Date: Mon, 11 Dec 2000 00:43:34 +0000 From: Brian Somers <brian@Awfulhak.org> To: Robert Watson <rwatson@FreeBSD.org> Cc: Brian Somers <brian@Awfulhak.org>, Dag-Erling Smorgrav <des@ofug.org>, "David E. O'Brien" <obrien@FreeBSD.org>, cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org, brian@Awfulhak.org Subject: Re: cvs commit: src/etc crontab Message-ID: <200012110043.eBB0hYV06366@hak.lan.Awfulhak.org> In-Reply-To: Message from Robert Watson <rwatson@FreeBSD.org> of "Sat, 09 Dec 2000 22:42:41 EST." <Pine.NEB.3.96L.1001209223834.82272B-100000@fledge.watson.org>
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>
> On Sat, 9 Dec 2000, Brian Somers wrote:
>
> > It makes things a bit un-orthogonal though. Maybe something like
> > this would be more appropriate:
> >
> > 1 3 * * * root lockf /var/run/periodic periodic daily
> > 1 3 * * 6 root lockf /var/run/periodic periodic weekly
> > 1 3 1 * * root lockf /var/run/periodic periodic monthly
>
> While this is really much cleaner and appealing to me, it runs into the
> usual file locking problem: since they're advisory, they're inter-user and
> enforced for root (!). As such, any random process running as any random
> user can acquire the lock and stack up all your periodic scripts, DoSing
> you. And it's hard to track down, too, since it's hard to figure out what
> processes own what locks. This actually applies to a really large number
> of other related problems: for example, when locking is used to protect
> mailboxes, any user can deny service by acquiring locks on all mailboxes,
> etc. Usually the solution is to only use locks on objects which are
> appropriately protected, unfortunately.
I chose /var/run because it's only writable by root.
> On a related note, this is also more susceptible to cascading failure, as
> it queues the work rather than canceling it if resources aren't available.
This is no worse than what's already there though. I guess it would
make sense to have a job run at 5:00 that checks the lock and moans
if it still exists.... but I think that's a bit horrible.
> Robert N M Watson FreeBSD Core Team, TrustedBSD Project
> robert@fledge.watson.org NAI Labs, Safeport Network Services
--
Brian <brian@Awfulhak.org> <brian@[uk.]FreeBSD.org>
<http://www.Awfulhak.org>; <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !
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