Facing Drupal fatal error cannot redeclare format_size()? Learn how to remove duplicate modules, check code conflicts, and restore your site quickly. Our Drupal Support team is always here to help you.
Solving Drupal Fatal Error Cannot Redeclare format_size()
Seeing Drupal fatal error cannot redeclare format_size() can throw you off, especially when your website suddenly crashes without warning. This problem usually happens when the format_size() function is defined more than once in your Drupal setup. In most cases, it comes from having duplicate modules or conflicting code inside your installation.
Let’s go through everything that causes this and how you can solve it efficiently.
An Overview
Why This Error Appears
The Drupal fatal error cannot redeclare format_size() shows up when there are two or more copies of the same function, module, or file loaded by Drupal. The system doesn’t know which one to use, and the conflict breaks the site instantly.
A similar message might look like this:
Fatal error: Cannot redeclare system_requirements() (previously declared in /modules/system/system.install:12)
in /modules/modules/system/system.install on line 299When this happens, the solution isn’t complicated. You just need to find and remove the duplicates.
How to Resolve It
Start by checking for duplicate or conflicting code. Below are the essential areas to review:
1. Check for Duplicate Code
Go through your custom code, theme files, and contributed modules. See if format_size() is being defined more than once. Make sure no two files are declaring it simultaneously.
2. Review Contributed Modules
Verify you’re not including the same module multiple times. Sometimes developers accidentally keep two different versions of the same module in the modules or sites/all/modules/ directory. That’s what triggers the Drupal fatal error cannot redeclare format_size().
3. Scan for Duplicate Folders
Check your modules and sites/all/modules/ folders. Look carefully for repeated module directories. Once you find them, delete the duplicate folders.
4. Review Custom Code
If you have custom-written functions using format_size(), make sure you’re not redeclaring it by mistake. Also, check any included third-party files or libraries that could redefine the same function.
5. Inspect Theme Files
Sometimes theme files declare helper functions that overlap with module functions. Ensure your theme isn’t defining format_size() again.
6. Clear Your Drupal Cache
After removing duplicates or editing code, always clear the cache. Go to Configuration → Development → Performance, then click Clear all caches. Cached data can still load the old function and continue causing the same issue.
7. Recheck Module Order
Occasionally, the order in which modules are loaded may cause the error. Try changing the loading order and see if that resolves the issue.
8. Confirm File Naming
Make sure there aren’t two files with the same name that define the function. For example, both a theme and a module having a file named common.inc could cause confusion.
9. Update Old Modules
Outdated modules may also be responsible. Always keep your contributed modules up-to-date and compatible with your Drupal version.
10. Check Third-Party Libraries
If you’re using external libraries, inspect them for conflicts involving format_size().
11. Debug if Needed
If the issue persists, use debugging tools like debug_backtrace() to find where the duplicate declaration originates. Drupal’s built-in debugging can also help track the file and line number.
12. Inspect the Database
In rare cases, database inconsistencies might contribute to strange behavior. Make sure your database is healthy and not adding to the conflict.
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Conclusion
Before making any changes, always back up your site and database. Once you’ve cleaned up duplicates and cleared the cache, your Drupal site should run smoothly again.
The Drupal fatal error cannot redeclare format_size() may look intimidating, but the fix is usually straightforward, find the duplicates, remove them, and refresh. With a bit of careful inspection, your site will be back online without any lingering issues.
