Built-in System Services

To launch RancherOS, we have built-in system services. They are defined in the Docker Compose format, and can be found in the default system config file, /usr/share/ros/os-config.yml. You can add your own system services or override services in the cloud-config.

preload-user-images

Read more about image preloading.

network

During this service, networking is set up, e.g. hostname, interfaces, and DNS.

It is configured by hostname and rancher.networksettings in cloud-config.

ntp

Runs ntpd in a System Docker container.

console

This service provides the RancherOS user interface by running sshd and getty. It completes the RancherOS configuration on start up:

  1. If the rancher.password=<password> kernel parameter exists, it sets <password> as the password for the rancher user.

  2. If there are no host SSH keys, it generates host SSH keys and saves them under rancher.ssh.keys in cloud-config.

  3. Runs cloud-init -execute, which does the following:

    • Updates .ssh/authorized_keys in /home/rancher and /home/docker from cloud-config and metadata.
    • Writes files specified by the write_files cloud-config setting.
    • Resizes the device specified by the rancher.resize_device cloud-config setting.
    • Mount devices specified in the mounts cloud-config setting.
    • Set sysctl parameters specified in therancher.sysctl cloud-config setting.

  4. If user-data contained a file that started with #!, then a file would be saved at /var/lib/rancher/conf/cloud-config-script during cloud-init and then executed. Any errors are ignored.

  5. Runs /opt/rancher/bin/start.sh if it exists and is executable. Any errors are ignored.

  6. Runs /etc/rc.local if it exists and is executable. Any errors are ignored.

docker

This system service runs the user docker daemon. Normally it runs inside the console system container by running docker-init script which, in turn, looks for docker binaries in /opt/bin, /usr/local/bin and /usr/bin, adds the first found directory with docker binaries to PATH and runs dockerlaunch docker daemon appending the passed arguments.

Docker daemon args are read from rancher.docker.args cloud-config property (followed by rancher.docker.extra_args).