Date: Wed, 2 Jun 2004 11:11:49 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: Bruce Evans <bde@zeta.org.au> Cc: Mark Murray <mark@grondar.org> Subject: Re: Problems with periodic scripts in jails [Cron <operator@sosai> /usr/libexec/save-entropy] Message-ID: <20040602161148.GA3067@dan.emsphone.com> In-Reply-To: <20040603011806.E25331@gamplex.bde.org> References: <20040602134523.GA26835@genius.tao.org.uk> <20040602140148.GA27036@genius.tao.org.uk> <20040602140923.GA27070@genius.tao.org.uk> <20040603011806.E25331@gamplex.bde.org>
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In the last episode (Jun 03), Bruce Evans said: > On Wed, 2 Jun 2004, Josef Karthauser wrote: > > Ok, I've found the cause of the problem. Cron is spawning more > > than one copy of the entropy script... > > Cron has been filling my mailbox with complaints about this for > years. (I only partially filled the mailbox of the author of the > entropy script with complaints about it 3 or 4 times :-). In my > case, the multiple crons are caused by /usr being nfs-mounted and the > server being down. cron forks OK, but each copy blocks waiting for > something in /usr. When the server comes back up, a thundering herd > of entropy scripts run and clobber each others' rotation of the > entropy files. Cron normally runs the entropy script every 11 > minutes, so the herd grows quickly. The herd (or perhaps other > herds) also exhausts pipe kva on machines with small amounts of RAM > (64M) while waiting. A nice addition to cron might be a way to tell it that certain jobs should be single-instance. I know about half of my cron jobs look like: /usr/local/bin/lockfile -r 1 -l 3600 /tmp/runjob.LCK && ( runjob ; rm /tmp/runjob.LCK ) and it'd be handy if cron would do this internally (no physical lockfiles needed). The least intrusive way would be to add a magic variable similar to MAILTO; NO_OVERLAP=1 or something. Anyone up for a Junior Userland Hacker project? :) -- Dan Nelson dnelson@allantgroup.com
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