Re: How to declare symlinks in the configuration?

[Gary Johnson <lambdatronic@disroot.org>]

Marek Paśnikowski <marekpasnikowski@protonmail.com> writes:

> Thank you Gary.
>
> This is the kind of answer I was hoping for. Could you also share with
> me the corresponding service-type for the system configuration?

Hi Marek,

  In the system configuration, most of the files that you would edit by
hand on another distro (e.g., config files under /etc) are not managed
directly by a single service in Guix System. Instead, you typically add
services (e.g., `postgresql-service-type`, `cups-service-type`,
`strongswan-service-type`) to your `operating-system` definition and
declare their configurations within each service's scheme code.

For example, here is how you might edit the config files for a
Postgresql server:

```scheme
(use-modules
 ((gnu packages databases) #:select (postgresql))
 ((gnu packages geo)       #:select (postgis))
 ((gnu services)           #:select (service))
 ((gnu services databases) #:select (postgresql-service-type postgresql-configuration postgresql-config-file))
 ((gnu services desktop)   #:select (%desktop-services))
 ((gnu system)             #:select (operating-system))
 ((guix gexp)              #:select (local-file)))

(operating-system
 ;; ...Eliding all the fields except `services`...
 (services (cons (service postgresql-service-type
                          (postgresql-configuration
                           (postgresql postgresql)
                           (extension-packages (list postgis))
                           (config-file
                            (postgresql-config-file
                             (hba-file (local-file "etcfiles/pg_hba.conf"))
                             (extra-config '(("max_worker_processes" "12")
                                             ("max_parallel_workers" "40")
                                             ("max_parallel_maintenance_workers" "8")
                                             ("max_parallel_workers_per_gather" "4")
                                             ("parallel_leader_participation"
                                             "on")))))))
                 %desktop-services)))
```

In this example, I showed two ways of specifying the contents of a
config file for this service:

1. Using `local-file` to pull in the contents of a text file somewhere
   on disk. In this case, I keep my system-wide service config files
   under a directory called "etcfiles" (in my home directory). For
   config files referenced in my `guix home` configuration, I use a
   directory called "dotfiles".

2. Including the contents of these files directly in the
   `operating-system` declaration. In this case, you see me specifying
   key-value pairs for the main Postgresql config file in a nested list
   under the `extra-config` record parameter.

=======================================================================

Now...having provided the above explanation as the typical usage pattern
for configuring services on Guix System, I will add that there is an
escape hatch that you can use (as a last resort if there isn't an
existing service that controls the files you want to edit).

This is the service called `etc-service-type`. You can use it to declare
any arbitrary files that would like added immutably under the top level
"/etc" directory. You can use it like so:

```scheme
(use-modules
 ((gnu services)           #:select (service etc-service-type))
 ((gnu services desktop)   #:select (%desktop-services))
 ((gnu system)             #:select (operating-system))
 ((guix gexp)              #:select (local-file)))

(operating-system
 ;; ...Eliding all the fields except `services`...
 (services (cons (service etc-service-type
                          `(("resolv.conf" ,(local-file "etcfiles/resolv.conf"))))
                 %desktop-services)))
```

Now you know, and knowing is half the battle. ;)
Have fun and happy hacking on Guix!

  ~Gary

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