Re: Improving Shepherd

[ludo@gnu.org (Ludovic Courtès)]

Hey!

Danny Milosavljevic <dannym@scratchpost.org> skribis:

> On Mon, 05 Feb 2018 21:49:08 +1100
> Carlo Zancanaro <carlo@zancanaro.id.au> wrote:
>
>> User services - Alex has already sent a patch to the list to allow 
>> generating user services from the Guix side. The idea is to 
>> generate a Shepherd config file, allowing a user to invoke 
>> shepherd manually to start their services.
>
>>A further extension to 
>> this would be to have something like systemd's "user sessions", 
>> where the pid 1 Shepherd automatically starts a user's services 
>> when they log in.
>
> I assume that means "starts a user's shepherd when they log in".
>
> elogind already emits a signal on dbus which tells you when a user logged in
>
>         return sd_bus_emit_signal(
>                         u->manager->bus,
>                         "/org/freedesktop/login1",
>                         "org.freedesktop.login1.Manager",
>                         new_user ? "UserNew" : "UserRemoved",
>                         "uo", (uint32_t) u->uid, p);

I think there’s Guile D-Bus client though.  Another yak to shave…

> Also, a directory /run/user/<id> appears - which alternatively can be
> monitored by inotify or something.
>
> So the system shepherd could have a shepherd service which does
>
>   while (1) {
>      wait until /run/user/<id> appears
>      vfork
>        if child: setuid, exec user shepherd, _exit
>        if parent: wait until child dies
>   }
>
> We better be sure that no one else can create directories in /run/user .
>
> In non-pseudocode, both "wait until /run/user/<id> appears" and
> "wait until child dies" would have to be in the same call,
> maybe epoll or something.

Yes, inotify (ISTR there *are* inotify bindings for Guile somewhere.)

> Maybe call the service shepherd-nursery-service or something, like a star
> nursery :)

:-)

Ludo’.