Why does PHP throw a \'Call to undefined function json_decode()\' error, even with a version greater than 5.1?

"Call to Undefined Function json_decode()"

PHP Fatal Error: Unable to Decode JSON

The PHP error "Call to undefined function json_decode()" indicates that the JSON parsing function is not recognized by PHP. Despite the reported PHP version being higher than 5.1, which includes JSON support, this error may still occur.

Debian's Removal of the JSON Extension

In Debian-based systems, including Ubuntu, the standard JSON extension has been removed from PHP 5.5rc2 due to a licensing conflict. Debian requires all packaged software to comply with the Debian Free Software Guidelines (DFSG).

JSON Licensing Issues

The original JSON license contains a clause that restricts its use for "Good, not Evil." This conflicts with the DFSG's definition of free software, which requires the freedom to run the program for any purpose. As such, Debian considers the JSON license to be nonfree.

Replacement PHP Extension

Debian has replaced the standard JSON extension with a functionally equivalent replacement that complies with the DFSG. To resolve the "json_decode()" error, Debian users need to install the appropriate replacement extension for their PHP version:

• sudo apt-get install php7.2-json (PHP 7.2)


• sudo apt-get install php7.1-json (PHP 7.1)


• sudo apt-get install php5-json (PHP 5.x)

Apache Restart

After installing the required extension, it's crucial to restart Apache or PHP-FPM to activate the changes:

• sudo service apache2 restart (Apache)


• sudo service php7.2-fpm restart (PHP-FPM 7.2)

Additional Information

• Iteration 99 on the JSON Licensing Issue


• Lior Kaplan's Farewell to the Non-Free Extension


• PHP Bug Report on the Removal of JSON


• Confirmation of JSON's Availability in PHP 5.5

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