Generating a Backtrace

If you don't have a core file yet

Read  generating a Backtrace on php.net.

• config xcache.coredump_directory in /etc/php.ini, For apache + mod_php, you have  CoreDumpDirectory in apache.conf
• Ensure that the xcache.coredump_directory has write permissions for the user who's running PHP
• Remove any limits you may have on core dump size from your shell:
  • tcsh: unlimit coredumpsize
  • bash/sh: ulimit -c unlimited
• Cause PHP to crash:
  • PHP CGI: Simply run php with the script that crashes it
  • PHP FastCGI: Simply setup normal webserver-fastcgi configuration, and access the script that crashes PHP
  • PHP As Apache Module: Run httpd -X, and access the script that crashes PHP

Once you have the core file

First, check where the coredump is

Checking where the coredump is

$ grep xcache.coredump_directory /etc/php.ini
xcache.coredump_directory = "/tmp/"
$ ls /tmp/core
/tmp/core

• PHP as CGI/FastCGI: Run gdb with the path to the PHP or PHP-enabled httpd binary, and path to the core file, for example:

Generating backtrace for PHP as CGI/FastCGI

$ gdb /usr/local/bin/php-cgi-fcgi /tmp/core
........
(gdb) bt
(gdb) source ~/src/php5/.gdbinit
(gdb) dump_bt executor_globals.current_execute_data

• PHP As Webserver Module: Run gdb with the path to the PHP or PHP-enabled httpd binary, and path to the core file, for example:

Generating backtrace for PHP as As Webserver Module

$ gdb /usr/local/apache/sbin/httpd /tmp/core
........
(gdb) bt
(gdb) source ~/src/php5/.gdbinit
(gdb) dump_bt executor_globals.current_execute_data