How Do I Debug 'notice child pid XXXX exit signal Segmentation fault (11)' in Apache Error Logs?

Troubleshooting "notice child pid XXXX exit signal Segmentation fault (11)" in Apache Error Logs

When using the Apache/PHP/MySQL stack with the CakePHP framework, occasional blank white pages may occur without clear debug information within Cake. By examining Apache error logs, we frequently encounter entries such as:

[notice] child pid 3580 exit signal Segmentation fault (11)

This error indicates a segmentation fault, which is a type of run-time error that occurs when a program attempts to access memory that it is not authorized to access.

Debugging Using GDB

To pinpoint the source of the segmentation fault, we can attach the GNU Debugger (GDB) to one of the Apache child processes. Here's a step-by-step guide:

1. List the running Apache child processes using the command: ps -ef | grep httpd
2. Identify the PID of a problematic child process.
3. Attach GDB to the child process using: sudo gdb followed by attach [PID].
4. Restart or continue the server and wait for the crash.
5. Once the crash occurs, run the backtrace or backtrace full command in GDB to view the stack trace. This will provide valuable information about the origin of the error.

Optimizing Apache Configuration

If the segmentation fault is difficult to reproduce, consider modifying Apache's configuration to limit the use of child processes for handling requests. Add the following lines to your configuration file, such as /etc/apache2/httpd.conf:

StartServers 1
MinSpareServers 1
MaxSpareServers 1

This configuration ensures that only a single child process is used, making it easier to debug errors.

Additional Troubleshooting

Ensure that the following are up-to-date:

• PHP version (5.3.4 or higher recommended)
• Apache version (2.2.17 or higher recommended)
• CakePHP version (1.3.10 or higher recommended)

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