Re: Staging Scheme code to run as one-shot service

[Owen T. Heisler]

On 3/4/24 21:07, Owen T. Heisler wrote:
> On 3/4/24 10:08, Felix Lechner wrote:
>> try something like this:
>>
>>      (start #~(let ((port (open-pipe* OPEN_WRITE "logger" 
>> "-plocal0.alert")))
>>                 (display "========say-hello========\n" port)
>>                 (close-pipe port)))
> 
>> [1] 
>> https://codeberg.org/lechner/juix/src/commit/fe8cac5165bfbe290413cedd36a492109e29e38b/juix/deploy/cachefilesd.scm#L158
> 
> Thanks for the suggestion. I tried that, but it doesn't work either.

Apparently I failed to follow your example properly and had an extra 
`#~(begin` in there. I have a minimal example now that does work, 
including with the G-expression defined separately.

As I wrote in another message, I also got a boot script 
(non-Shepherd) service working (with the help of a hint from Florian) 
but I need to use a regular Shepherd service so I can declare a 
dependency on another service (in this case, syslogd).

Here is the working example:

```scm
;; $(guix system vm input.scm --no-graphic)
(use-modules (gnu)
             (gnu services shepherd)
             (ice-9 popen))
(use-service-modules networking)
(use-package-modules admin bootloaders)
(define say-hello-gexp
  #~(begin
      (let ((port (open-pipe* OPEN_WRITE
                              #$(file-append inetutils "/bin/logger")
                              "-plocal0.alert"))
            ;; Use random string to counter syslog deduplication
            (rand_str (number->string (random 100))))
        (display (string-append "====say-hello" rand_str "====\n") port)
        (close-pipe port))))
(define say-hello-service
  (simple-service 'say-hello-service shepherd-root-service-type
                  (list (shepherd-service (auto-start? #t)
                                          (documentation "Say hello.")
                                          (one-shot? #t)
                                          (provision '(say-hello-service))
                                          (requirement '(syslogd))
                                          (respawn? #f)
                                          (start #~(lambda _
                                                     #$say-hello-gexp))))))
(operating-system
  (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
                (targets '("/dev/vda"))
                (terminal-inputs '(console serial))
                (terminal-outputs '(console serial))
                (timeout 1)))
  (file-systems (cons (file-system
                        (mount-point "/")
                        (device "/dev/vda1")
                        (type "ext4")) %base-file-systems))
  (host-name "test-guix-vm")
  (kernel-arguments (cons "console=ttyS0" %default-kernel-arguments))
  (services
   (append (list say-hello-service) %base-services)))
;; # herd start say-hello-service
```

Thanks,
Owen