From owner-freebsd-questions  Tue Nov  9  8:11:55 1999
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From: vladimir@math.uic.edu
To: freebsd-questions@FreeBSD.ORG, grog@lemis.com,
	vladimir-freebsd-questions@math.uic.edu
Subject: Re: ktrace'ing a running process
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	>From grog@mojave.sitaranetworks.com Tue Nov 09 16:00:15 1999
	>Delivered-To: vladimir-freebsd-questions@math.uic.edu
	>Date: Tue, 9 Nov 1999 10:59:34 -0500
	>From: Greg Lehey <grog@mojave.sitaranetworks.com>
	>To: vladimir-freebsd-questions@math.uic.edu, freebsd-questions@FreeBSD.ORG
	>Subject: Re: ktrace'ing a running process
	>Mime-Version: 1.0
	>
	>On Tuesday,  9 November 1999 at 15:53:00 -0000, vladimir-freebsd-questions@math.uic.edu wrote:
	>> I ran into a problem:  ktrace -p PID produces
	>> a 0 length file ktrace.out, and ktrace exits
	>> immediately.   The system is FBSD-3.3-STABLE.
	>> What am I doing wrong?
	>
	>Not much.  You're probably just assuming that it's a bug for ktrace to
	>exit immediately, and in fact it's a feature.  To stop the trace,
	>enter 'ktrace -p PID -C'.
	>
	>The real question is: why is your process not producing any ktrace
	>output?  It may not be running, or it may be looping in user space.
	>Remember that ktrace shows only the transitions between user and
	>kernel space.  If you don't have any such transitions, you won't get
	>any output.
	>
	>What does 'ps lp PID' say?
	>
	>Greg

Ah, you are right.  I wrote a c program that does stat on a file in a loop;
this one produced the output.  I assumed ktrace should just wait 
until it detects interaction with the kernel, but it looks like it 
just exits.
Thanks!
	Vladimir


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