Hello ndeloof

You tell about --volume-from, you mean docker run --volumes-form $BUILD_CONTAINER_ID?

juliengarcia This means that if you launch the Jenkins docker container with a docker --volume parameter that shares the host system's /var/jenkins_home and /tmp directories, then this plug-in can work when being used by Jenkins that is, itself, a container.

Here is a snippet of the docker run cmd line I use: docker run -v /var/jenkins_home:/var/jenkins_home -v /tmp:/tmp -p 8080:8080 -p 50000:50000 -d jenkins

As I may have more than one jenkins master running on one docker host, I cannot add -v /var/jenkins_home:/var/jenkins_home at run time. So, I've solved this by creating a symlink in the Jenkins container from /var/jenkins_home to the same foldername as my mount point on the host to /var/jenkins_home and told the Jenkins master that $JENKINS_HOME is equal to this symlink.
So (no ports exposed as I access jenkins via an apache container in the same network):

docker run -v /var/run/docker.sock:/var/run/docker.sock -v /bin/docker:/bin/docker \
   -v /usr/lib64/libdevmapper.so.1.02:/usr/lib/libdevmapper.so.1.01 \
   -v /data/jenkins_01/home:/var/jenkins_home -v /tmp:/tmp --env JENKINS_HOME=/data/jenkins_01/home \
   --name jenkins_01 -d myjenkins

Last line of my Dockerfile:

ENTRYPOINT /usr/local/bin/prepare_jenkins.sh \
  && HOME=$JENKINS_HOME gosu jenkins /bin/tini -- /usr/local/bin/jenkins.sh

prepare_jenkins.sh:

if [[ "${JENKINS_HOME}" !=  "/var/jenkins_home" ]]; then
   mkdir -p $(dirname ${JENKINS_HOME})
   ln -sf -T /var/jenkins_home ${JENKINS_HOME}
fi
grep docker /etc/group || groupadd -g $(stat -c "%g" /var/run/docker.sock) docker
usermod -a -G docker jenkins

I just submitted a pull-request that addresses this issue. Comments appreciated!

https://github.com/jenkinsci/docker-custom-build-environment-plugin/pull/38

I should also mention that accessing the Docker socket from within the Jenkins container not possible by default if the Jenkins process runs as a non-root user (which will be the case when running the official JenkinsCI container). This Stack Overflow answer covers how to open socket permissions up in this scenario:

http://stackoverflow.com/a/33183227

I run jenkins container as user jenkins, but before running jenkins in a 'prepare_jenkins.sh' step, I add jenkins user to the docker group, which is added if it does not exist already. See above code fragment. It works. No need to chmod a+s of /usr/bin/docker or sudo.

tallandtree, that worked great, thanks for that! I'm using the official JenkinsCI container, which already has a group (users) with the same id (100) as the group which owns `docker.sock` on my docker host, so I tweaked your groupadd line to add the `-o` option, which permits the additon of a group with a non-unique GID.

grep docker /etc/group || groupadd -g $(stat -c "%g" /var/run/docker.sock) -o docker

I'm running docker in a container and I get this error on every jenkins (docker) slave I try to run on:

Error response from daemon: Cannot start container 3fc0dc09: [8] System error: no such file or directory
22:04:54 FATAL: Failed to run docker image
22:04:54 java.lang.RuntimeException: Failed to run docker image
22:04:54 	at com.cloudbees.jenkins.plugins.docker_build_env.Docker.runDetached(Docker.java:226)
22:04:54 	at com.cloudbees.jenkins.plugins.docker_build_env.DockerBuildWrapper.startBuildContainer(DockerBuildWrapper.java:202)
22:04:54 	at com.cloudbees.jenkins.plugins.docker_build_env.DockerBuildWrapper.setUp(DockerBuildWrapper.java:175)
22:04:54 	at hudson.model.Build$BuildExecution.doRun(Build.java:156)
22:04:54 	at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:534)
22:04:54 	at hudson.model.Run.execute(Run.java:1738)
22:04:54 	at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
22:04:54 	at hudson.model.ResourceController.execute(ResourceController.java:98)
22:04:54 	at hudson.model.Executor.run(Executor.java:410)
22:04:54 Finished: FAILURE

Including here to help other find this when internet searching.