Re: Apache2 prefork children dying with WebGUI/modperl 1.99_11

[Stas Bekman]

Jay R. Ashworth wrote:
On Thu, Nov 27, 2003 at 05:12:10PM -0800, Stas Bekman wrote:

httpd -DONE_PROCESS -DNO_DETACH


Oh, *ick*; it's a Heisenbug.

This time it didn't dump core -- it did what it was doing originally:
In which case you can run the server normally and still get the core file, but 
in addition to the ulimit command you need to make the directory where httpd 
resides writable by the user the server is running under. The whole path to 
that directory needs to +x to that user.

The easiest way for you to test whether you can get the core dumped is this. 
let's say your httpd resides in /appl/Apache/bin/httpd, so we do:

% su
% cd /appl/Apache/bin/
% perl -MPOSIX -e 'my($uid, $gid) = (getpwnam(shift))[2..3]; \
    POSIX::setuid($uid); POSIX::setgid($gid); \
    print -r q{$dir} &&  -w _ && -x _ ? q{OK} : q{NOK};' \
  nobody
If you get NOK that means that the core file won't be dumped. If OK, then 
it'll work. In fact you can just try to dump the core as that user in a 
similar way:

% su
% cd /appl/Apache/bin/
% perl -MPOSIX -e 'my($uid, $gid) = (getpwnam(shift))[2..3]; \
    POSIX::setuid($uid); POSIX::setgid($gid); \
    CORE::dump;' \
  nobody
If you get:

Abort

That means that the core wasn't dumped. If you get:

Abort (core dumped)

then you will find a "nice" core file in /appl/Apache/bin/

So let's say you don't get the core, what you do next is fixing the perms of 
the whole path leading to the location of httpd:

% su
% cd /appl/Apache/bin/
% perl -e 'use File::Spec::Functions qw(splitdir); use Cwd; \
       my($uid, $gid) = (getpwnam(shift))[2..3]; \
       @dirs = splitdir(Cwd::cwd); shift @dirs; \
       chown $uid, $gid, "." and chdir ".." for @dirs' \
  nobody
(The above could be written in a simpler way, assuming that we are on Unix, 
but it's been a while since I stopped assuming things about platforms and try 
to write a portable code from the very beginning)

Now try to get the core file again. Remember that you just adjusted the whole 
path to be owned by that user ('nobody') in our example. You may want to go 
and restore the original ownership after you are done with the core.

Notice that all these scripts are run as root, and we assume that the server 
is running under the user nobody.

Again, notice that the core file could be something like core.16291, where the 
number after . is the pid of the process that dumped that core.

__________________________________________________________________
Stas Bekman            JAm_pH ------> Just Another mod_perl Hacker
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