forked from dan/liminix
doc: how to define an s6 service
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@ -84,3 +84,52 @@ domains, or you want to run two SSH daemons on different ports.
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combining configuration values from different sources. We
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don't use the NixOS modules themselves, because the
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underlying system is not similar enough for them to work.
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Services
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********
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We use the s6/s6-rc system to start/stop/restart services and handle
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service dependencies. Any attribute in `config.services` will become
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part of the default set of services that s6 will try to bring up on
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boot.
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For the most part, for common use cases, hopefully the services you
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need will be defined by modules and you will only have to pass the
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right parameters to ``build``.
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Should you need to create a custom service of your own devising, use
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the `oneshot` or `longrun` functions:
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* a "longrun" service is the "normal" service concept: it has a
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``run`` action which describes the process to start, and it watches
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that process to restart it if it exits. The process should not
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attempt to daemonize or "background" itself, otherwise s6 will think
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it died. . Whatever it prints to standard output/standard error
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will be logged.
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.. code-block:: nix
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config.services.cowsayd = pkgs.liminix.services.longrun {
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name = "cowsayd";
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run = "${pkgs.cowsayd}/bin/cowsayd --port 3001 --breed hereford";
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}
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* a "oneshot" service doesn't have a process attached. It consists of
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``up`` and ``down`` actions which are bits of shell script that
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are run at the appropriate points in the service lifecycle
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.. code-block:: nix
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config.services.greenled = pkgs.liminix.services.oneshot {
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name = "greenled";
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up = ''
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echo 17 > /sys/class/gpio/export
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echo out > /sys/class/gpio/gpio17/direction
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echo 0 > /sys/class/gpio/gpio17/value
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'';
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down = ''
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echo 0 > /sys/class/gpio/gpio17/value
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'';
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}
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