I just ran the script installer upgrade for MediaWiki on all virtual servers. After the upgrades were done, the title pages of all wikis show
MediaWiki 1.31 internal error MediaWiki 1.31 requires at least PHP version 7.0.0 or HHVM version 3.18.5, you are using PHP 5.5.9-1ubuntu4.25. Supported PHP versions Please consider upgrading your copy of PHP. PHP versions less than 5.6.0 are no longer supported by the PHP Group and will not receive security or bugfix updates. If for some reason you are unable to upgrade your PHP version, you will need to download an older version of MediaWiki from our website. See ourcompatibility page for details of which versions are compatible with prior versions of PHP.
A script installer upgrade must show a warning, before it is leaving a software in an unusable state.
Is there a way to downgrade all MedaWiki instances to the last working version?