Why is mod_perl producing the following errors in my apache web server 
log?

"null: Attempt to free unreferenced scalar."
"[notice] child pid 11830 exit signal Segmentation fault (11)"

It happens repeatedly and without pattern.

Hi,

I noticed that you already posted your question on several message boards.

The answer to your question depends on a number of factors, including the 
versions of Perl and mod_perl you are using, the Perl modules referenced by the 
scripts that cause the errors, whether you're using embedded Perl, etc. 

The most recommended solution is installing the latest versions of Perl and 
mod_perl that probably have the patches for these often discussed problems. 

Other solutions include not using certain Perl modules, such as 
Apache::StatINC, changing certain Apache directives, such as PerlFreshRestart, 
etc.

For many specific solutions that may work for your particular configuration,
have a look at the unreferenced scalar threads on the GeoCrawler mod_perl board:
http://www.geocrawler.com/search/?config=182&words=unreferenced+scalar

and the segmentation fault threads on Mathforum's mod_perl mailing list archive:
http://mathforum.org/epigone/modperl/jimpgingshu

Also, do report your problem to the mod_perl developers. Stas Bekman, one of 
the most active developers, already recommended that you do that in his reply 
at:

http://groups.yahoo.com/group/modperl/message/43498

and provided a link to the document on reporting mod_perl problems:
http://perl.apache.org/preview/modperl-
docs/dst_html/docs/1.0/guide/help.html#How_to_Report_Problems

More useful links:

Perldiag: Perl diagnostics (section on the unreferenced scalar error)
http://www.perldoc.com/perl5.6.1/pod/perldiag.html

Debugging mod_perl
http://perl.apache.org/guide/debug.html

mod_perl Guide (sections on errors and warnings)
http://perl.apache.org/guide/

mod_perl FAQ (section on errors)
http://perl.apache.org/faq/

Doug Sparling's mod_perl links collection
http://www.dougsparling.com/comp/links/modperl/

Useful Google searches:

"attempt to free unreferenced scalar" mod_perl OR modperl
"segmentation fault" OR segfault OR segfaults OR segv "exit signal" mod_perl OR 
modperl

Try to get some more info, and narrow down the problem. It would be useful if
you could know which script is causing the error. Try increasing the log level
to "debug". See here:
 http://httpd.apache.org/docs/mod/core.html#loglevel

Also look on access.log for pages with HTTP result codes other than 200. 

A word of advice, though: do this at non-peak usage times. Debug log level
writes lots of data to the disk and really slows down apache. If you have enough
RAM, mount a ramdisk and direct the error log there. ~256Mb should be enough if
error conditions are relatively frequent.