http://stackoverflow.com/questions/36614105/access-docker-within-container-on-jenkins-slave

Jenkins dockerized slave accessing docker

FROM centos:7
MAINTAINER Georg Heiler <georg.heiler@convista.com>

# Install Essentials
RUN yum update -y && \
    yum clean all

# Install Packages
RUN yum install -y git && \
    yum install -y wget && \
    yum install -y which && \
	yum install -y openssh-server && \
	yum install -y java-1.8.0-openjdk && \
	yum install -y java-1.8.0-openjdk-devel && \
	yum install -y sudo && \
	yum clean all

# gen dummy keys, centos doesn't autogen them like ubuntu does
RUN /usr/bin/ssh-keygen -A

# Set SSH Configuration to allow remote logins without /proc write access
RUN sed -ri 's/^session\s+required\s+pam_loginuid.so$/session optional pam_loginuid.so/' /etc/pam.d/sshd

# Create Jenkins User
RUN useradd jenkins -m -s /bin/bash

# Add public key for Jenkins login
RUN mkdir /home/jenkins/.ssh

COPY /files/authorized_keys /home/jenkins/.ssh/authorized_keys

RUN chown -R jenkins /home/jenkins
RUN chgrp -R jenkins /home/jenkins
RUN chmod 600 /home/jenkins/.ssh/authorized_keys
RUN chmod 700 /home/jenkins/.ssh

# Add the jenkins user to sudoers
RUN echo "jenkins    ALL=(ALL)    ALL" >> etc/sudoers

# Set Name Servers
COPY /files/resolv.conf /etc/resolv.conf

# Set docker sock volumes needed for linux host as the compose-yml file is not used by jenkins to start a job
VOLUME /var/run/docker.sock
VOLUME /var/lib/docker

ENV JAVA_HOME=/usr/lib/jvm/jre
# Expose SSH port and run SSHD
EXPOSE 22
CMD ["/usr/sbin/sshd","-D"]