Running Commands

You can automate running commands on boot using the runcmd cloud-config directive. Commands can be specified as either a list or a string. In the latter case, the command is executed with sh.

#cloud-config
runcmd:
- [ touch, /home/rancher/test1 ]
- echo "test" > /home/rancher/test2

Commands specified using runcmd will be executed within the context of the console container. More details on the ordering of commands run in the console container can be found here.

Running Docker commands

When using runcmd, RancherOS will wait for all commands to complete before starting Docker. As a result, any docker run command should not be placed under runcmd. Instead, the /etc/rc.local script can be used. RancherOS will not wait for commands in this script to complete, so you can use the wait-for-docker command to ensure that the Docker daemon is running before performing any docker run commands.

#cloud-config
rancher:
write_files:
  - path: /etc/rc.local
    permissions: "0755"
    owner: root
    content: |
      #!/bin/bash
      wait-for-docker
      docker run -d nginx

Running Docker commands in this manner is useful when pieces of the docker run command are dynamically generated. For services whose configuration is static, adding a system service is recommended.

Running Commands Early in the Boot Process

The bootcmd parameter can be used to run commands earlier in the boot process. In particular, bootcmd will be executed while RancherOS is still running from memory and before System Docker and any system services are started.

The syntax for bootcmd is the same as runcmd.

#cloud-config
bootcmd:
- [ mdadm, --assemble, --scan ]