actions-runner-controller/runner/rootless-startup.sh

#!/bin/bash
source logger.bash

log.notice "Writing out Docker config file"
/bin/bash <<SCRIPT
mkdir -p /home/runner/.config/docker/

if [ ! -f /home/runner/.config/docker/daemon.json ]; then
  echo "{}" > /home/runner/.config/docker/daemon.json
fi

if [ -n "${MTU}" ]; then
jq ".\"mtu\" = ${MTU}" /home/runner/.config/docker/daemon.json > /tmp/.daemon.json && mv /tmp/.daemon.json /home/runner/.config/docker/daemon.json
# See https://docs.docker.com/engine/security/rootless/ and https://github.com/docker/engine/blob/8955d8da8951695a98eb7e15bead19d402c6eb27/contrib/dockerd-rootless.sh#L13
echo "DOCKERD_ROOTLESS_ROOTLESSKIT_MTU=${MTU}" >> /etc/environment
fi

if [ -n "${DOCKER_REGISTRY_MIRROR}" ]; then
jq ".\"registry-mirrors\"[0] = \"${DOCKER_REGISTRY_MIRROR}\"" /home/runner/.config/docker/daemon.json > /tmp/.daemon.json && mv /tmp/.daemon.json /home/runner/.config/docker/daemon.json
fi
SCRIPT

log.notice "Starting Docker (rootless)"
/home/runner/bin/dockerd-rootless.sh --config-file /home/runner/.config/docker/daemon.json >> /dev/null 2>&1 &

# Wait processes to be running
entrypoint.sh