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Date:      Mon, 12 Sep 2022 09:16:44 +0200 (CEST)
From:      freebsd@oldach.net (Helge Oldach)
To:        cy@FreeBSD.org (Cy Schubert)
Cc:        src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org
Subject:   Re: git: 3418c14040f2 - stable/13 - libexec/rc: Add var_run rc script
Message-ID:  <202209120716.28C7Gjd2091559@nuc.oldach.net>
In-Reply-To: <202209120041.28C0fEHa096990@gitrepo.freebsd.org> from Cy Schubert at "12 Sep 2022 00:41:14"

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Cy Schubert wrote on Mon, 12 Sep 2022 02:41:14 +0200 (CEST):
>     libexec/rc: Add var_run rc script
>     
>     Users with a tmpfs /var/run will lose the directory tree state of
>     /var/run at reboot. This rc script will optionally (by default)
>     capture the state of the directory structure in /var/run prior to
>     shutdown and recreate it at system boot.
>     
>     Alternatively a user can save the state of the /var/run directories
>     manually using service var_run save and disable the autosaving of
>     /var/run state using the var_run_autosave variable, for those
>     paranoid SSD users.

I'm afraid this logic does not rhyme well with a common scenario: Firing
up a tmpfs based /var by simply booting with a non-writeable /var which
will trigger /etc/rc.d/var to create, mount and populate a tmpfs based
/var. This is the classic diskless scenario.

The concern is that var_run by default saves the var_run created mtree
on exactly this tmpfs based /var (as /var/db/mtree/BSD.var-run.mtree) so
it will be gone with the next reboot. This will void the var_run logic
for the default case.

I would suggest to document that tweaking var_run_mtree appropriately is
necessary for such scenarios.

Furthermore, I propose to consider extending the scope of var_run from
/var/run to the whole of /var, which would be sensible in certain
diskless cases as well.

Kind regards
Helge



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