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.


Read more about image preloading.


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

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


Runs ntpd in a System Docker container.


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.


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).

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