install gitlab-ci-multi-runner in docker mode on ubuntu based machines. Docker needs to be installed beforehand

gl-ci.sh

#!/usr/bin/env bash
echo "check if gitlab-ci-multi-runner is installed..."
gitlab-ci-multi-runner &> /dev/null
if [ $? != 0 ]; then
  echo "NOT installed. Installing..."
  curl -L https://packages.gitlab.com/install/repositories/runner/gitlab-ci-multi-runner/script.deb.sh | sudo bash
  apt-get install gitlab-ci-multi-runner
else
  echo "IS installed. OK"
fi
echo "Removing broken runners if existent..."
gitlab-ci-multi-runner verify --delete
echo "OK"
echo "check if docker is running..."
docker info &> /dev/null
if [ $? != 0 ]; then
  echo "ERROR: docker info failed. Exitting"
  exit 1
else
  echo "OK"
fi
DETECTED_RUNNERS="$(expr $(gitlab-ci-multi-runner list 2>&1 | wc -l) - 1)"
echo "detected ${DETECTED_RUNNERS} runners..."
if [ $DETECTED_RUNNERS -lt 1 ]; then
  # exits with 1 if no runner is registered
  echo "No runner registered... Registering..."
  export REGISTRATION_TOKEN="PUT TOKEN HERE"
  export RUNNER_TAG_LIST="$(hostname -f),$(uname -m),$(arch),docker"
  export CI_SERVER_URL="https://my.git.lab/ci"
  export RUNNER_EXECUTOR="docker"
  export RUNNER_NAME="$(hostname -f)"
  if [ "$(arch)" = "armv7l" ]; then  
    export DOCKER_IMAGE=""
  elif [ "$(arch)" = "x86_64" ]; then
    export DOCKER_IMAGE="ubuntu"
  else
    echo "arch not supported"
        exit 1
  fi
  gitlab-ci-multi-runner register -n
fi