using fabric8 docker-maven-plugin in a Jenkins docker container
In above mention sequence first you started Jenkins and then you have added jenkins user in docker group. if this is the case, changes is not reflected for the Jenkins server. but when you are executing manually, at that time jenkins added to docker group. To test - create a test job and execute script "id -a". this will show groups for user Jenkins at that point of time. same cmd execute from inside of container. if there is difference, i would suggest you to create a dockerfile with all above installation and useradd and then start Jenkins.