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From Tomasz Chmielewski <man...@wpkg.org>
Subject Re: [users@httpd] debugging websites running on Apache?
Date Fri, 19 Nov 2010 14:01:36 GMT
On 19.11.2010 14:39, Igor Galić wrote:

>> What are other debugging methods which can be used on a busy
>> webserver?
>> Ideally, I'd like to see all connections, database queries, files
>> opened
>> for read/write by Apache processes, with timestamps, as I connect from
>> a
>> given IP address (so all other noise is excluded).
>
> Even with strace you can reduce the amount of syscalls you see.
> Check strace(1) for the -e option.

> If you're on a modern Operating System, you'll have something like
> DTrace or SystemTap in place, which is a big plus, as it ads almost
> no overhead to your actions, and could be considered monitoring.

It's not the amount of syscalls printed by strace which is a problem, 
but those caused not by me (i.e. by some other user from a different IP 
browsing the website).

I don't really see how dtrace or systemtap can help here.

In the end, Xdebug doesn't seem to be it for my usage case (at least, 
not everywhere, or it wouldn't give all hints I should have).

For example, I don't see how it could tell that the webserver did:

execve("/bin/sh", ["sh", "-c", "/usr/sbin/sendmail -t -i"],

which later failed with:

open("maildrop/77441.19034", O_RDWR|O_CREAT|O_EXCL, 0644) = -1 EACCES 
(Permission denied)

Which made the webserver loop and retry due to some bad code in an 
obfuscated PHP product.


Oh well. Having a few webservers in the balancer and using one just for 
yourself is a nice thing to have, but I guess I won't always have it 
available.

On the other hand, if there is just one webserver, most likely it's not 
that important, and can take some downtime for debugging.


-- 
Tomasz Chmielewski
http://wpkg.org

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