Date: Sun, 23 Nov 2003 10:35:44 +0000 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: "Cordula's Web" <cpghost@cordula.ws> Cc: questions@freebsd.org Subject: Re: Monitoring a file? Message-ID: <20031123103544.GD9494@happy-idiot-talk.infracaninophile.co.uk> In-Reply-To: <200311231017.hANAHvpd097677@fw.farid-hajji.net> References: <200311222258.hAMMwApd092388@fw.farid-hajji.net> <16320.5175.69241.145102@jerusalem.litteratus.org> <200311231017.hANAHvpd097677@fw.farid-hajji.net>
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On Sun, Nov 23, 2003 at 11:17:57AM +0100, Cordula's Web wrote:
> > > A file, let's say, /path/to/a/file, is being modified by
> > > an unknown process P(u) at random times. Unfortunately,
> > > the name of the program ran by P(u) is unknown.
> >=20
> > Have you tried moving the file elsewhere and seeing if anyone
> > complains about the absence?
>=20
> No, P(u) obviously fails silently. There's nothing recorded
> by syslog, no messages on the console, and no core dumps...
>=20
> > Or writing a program that locks the file?
>=20
> That was a good idea. However, P(u) didn't seem to take a lock.
> Advisory locks are just that: if P(u) doesn't lock the file,
> existing locks don't matter at all. Do we have mandatory locks
> in FreeBSD?
Not a lock as such, but:
# chflags schg /path/to/a/file
should achieve the effect you desire. Although this will cause any
write on the file to just fail, rather than causing P(u) to block
waiting for a lock. You could try replacing /path/to/a/file with a
fifo (see mkfifo(1)), and maybe hang another process on the other end
of the fifo which can run ps(1) or fstat(1) when a write is detected.
Cheers,
Matthew
--=20
Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks
Savill Way
PGP: http://www.infracaninophile.co.uk/pgpkey Marlow
Tel: +44 1628 476614 Bucks., SL7 1TH UK
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