RC API

The rc system automates running scripts as services and is generally used for starting scripts when the system is booting up. It is one tool of many provided by OpenOS for automatic script execution, as documented here.

OpenOS rc is inspired by OpenRC. “rc” stands for “run command”.

There are two components of the rc system; rc scripts and the rc controller.

RC Scripts

RC scripts are lua modules built by the user and managed by the rc controller. We will cover how to build your own rc script. “Enabled” rc scripts are those configured to start at boot. The rc controller can also start and stop an rc script individually, without having to enable or disable it.

RC scripts are lua scripts that require minimal setup, their method api is flexible, and can also benefit from an rc configuration.

Minimal Setup

To create a custom rc script named “custom” you minimally need one file /etc/rc.d/custom.lua with minimally one function defition

snippet.lua
function start()
end

This one custom.lua file with its one start function sufficiently defines an rc script.

The astute reader will have noticed that our start function in the minimal example is lacking a local scope designation. This was intentional. RC scripts are loaded in a sandboxed environment and these global functions act as an interface between the source and the rc controller. Every method you want the rc controller to have access to needs to be a globally defined method in your rc script file.

OpenOS ships is an example rc script. Review /etc/rc.d/example.lua

RC Script Methods

To the casual reader the details of the rc script environment may only seem a distraction to getting started with the rc system. But, for the curious or the confused, these details can be helpful. The RC script is loaded (lua load) in a sandboxed environment inheriting all global methods to OpenOS. Your global functions in the rc script are accessible to the rc system and do not pollute the OpenOS global environment. Your script configuration is in your sandbox environment as a global variable args. Also note that your script is loaded once and kept in cache.

The rc script name is the basename of the lua file you've added to /etc/rc.d/.

Define your rc script methods as global functions in your rc script file. Note that in no case does the rc system care about the return value of any rc script method. Data of any exception throw will be printed to stderr if available, otherwise to /tmp/event.log.

There are only 2 rc methods that hold a special status in the rc system, start and stop.

  • start()

A proper rc script needs only to define a start method. The design of the rc system anticipates that rc scripts can be started, and through various workflows with the controller, the system levarages the start method.

  • stop()

Optionally, the rc script may define a stop method. Enabled rc scripts (i.e. scripts that are configured for automatic startup) will only call start during boot, but rc <custom> restart also has a default behavior if a stop method has been defined for a script. When the rc controller is asked to restart any rc script it will call stop followed by start. Note that if the script has defined restart explicitly, that is called instead.

  • <methodName>([args...])

The rc script author is not limited to defining only start and stop. You have the flexibility to define any number of script methods. The end user will not call these methods directly, but will instead leverage the rc controller to call these methods. Thus there is a common calling convention the rc controller uses to call any named rc script method.

# rc <moduleName> <methodName> [args...]

Where moduleName is your rc script name (that being the basename of your .lua file located in /etc/rc.d/), methodName is your global method defined in that script file, and args... are any command line arguments you want to pass. Even start and stop can be called this way.

RC Script Configuration

You can define your own script configuration in /etc/rc.cfg (the syntax of this file must be lua-readable). If your rc script is at /etc/rc.d/foo.lua, then its module name is foo, and its configuration field name would be foo. The example rc script, provided with OpenOS, does this. It has a /etc/rc.d/example.lua script, and the /etc/rc.cfg has:

snippet.lua
example = "Hello World"
enabled = {}

The enabled table it maintained by the controller, but the example field holds the configuration for the example rc script. The value of the field can be any lua value, not just a string, and that includes tables. The configured value for your script is loaded into your script environment. You can access your configuration in your script via a global field named args. Again, review the example.lua script code at note its use of an args variable. Your script file and the configuration loaded once and cached by the controller.

The RC Controller

The rc controller has a command line interface you access with the rc command in the shell (/bin/rc.lua) and a library you can access via require("rc"). It maintains a list of which rc scripts are configured to start at boot, and keeps a cache of the loaded rc scripts. Unlike the other automatic start options autorun and .shrc, enabled rc scripts only automatically start once per OpenOS boot.

Command Line Interface

rc

Calls start on all enabled rc scripts

rc <moduleName> enable

Adds rc script <moduleName> to the list of “autostarting” rc scripts. Next boot, <moduleName>.start() will be called.

rc <moduleName> disable

Removes rc script <moduleName> from the enabled list. Next boot, <moduleName> will not be started.

rc <moduleName> restart

If rc script <moduleName> has a stop() and start() method defined, call them.

rc <moduleName> <methodName> [args...]

Call the function <method> defined in rc script <moduleName>, passing [args…] (if any) to it as function arguments.

RC API

  • unload(moduleName: string)

You can unload your rc script thereby removing it from the rc cache. This would be necessary if you want to reconsume your configuration, or clear any script globals. It can definitely be helpful when debuging and you want to reload your script code without having to reboot the system.

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