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From "Gonyou, Austin" <aus...@coremetrics.com>
Subject RE: dumps on Linux: some progress
Date Thu, 09 Aug 2001 17:06:45 GMT
The answer to this lies in the fact that nobody owns nothing in /. / is
nobody's home dir in /etc/passwd. I can get nobody to dump core when running
top, if his homedir is someplace writeable. Alternately, I can get nobody to
dump core, even if his homedir is not writeable, but he owns the dir in
which he might dump core(working dir). 

To illustrate this point, I told /etc/passwd that nobody's homedir was /tmp,
su - nobody, top(then kill 11 on top's pid).
I get a core in Nobody's homedir.
If I reset nobody's home back to /, then su - nobody, cd /tmp, top(then kill
11 on top's pid), I still get a core. 
-- 
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-796-9023
email: austin@coremetrics.com 

> -----Original Message-----
> From: Gonyou, Austin [mailto:austin@coremetrics.com]
> Sent: Thursday, August 09, 2001 11:00 AM
> To: 'new-httpd@apache.org'
> Subject: RE: dumps on Linux: some progress
> 
> 
> Hmm..I'll research this a bit and see what I come up with. I 
> think I can
> find the answer here. 
> 
> -- 
> Austin Gonyou
> Systems Architect, CCNA
> Coremetrics, Inc.
> Phone: 512-796-9023
> email: austin@coremetrics.com 
> 
> > -----Original Message-----
> > From: Greg Ames [mailto:gregames@remulak.net]
> > Sent: Thursday, August 09, 2001 10:10 AM
> > To: new-httpd@apache.org
> > Subject: dumps on Linux: some progress
> > 
> > 
> > Last nite I figured out how to get a core dump of a 
> threaded server on
> > Linux when it seg faults.  After Justin pointed out that he's 
> > seen dumps
> > w/threaded, I noticed that I had a few old dumps in my home 
> directory,
> > and one in root's home directory, but nothing my configured
> > CoreDumpDirectory (writeable by everybody w/the sticky bit set).
> > 
> > I had "User nobody" and "Group nobody" in my config file, to match
> > daedalus as closely as possible.  hmmmm..."nobody" doesn't 
> have a home
> > directory.  So I created "webuser" which does have a home 
> > directory, and
> > only belongs to its own group.  Changed the config file to use this
> > user/group, fired up threaded with mod_cgid, did an 
> > "apachectl restart",
> > and voila! a coredump appeared in my CoreDumpDirectory.  
> > 
> > I still don't know exactly what the deal is here (i.e., is it 
> > important
> > that "webuser" has a home dir?  is Mandrake's security 
> stuff or Linux
> > itself doing something to "nobody"? does this have anything 
> to do with
> > using threads?) but thought it might be useful to other folks.
> > 
> > Still nothing in the error log.  This shouldn't be a surprise 
> > - we don't
> > have code that logs when the parent itself seg faults.
> > 
> > Thanks to Justin for letting us know that core dumps are possible
> > w/threaded on Linux, and to Ben whose Horse book is where I 
> > got the idea
> > for "webuser".
> > 
> > Greg
> > 
> 

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