To setup gitlab-ci-multi-runner follow the Installation using GitLab’s repository for Debian/Ubuntu/CentOS/RedHat (preferred) as described on gitlab website.

Install curl

~$ apt-get update; apt-get install curl;

To use Docker runner, install it before using the multi runner:

~$ curl -sSL https://get.docker.com/ | sh

Add GitLab’s official repository via apt-get or yum:

# For Debian/Ubuntu
~$ curl -L https://packages.gitlab.com/install/repositories/runner/gitlab-ci-multi-runner/script.deb.sh | sudo bash

Install gitlab-ci-multi-runner:

# For Debian/Ubuntu
~$ sudo apt-get install gitlab-ci-multi-runner

Find your project page

https://gitlab.com/dashboard/projects

Enter the project page and choose Settings at the lower left corner, scroll down to Advanced settings and copy CI token

https://gitlab.com/mygroup/my-project/edit

Register the runner.

~$ sudo gitlab-ci-multi-runner register

        Please enter the gitlab-ci coordinator URL (e.g. https://gitlab.com/ci )
        https://gitlab.com/ci
        Please enter the gitlab-ci token for this runner
        xxx
        Please enter the gitlab-ci description for this runner
        my-runner
        INFO[0034] fcf5c619 Registering runner... succeeded
        Please enter the executor: shell, docker, docker-ssh, ssh?
        docker
        Please enter the Docker image (eg. ruby:2.1):
        ruby:*
        INFO[0037] Runner registered successfully. Feel free to start it, but if it's
        running already the config should be automatically reloaded!


~# cat /etc/gitlab-runner/config.toml 

concurrent = 5

[[runners]]
  name = "docker-runner"
  url = "https://gitlab.com/ci"
  token = "xx"
  tls-ca-file = ""
  executor = "docker"
  [runners.docker]
    image = "debian:jessie"
    privileged = false
    volumes = ["/cache"]
    allowed_images = ["ruby:*", "python:*", "java:*", "gcc:*"]


~# gitlab-runner status

    gitlab-runner: Service is running!

Finaly go to GitLab dashboard and check the new runner :-)

https://gitlab.com/admin/runners