Add Shepherd service to GuixSD

This post must be same tutorial for GuixSD as https://nixos.org/wiki/NixOS:extend_NixOS for NixOS.

Lets create own guile modules structure:

$ mkdir local-guix
$ cd local-guix
$ mkdir -p mnd/services # we will use service modules like (use-modules (mnd services service))
$ edit irssi.scm # create irssi service

And create service that will run irssi under screen

Basic service

Firstly define module that will export our irssi-service

(define-module (mnd services irssi)
  #:use-module (gnu services)
  #:use-module (gnu services shepherd)
  #:use-module (gnu packages irc) ; irssi
  #:use-module (gnu packages screen)
  #:use-module (guix gexp)
  #:use-module (guix records)
  #:use-module (ice-9 match)
  #:export (irssi-service))

Then define config for our module

(define-record-type* <irssi-configuration>
  irssi-configuration make-irssi-configuration
  irssi-configuation?
  (irssi         irssi-configuration-irssi        ;<package>
                 (default irssi))
  (screen        irssi-configuration-screen       ;<package>
                 (default screen))
  (user          lirc-configuration-user)         ;string
  (group         lirc-configuration-group         ;string
                 (default "users"))
  (extra-options lirc-configuration-options       ;list of strings
                 (default '())))

Basicaly services extend activation-service-type and shepherd-root-service-type, but our service does not require to create runtime files so we’ll extend only shepherd-root-service-type:

(define irssi-shepherd-service
  (match-lambda
    (($ <irssi-configuration> irssi screen user group options)
        (list (shepherd-service
               (provision '(irssi))
               (documentation "Run the irssi client in screen.")
               (requirement '(user-processes))
               (start #~((make-forkexec-constructor
                          (list 
                           (string-append #$screen "/bin/screen")
                           "-D" "-m" "-S" "irc"
                           (string-append #$irssi "/bin/irssi")
                           #$@options))))
               (stop #~(make-kill-destructor)))))))

For now we ignore user and group options and just call irssi inside screen. This service will run irssi from root user.

Now we can define irssi-service-type that provides service with name irssi and extend shepherd-root-service-type with defined code.

(define irssi-service-type
  (service-type (name 'irssi)
                (extensions
                 (list (service-extension shepherd-root-service-type
                                          irssi-shepherd-service)))))

And finally define function that will create our <service> object:

(define* (irssi-service #:key (irssi irssi)
                        (screen screen)
                        user
                        (group "users")
                        (extra-options '()))
  "irssi service for specific user" 
  (service irssi-service-type
           (irssi-configuration
            (irssi irssi) (screen screen)
            (user user) (group group)
            (extra-options extra-options))))

Run this service

To add service to you system you must modify you system configuration file in next manner.

  1. Add (use-modules (mnd services irssi)) to beginning of the file
  2. Add (irssi-service #:user "alice") to list of services

And now you can add you new service to system with

$ su # log in as root
$ guix system -L /path/to/local-guix reconfigure /path/to/your-system-config.scm
...
making '/gnu/store/3j7wfbyhfs4pzrgdq6p8fnj4msyv01zc-system' the current system...
guix system: loading new services: irssi...
guix system: shepherd: Evaluating user expression (register-services (primitive-load "/gnu/s...")).
guix system: shepherd: Service irssi has been started.

Installation finished. No error reported.
$ herd status irssi
Status of irssi:
  It is started.
...

Add support for specific user

You can look at code that support specific user at github

Debugging

Guix and shepherd not very specific with errors. If something goes wrong you can try to load your module with guile:

$ guile -L /path/to/local-guix -L ${HOME}/.config/guix/latest/
scheme@(guile-user)> (use-modules (mnd services irssi))

TODO Some more usefull debug suggestions?

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