How do I stop/debug/trace segmentation faults? (Moved from Q&A)

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I have a script that collects SNMP information on a bunch of routers that continues to seg fault on me about 10-25 % of the time.

It creates an array of Net::SNMP objects and then steps through that array, querying each router for certain information and then writing it all out to an RRD file.

I have it doing some minor logging, but since it runs on a crontab I've never actually seen it seg fault. I believe it's doing it during the gather phase, but I'm not sure.

My longwinded question is, is there any way I can track down what's causing this or at least where it's happening ? I've tried to throw some eval statements, but that doesn't stop the segmentation fault

BTW, I'm running it on a FreeBSD 3.4 box with 512Mb of RAM. The box is rather busy, so could it be a lack of memory issue ?

Any help at all would be greatly appreciated.

Comment on How do I stop/debug/trace segmentation faults? (Moved from Q&A)

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Re: How do I stop/debug/trace segmentation faults? (Moved from Q&A) by rlk (Pilgrim) on Dec 07, 2000 at 22:21 UTC
Hmm, this is just off the top of my head, but how about replacing the line in your crontab with one that does `yes "s" \| perl -d (your script here) > logfile` [download] -- Ryan Koppenhaver, Aspiring Perl Hacker "I ask for so little. Just fear me, love me, do as I say and I will be your slave."	[reply] [d/l]
Re: Re: How do I stop/debug/trace segmentation faults? (Moved from Q&A) by BlueLines (Hermit) on Dec 08, 2000 at 05:17 UTC
Actually, you wouldn't want to do that, as the logfile would be written over every time the cronjob ran. You'd probably want to do something liike this: `date >> logfile && perl -d (your script here) 2>&1 >> logfile` The >> will append to the logfile rather than overwrite it, and the `2>&1` redirects `stderr` to `stdout`, assuming you are running bash. I'm not sure of the syntax for tcsh/ksh/csh/etc, but i'm pretty sure that there will be more useful debugging info in `stderr` than in `stdout`. BlueLines Disclaimer: This post may contain inaccurate information, be habit forming, cause atomic warfare between peaceful countries, speed up male pattern baldness, interfere with your cable reception, exile you from certain third world countries, ruin your marriage, and generally spoil your day. No batteries included, no strings attached, your mileage may vary.	[reply] [d/l] [select]
Re: Re: Re: How do I stop/debug/trace segmentation faults? (Moved from Q&A) by rlk (Pilgrim) on Dec 08, 2000 at 07:29 UTC
i'm pretty sure that there will be more useful debugging info in stderr than in stdout While your suggestion of duping stderr to stdout is a good one, my chief concern was capturing the output of the debugger, sent to stdout, the last line of which would be the line which caused the segfault. -- Ryan Koppenhaver, Aspiring Perl Hacker "I ask for so little. Just fear me, love me, do as I say and I will be your slave."	[reply]
Re: How do I stop/debug/trace segmentation faults? (Moved from Q&A) by Russ (Deacon) on Dec 07, 2000 at 22:20 UTC
chewlies posted here as I was moving his post from Categorized Questions and Answers. May I suggest to the learned monks to post thy replies to Segmentation Faults 10-20% of the time? Russ Brainbench 'Most Valuable Professional' for Perl	[reply]
Re: How do I stop/debug/trace segmentation faults? (Moved from Q&A) by whiteEFunk (Acolyte) on Feb 24, 2005 at 08:41 UTC
check out valgrind. I used this to trace a number of segfaults within my Inline::C code. http://valgrind.kde.org	[reply]
Sieve Method by DentArthurDent (Monk) on Aug 29, 2003 at 12:37 UTC
I've never had a perl script dump, but in C the best way is often to pepper the code with logging statements and see which is the last one to come out. Just make sure that all of the statements will get printed directly and not buffered or you'll confuse yourself! Hope that helps!	[reply]


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