bug#53580: /var/run/shepherd/socket is missing on an otherwise functional system

[Ludovic Courtès]

Hello Attila,

I had totally overlooked this bug report.

Attila Lendvai <attila@lendvai.name> skribis:

> the systems seems to work fine. Gnome is up, i can log in with my user, and 
> everything seems to work, except herd.
>
> i encounter this broken state every once in a while. IRC logs also mention 
> this multiple times, but without many insights:
>
> https://logs.guix.gnu.org/guix/search?query=%2Fvar%2Frun%2Fshepherd%2Fsocket
>
> ```
> # herd status
> error: connect: /var/run/shepherd/socket: No such file or directory

[...]

> the issue is that when Shepherd is booting up, i.e. starting from its config 
> file, it calls the start forms without guarding for any possible exceptions. 
> any error propagates up beyond the loop and up until an unwind protect that 
> deletes the socket.
>
> the reason my system seemed fully functional is that my service was pretty 
> much the last one to be started.

Currently (in 0.10.0), the ‘run-daemon’ procedure loads the user’s
config file before listening on /var/run/shepherd/socket.  However, if
an exception is thrown from the config file, it stops:

--8<---------------cut here---------------start------------->8---
$ echo '(error "oops")' > /tmp/conf.scm
$ ./shepherd -I -s sock -c /tmp/conf.scm
Starting service root...
Service root started.
Service root running with value #t.
Service root has been started.
misc-error(#f "~A" ("oops") #f)

Some deprecated features have been used.  Set the environment
variable GUILE_WARN_DEPRECATED to "detailed" and rerun the
program to get more information.  Set it to "no" to suppress
this message.
$ echo $?
1
--8<---------------cut here---------------end--------------->8---

Now, while the config file is being evaluated, shepherd does not listen
on its socket, which isn’t great.

This is mitigated by the use of ‘start-in-the-background’ (introduced in
0.9.0) in the config file, which, as the name implies, doesn’t block
further operation.

So I *think* we’re mostly okay now.  The one thing we could do is load
the whole config file in a separate fiber, and maybe it’s fine to keep
going even when there’s an error during config file evaluation?

WDYT?

Thanks,
Ludo’.