PHP Fatal error: Cannot redeclare normalizer_is_normalized()

FAQ
1

Symptom

PHP Fatal error: Cannot redeclare normalizer_is_normalized() when using the occ upgrade command

Environment

owncloud server 10.5

Steps to reproduce

  1. Run the command sudo -u www-data php occ upgrade -v during the upgrade of your owncloud server to 10.6
  2. Notice the error PHP Fatal error: Cannot redeclare normalizer_is_normalized()

Cause

Issue with the php version used

Solution/Workaround

Make sure to meet the system requirement for ownCloud 10.6 version.
For more details please check the following link : https://doc.owncloud.com/server/admin_manual/release_notes.html#changes-in-10-6-0

So If you’re running on PHP < 7.3, please make sure to schedule an upgrade to PHP 7.4

References