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doc: how to define an s6 service

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Daniel Barlow 2023-09-17 00:30:49 +01:00
parent 54526c1e11
commit c74543c4ff
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@ -84,3 +84,52 @@ domains, or you want to run two SSH daemons on different ports.
combining configuration values from different sources. We
don't use the NixOS modules themselves, because the
underlying system is not similar enough for them to work.
Services
********
We use the s6/s6-rc system to start/stop/restart services and handle
service dependencies. Any attribute in `config.services` will become
part of the default set of services that s6 will try to bring up on
boot.
For the most part, for common use cases, hopefully the services you
need will be defined by modules and you will only have to pass the
right parameters to ``build``.
Should you need to create a custom service of your own devising, use
the `oneshot` or `longrun` functions:
* a "longrun" service is the "normal" service concept: it has a
``run`` action which describes the process to start, and it watches
that process to restart it if it exits. The process should not
attempt to daemonize or "background" itself, otherwise s6 will think
it died. . Whatever it prints to standard output/standard error
will be logged.
.. code-block:: nix
config.services.cowsayd = pkgs.liminix.services.longrun {
name = "cowsayd";
run = "${pkgs.cowsayd}/bin/cowsayd --port 3001 --breed hereford";
}
* a "oneshot" service doesn't have a process attached. It consists of
``up`` and ``down`` actions which are bits of shell script that
are run at the appropriate points in the service lifecycle
.. code-block:: nix
config.services.greenled = pkgs.liminix.services.oneshot {
name = "greenled";
up = ''
echo 17 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio17/direction
echo 0 > /sys/class/gpio/gpio17/value
'';
down = ''
echo 0 > /sys/class/gpio/gpio17/value
'';
}