Getting permission denied with docker pipeline on jenkins

Question

I have jenkins deployed via helm charts on kubernetes cluster Now i want to be able to run helm to deploy helm charts applications on my kubernetes cluster and have the following in my jenkinsfile

pipeline {
    agent {
        docker { image 'alpine/helm' }
    }
    stages {
        stage('Deploy') {
            steps {
                sh 'helm ls'
            }
        }
    }
}

I also get kubernetes authentication setup on my jenkins so connection to cluster is fine but the error am getting now is the following

+ docker inspect -f . alpine/helm

Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.38/containers/alpine/helm/json: dial unix /var/run/docker.sock: connect: permission denied
[Pipeline] isUnix
[Pipeline] sh
+ docker pull alpine/helm
Using default tag: latest
Warning: failed to get default registry endpoint from daemon (Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.38/info: dial unix /var/run/docker.sock: connect: permission denied). Using system default: https://index.docker.io/v1/
Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.38/images/create?fromImage=alpine%2Fhelm&tag=latest: dial unix /var/run/docker.sock: connect: permission denied
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
ERROR: script returned exit code 1
Finished: FAILURE

What am i missing and how to i get out of this error?

Thanks

UPDATE

below are the additions/changes to default values.yaml file of the stable/jenkins helm chart

agent:
  enabled: true
  image: "joao29a/jnlp-slave-alpine-docker"
  tag: "latest"
  customJenkinsLabels: []
  # name of the secret to be used for image pulling
  imagePullSecretName:
  componentName: "jenkins-slave"
  #privileged: false
  privileged: true

  resources:
    requests:
      cpu: "512m"
      memory: "512Mi"
    limits:
      cpu: "512m"
      memory: "512Mi"
  # You may want to change this to true while testing a new image
  alwaysPullImage: false
  # Controls how agent pods are retained after the Jenkins build completes
  # Possible values: Always, Never, OnFailure
  podRetention: "Never"
  # You can define the volumes that you want to mount for this container
  # Allowed types are: ConfigMap, EmptyDir, HostPath, Nfs, Pod, Secret
  # Configure the attributes as they appear in the corresponding Java class for that type
  # https://github.com/jenkinsci/kubernetes-plugin/tree/master/src/main/java/org/csanchez/jenkins/plugins/kubernetes/volumes
  # Pod-wide ennvironment, these vars are visible to any container in the agent pod
  envVars: []
  # - name: PATH
  #   value: /usr/local/bin
  volumes:
  # - type: Secret
  #   secretName: mysecret
  #   mountPath: /var/myapp/mysecret
   - type: HostPath
     hostpath: /var/run/docker.sock
     mountPath: /var/run/docker.sock

everything else pretty much same except for ingress hostnames and admin user password...above is most important modification to default values.yaml file

Answer 1

You need to add the jenkins user to the docker group:

# run the following command as root
usermod -aG docker jenkins