Debugging a hanging PHP script

September 11, 2015

I installed a script called test.php on a Vagrant box with CentOS 6.x and PHP 5.3. I made my script available at http://example.local/test.php and it contains:

<?php

function whatever() {
  sleep(1);
}

while (TRUE) {
  whatever();
}

When I access this page, it just loads forever, as would be expected.

Here is one way to debug this:

Start by downloading the Xdebug extension

cd
sudo pecl install xdebug-2.2.7

If you get “phpize not found”, then run:

yum install php-devel

and try installing again.

Figure out the path of your xdebug .so file, like this:

find / -name 'xdebug.so' 2>/dev/null

This will give something like this:

/usr/lib64/php/modules/xdebug.so

Now, figure out where your php.ini file is:

php --ini|grep Loaded

This will give you something like:

Loaded Configuration File:         /etc/php.ini

Add these lines to the end of that file:

zend_extension=/usr/lib64/php/modules/xdebug.so
xdebug.profiler_enable = 1;
xdebug.profiler_output_dir = "/tmp"

Now restart Apache:

sudo apachectl restart

Download Webgrind in the same directory as test.php.

git clone https://github.com/jokkedk/webgrind.git

Now visit http://example.local/test.php, and it will hang.

To figure out why it’s hanging, on another page go to http://example.local/webgrind, and click “Update” periodically. A list of costly functions (in this case whatever() and sleep()) will be shown.