Ugh, that’s such a frustrating issue—especially when you’ve already checked the obvious cache suspects and resorted to renaming files just to make progress. Let’s dig into some less obvious culprits that might be causing your old functions.php files to stay stuck in a cached state, along with actionable fixes:

1. Overlooked OPcache Persistence #

Even if you think you cleared PHP’s internal cache, OPcache (PHP’s built-in bytecode cache) might still be holding onto the compiled version of your old functions.php. OPcache caches scripts to improve performance, but sometimes file modification timestamps don’t trigger a refresh correctly.

• Check if OPcache is enabled: Create a phpinfo.php file with <?php phpinfo(); ?> and look for the OPcache section.
• Fixes:
  • Restart your PHP service (PHP-FPM, Apache, or Nginx) to clear OPcache entirely.
  • Temporarily add opcache_reset(); right after your include line (only for debugging—remove this in production).
  • Adjust OPcache settings in php.ini:

    opcache.validate_timestamps = 1
    opcache.revalidate_freq = 1
    

    This forces OPcache to check for file updates every second during development.

2. Relative Path Ambiguity #

Your include('functions.php') uses a relative path, which might be pulling a different functions.php file depending on which script is including your layout file. For example, if your layout is included in a script in /admin/ vs /public/, PHP will look for functions.php in those directories instead of the one you’re editing.

• Fix: Use an absolute path to ensure you’re always loading the correct file:

  include(__DIR__ . '/functions.php');
  

  __DIR__ refers to the directory of the current layout file, so this guarantees you’re including the file in the same folder.

3. Hidden Server-Level Caching #

Some hosting providers use additional caching layers beyond PHP, like:

• Nginx fastcgi_cache
• Varnish
• Filesystem caching (common in cloud hosting environments)
• CDNs (though rare for dynamic PHP files)

These caches might serve the old functions.php even after you’ve updated it.

• Fixes:
  • Check your hosting control panel for a "Clear Cache" button (many hosts have this for server-level caches).
  • Contact your hosting provider to ask if they have any persistent caches that need invalidation.

4. Accidental Duplicate functions.php Files #

There might be another functions.php somewhere in your project that’s being included instead of the one you’re updating. PHP’s include path prioritizes certain directories, so if a parent directory has a functions.php, it might load that first.

• Verify which file is being loaded: Add this line right after your include to see all included files:

  var_dump(get_included_files());
  

  Look for the full path of functions.php in the output—this will tell you if it’s the file you’re editing or a duplicate elsewhere.

5. Silent File Upload Failures #

Even though renaming to functions4.php works, uploading to the old functions.php might be silently failing due to:

• Read-only file permissions

• File locks on the server

• FTP client transfer errors

• Fix:

  • Download the old functions.php from the server and check if your example() function is present. If not, the upload didn’t work.
  • Adjust file permissions to 644 (standard for PHP files).
  • Use SSH to overwrite the file directly (if you have access):

    cat /path/to/your/local/functions.php > /path/to/server/functions.php
    

6. Shared Hosting Bytecode Cache Limitations #

In shared hosting environments, OPcache might be shared across multiple sites, and you might not have permission to reset it or adjust settings. In this case, making a tiny change to the file (like adding a comment or extra newline at the top) can trigger OPcache to recompile the script, since it detects a change in file content.

内容的提问来源于stack exchange，提问作者Smashzap