docker.sock test-jenkins
On Ubuntu:
jenkins#c73c683b02d7:/$ whoami
jenkins
jenkins#c73c683b02d7:/$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c73c683b02d7 test-jenkins "/bin/tini -- /usr/lo" 2 minutes ago Up 2 minutes 8080/tcp, 50000/tcp
condescending_wing
It has something to do with gid I think:
cat /etc/group in container (on ubuntu and centos).
jenkins:x:1000:
docker:x:999:jenkins
cat /etc/group on Ubuntu (also 999)
docker:x:999:ubuntu
cat /etc/group on Centos (different gid)
docker:x:983:centos
There is probably a solution for this. But I only needed Ubuntu so did not go further in this.

Answer 2

Once your container is running, you can "patch" into the running container using different users using
docker exec -ti -u 0 jenkins bash // root
docker exec -ti -u 1 jenkins bash // probably jenkins
Using the root user, you can su jenkins if you need to switch to the jenkins user from the root user.
If you want to run docker containers inside your existing container (it seems like that is what you're trying), remember to start your docker container with the --privileged flag, eg docker run --privileged ...