$ packer build -var github_feed_token=XXXX images/linux/ubuntu1804.json
docker: output will be in this color.
==> docker: Creating a temporary directory for sharing data...
==> docker: Pulling Docker image: buildpack-deps:18.04
docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.40/images/create?fromImage=buildpack-deps&tag=18.04: dial unix /var/run/docker.sock: connect: permission denied
==> docker: Error pulling Docker image: Bad exit status: 1
Build 'docker' errored after 71 milliseconds 304 microseconds: Error pulling Docker image: Bad exit status: 1
==> Wait completed after 71 milliseconds 340 microseconds
==> Some builds didn't complete successfully and had errors:
--> docker: Error pulling Docker image: Bad exit status: 1
==> Builds finished but no artifacts were created.