Troubleshooting PHP

Overview

PHP can fail for a variety of reasons. This is a growing list of reasons for which a PHP script may fail or behave inconsistently:

Output

Empty pages

Compiler error

By default, PHP will not display compile-time errors or any notice/error message. These are instead logged to improve security against malicious hackers. You can change this through a .htaccess directive: php_flag display_errors on located within the document root.

To resolve: Depending upon the nature, there are a few solutions:

• Syntax error: correct the syntax mistake, use a suitable IDE to edit PHP files to avoid typos like PDT (free) or PhpStorm (mixed cost)
• Miscellaneous compiler errors: ensure the PHP script has been uploaded properly to the FTP server. Sometimes, a bad FTP client will inappropriately try to resume a text file resulting in code spliced into itself by file offsets
  • Open a ticket in the control panel and we’ll direct you on this! happens more often than you’d expect

Bad cache retrieval

PHP utilizes an intermediate cache that takes compiled bytecode and saves it in memory to avoid  compilation every time a page is requested. In certain circumstances, bytecode compilation gets jumbled resulting in an empty page.

To resolve: Disable PHP caching. Depending on platform version, the following directive should be added to a .htaccess file within the document root of the affected web site:

• v6 and newer platforms, which use OPcache:
  php_flag opcache.enable off
• v5 and older platforms, which use APC:
  php_flag apc.cache_by_default off

Interaction

Undefined behavior

Behavior that exists beyond the expectations (ie. upload file stores a file) can result from deprecation or outright disuse of old constructs, like register_globals.

To resolve: purely situational, but there is an order of resolution:

1. Ensure that you are operating the latest version of the application
2. Look for errors in the web server log files
   • Open a ticket for assistance for any issues present
3. Add php_flag display_errors on and php_value error_reporting 99999 to a .htaccess file in the document root of the application. Try to reproduce the issues looking for any additional output prefixed with “PHP Error” or “PHP Notice”
   • Can’t resolve the issue based upon error/warning/notice context? Open a ticket and let us know how to reproduce it
4. In certain cases, there can be intricate complications between PHP, software, and even microcode
   • Open a ticket with steps to reproduce the issue, and we’ll look into it
     • In the past, issues have ranged from unexpected Zend Engine interaction to CPU abnormalities