Re: Invoking user shepherd; Was: Re: Defining *user* services in Guix

[ludo@gnu.org (Ludovic Courtès)]

Hello!

Danny Milosavljevic <dannym@scratchpost.org> skribis:

> For a real user shepherd, it would be nice if when I logged in twice using the same user account (without logging out in-between - so resulting in two sessions of that user) it would still only have one shepherd instance for that user account in total - and if that instance (and remaining user processes for that matter) went away only when I logged out from *all* sessions of that user.
>
> I thought I could fake that by just trying to invoke shepherd on each session start and have it fail on the second attempt - but apparently we will happily start an infinite number of shepherds for one user.  Is that on purpose?
>
> The relevant place (in shepherd) is:
>
> (define (open-server-socket file-name)
>   "Open a socket at FILE-NAME, and listen for connections there."
>   (with-fluids ((%default-port-encoding "UTF-8"))
>     (let ((sock    (socket PF_UNIX SOCK_STREAM 0))
>           (address (make-socket-address AF_UNIX file-name)))
>       (false-if-exception (delete-file file-name)) ;  <===== [dannym: WTF.  Would it be better to try to connect first?]
>       (bind sock address)
>       (listen sock 10)
>       sock)))
>
> Probably not good.

The ‘delete-file’ was to avoid EADDRINUSE but I wonder if it’s really a
good idea.

> Maybe better:
>
> (define (server-present? file-name)
>   "Open a socket at FILE-NAME, and connect to the server, if any.  Return #t if that worked."
>   (with-fluids ((%default-port-encoding "UTF-8"))
>     (let ((sock    (socket PF_UNIX SOCK_STREAM 0))
>           (address (make-socket-address AF_UNIX file-name)))
>       (false-if-exception (connect sock address))))) ; probably missing a "[catch] close".  How to do that best?

That’s a pretty good test.  Note that (gnu services herd) and (shepherd
comm) already provide an ‘open-connection’ procedure to do that.

From a shell script, you can also simply run “herd status root” and
check the exit status.

> I'm trying to find the right place to insert my "dbus-daemon" invocation for providing the user bus (note: not session bus)...

What’s the difference between a “user bus” and a “session bus”?  In
general, my understanding is that the user dbus-daemon (session bus?) is
started on demand.

> Should we make a system shepherd service that invokes the user shepherd service on behalf of users?  Would that be that safe?

The “guix user” approach that Mathieu shown is more flexible than having
to do something in the ‘operating-system’ declaration IMO.

> Or should we just expect the user to put a (shepherd with fix) invocation into their HOME startup scripts like .xinitrc ?  Note that if we did that there's some session-specific stuff in the session's environment that shepherd will inherit.  Probably not that bad if invoked early enough.

Currently that’s what I do: my ~/.xinitrc runs shepherd and that’s it.

HTH,
Ludo’.