rancherOS/docs/os/system-services/built-in-system-services/index.md

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title: Built-in System Services in RancherOS

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Built-in System Services

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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.

In start up order, here are the groups of services:

1. Device and power management:
2. udev-cold
3. udev

4. acpid

5. syslog

6. System configuration and networking:

7. preload-system-images

8. cloud-init-pre

9. network-pre

10. ntp

11. cloud-init

12. network

13. User interaction:

14. console

15. docker

16. Post configuration:

17. preload-user-images

preload-system-images & preload-user-images

Read more about pre-packing Docker images.

cloud-init-pre

User-data (i.e. cloud-config) and metadata from cloud provider, VM runtime, or a management service, is loaded in this service.

The user-data is written to:

• /var/lib/rancher/conf/cloud-config.d/boot.yml - If the user-data is a cloud-config, i.e. begins with #cloud-config and is YAML format.
• /var/lib/rancher/conf/cloud-config-script - If the user-data is a script, i.e begins with #!.
• /var/lib/rancher/conf/metadata - If it is serialized cloud provider metadata.

It is configured by the rancher.cloud_init.datasources list in cloud-config. It is pre-configured in cloud-provider specific images (e.g. AWS, GCE).

network-pre

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.

cloud-init

It does the same thing as cloud-init-pre, but in this step, it can also use the network to fetch user-data and metadata (e.g. in cloud providers).

network

Completes setting up networking with configuration obtained by cloud-init.

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).

RancherOS Configuration Load Order

Cloud-config is read by system services when they need to get configuration. Each additional file overwrites and extends the previous configuration file.

1. /usr/share/ros/os-config.yml - This is the system default configuration, which should not be modified by users.
2. /usr/share/ros/oem/oem-config.yml - This will typically exist by OEM, which should not be modified by users.
3. Files in /var/lib/rancher/conf/cloud-config.d/ ordered by filename. If a file is passed in through user-data, it is written by cloud-init and saved as /var/lib/rancher/conf/cloud-config.d/boot.yml.
4. /var/lib/rancher/conf/cloud-config.yml - If you set anything with ros config set, the changes are saved in this file.
5. Kernel parameters with names starting with rancher.
6. /var/lib/rancher/conf/metadata - Metadata added by cloud-init.