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I'm working on Centos7. I have a Docker container which is running Jenkins. In that Jenkins-container I have to build and run other Docker containers. But Jenkins doesn't know docker. I'm able to execute a shell and install docker inside the container. But isn't it possible to let the container use my docker-engine on the host? How can I use it?

What is the best option to install Docker inside a Jenkins-(docker)-container?

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Generally, a container-in-container setup involves linking /var/run/docker.sock and docker itself.
For example, in this thread:

docker run --name jenkins --privileged=true -t -i --rm -v /var/run/docker.sock:/var/run/docker.sock -v $(which docker):/bin/docker -p 8080:8080 jenkins

This is not exactly your case, since you don't need to run Jenkins itself in a "cic" (container in container").
But that illustrates how you would run any container in a container, with docker available in it.

Make sure the user in that container is part of the docker group (if you don't want to use root), as in this jenkins/setup-docker-and-start-jenkins.sh script

#!/bin/sh set -e JUSER="jenkins" DOCKER_GID=$(ls -aln /var/run/docker.sock | awk '{print $4}') if ! getent group $DOCKER_GID; then echo creating docker group $DOCKER_GID addgroup --gid $DOCKER_GID docker fi if ! getent group $GID; then echo creating $JUSER group $GID addgroup --gid $GID $JUSER fi if ! getent passwd $JUSER; then echo useradd -N --gid $GID -u $UID $JUSER useradd -N --gid $GID -u $UID $JUSER fi DOCKER_GROUP=$(ls -al /var/run/docker.sock | awk '{print $4}') if ! id -nG "$JUSER" | grep -qw "$DOCKER_GROUP"; then adduser $JUSER $DOCKER_GROUP fi chown -R $JUSER:$JUSER /var/jenkins_home/

Note that this setup uses tini to launch Jenkins (as I described in "Jenkins does not run automatically after install in Docker container")

exec su $JUSER -c "/bin/tini -- /usr/local/bin/jenkins.sh"

Again, those scripts are for using Jenkins in "cic".
In your case, you can use those scripts for the containers that your Jenkins will have to run.

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Using the official Jenkins docker image: 

docker run -d \ -u root \ -v /var/run/docker.sock:/var/run/docker.sock \ -v $(which docker):/usr/bin/docker:ro \ -p 8080:8080 \ --name jenkins \ jenkins

Then to verify everything is working:

  • create a new job
  • add a shell script as a build step with docker version as content

If you run into the following error on CentOS 7:

docker: error while loading shared libraries: libsystemd-journal.so.0: cannot open shared object file: No such file or directory

then start the container with:

docker run -d \ -u root \ -v /var/run/docker.sock:/var/run/docker.sock \ -v $(which docker):/usr/bin/docker:ro \ -v /usr/lib64/libsystemd-journal.so.0:/usr/lib/x86_64-linux-gnu/libsystemd-journal.so.0 \ -v /usr/lib64/libsystemd-id128.so.0:/usr/lib/x86_64-linux-gnu/libsystemd-id128.so.0 \ -v /usr/lib64/libdevmapper.so.1.02:/usr/lib/x86_64-linux-gnu/libdevmapper.so.1.02 \ -v /usr/lib64/libgcrypt.so.11:/usr/lib/x86_64-linux-gnu/libgcrypt.so.11 \ -v /usr/lib64/libdw.so.1:/usr/lib/x86_64-linux-gnu/libdw.so.1 \ -p 8080:8080 \ --name jenkins \ jenkins
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Executing a docker command gave me: docker: error while loading shared libraries: libsystemd-journal.so.0: cannot open shared object file: No such file or directory
@Jenson I was able to figure this out, answer updated for CentOS 7 specificities.
Thanks, also correct. Only it seems not that good to use root and not the jenkinsuser to talk with docker, isn't it?
it all depends if you want to expose this Jenkins on the Internet or if you control the network on which it will be deployed. Otherwise, remove -u root but then in your Jenkins jobs, use sudo docker version instead of just calling docker version. See github.com/thomasleveil/… for differents ways to share docker from a host to a container
But I would refrain myself from exposing any docker container on the Internet if that container shares the /var/run/docker.sock socket with the docker host.
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