admin/environment/custom check/igbinary version problem
The php-igbinary extension provides an alternative (optimised) serialization mechanism for PHP structures. When available, it can be used by memcached and redis cache stores / session managers.
It has been detected that some recent releases had a bug that can affect Moodle sites in different ways, from not being able to create a session to various problems with the cache stores returning wrong data. Also, some unit tests in those versions will fail because of the bug.
The affected Moodle versions are 3.9.x and 3.10.x. And only when using PHP 7.2.x and php-igbinary >= 3.2.2 and <= 3.2.4.
It's possible to quick-check if your PHP environment is affected with the following (CLI) one-liner:
php -r 'if (!function_exists("igbinary_unserialize")) echo "OK. extension not installed\n"; elseif (key(igbinary_unserialize(igbinary_serialize([0 => 0]))) === 0) echo "OK. extension behaving ok\n"; else echo "PROBLEM. buggy behavior detected!\n";'
Upgrading to PHP 7.3.x or using php-igbinary versions >= 3.2.5 solves the problem.
Some links of interest:
- Moodle Tracker: https://tracker.moodle.org/browse/MDL-72312
- php-igbinary 3.2.5 release: https://github.com/igbinary/igbinary/releases/tag/3.2.5
