Re: s6/s6-rc policy for Gentoo

Jan Braun <[email protected]> Mon, 8 Jul 2024 12:48:37 +0200
Newsgroups	gmane.comp.sysutils.supervision.general
Message-ID	<ZovEBTkjn2G_H0sC@abakus>
Paul Sopka schrob:
> An alternative would be two main bundles per user service tree, that itself
> always starts on boot:
> 
> One to start at boot time.
> Another one to start on first login and stop on last login.
> This seems the most elegant and efficient. Am I overlooking anything?

I am not too familiar with s6 bundles (I use runit, not s6), but that
sounds reasonable.

> > This sounds unnecessarily complicated. Why not simply test for existence
> > of a well-known entry point somewhere in $HOME and let that set up the
> > user supervision tree however it sees fit (or not at all)?
> 
> If I understand correctly, this would only be possible using instantiated
> services, I like the idea and I am looking into this.

Not sure what you mean by "instantiated services". But see below.

> > Ugh. I hate this thinking. [...]
> 
> It looks like I just do not have enough experience, that's why I am asking
> you all on those points. You are right.

Sorry for my tone, I realize I was grumpy, possibly offensively so. You
took it well, thanks. :)

> Using the idea I stated above, one could use different PAM modules to start
> different bundles tho, e.g. an ssh bundle on ssh login, a getty bundle on
> getty login, a greetd bundle on greetd login.

While I don't know why one would want to differentiate between those,
you probably can do that quite straightforwardly with pam_exec(8)
calling a tiny script that tracks the number of active sessions (of type
"$1") and calls s6-rc on zeroes.


And if you want to make this machinery user-customizable, you'll need
three user entry points:
~/.foo/supervisor
    defaulting to "s6-svscan $scandir"
~/.foo/login <type> <concurrent>
    defaulting to "if $concurrent == 0 then s6-rc start $type"
~/.foo/logout <type> <concurrent>
    defaulting to "if $concurrent == 0 then s6-rc stop $type"

And you'll need one admin action which creates the service supervising
~$USER/.foo/supervisor (if that service doesn't exist yet). To be
triggered on user account creation, or probably on login if things like
ldap are involved.

regards,
    Jan
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