Error upgrading Fedora 24 Mediawiki site

Question

Edit 1 - More error information, below:

I normally rebuild systems rather than upgrade them. I first rebuild my system with a virtual machine as a test. I am having a problem with mediawiki.

Working system: Fedora 24, mediawiki 1.26.4-1 php 5.6.27-1

New system: Fedora 25, mediawiki 1.27.1-1 php 7.0.13-1

I have followed the normal process to backup/restore the database and file system that has worked many times before, and ran the upgrade script. Now though, when I pull up the wiki home page I get this error:

Exception encountered, of type "Error"
[WDi085SSXW4b8deWoT2rTgAAAAA] /wiki/ Error from line 161 of /usr/share/mediawiki/includes/session/PHPSessionHandler.php: Class 'Wikimedia\PhpSessionSerializer' not found
Backtrace:
#0 /usr/share/mediawiki/includes/session/SessionManager.php(939): MediaWiki\Session\PHPSessionHandler->setManager(MediaWiki\Session\SessionManager, CachedBagOStuff, MediaWiki\Logger\LegacyLogger)
#1 /usr/share/mediawiki/includes/session/PHPSessionHandler.php(58): MediaWiki\Session\SessionManager->setupPHPSessionHandler(MediaWiki\Session\PHPSessionHandler)
#2 /usr/share/mediawiki/includes/session/PHPSessionHandler.php(120): MediaWiki\Session\PHPSessionHandler->__construct(MediaWiki\Session\SessionManager)
#3 /usr/share/mediawiki/includes/Setup.php(741): MediaWiki\Session\PHPSessionHandler::install(MediaWiki\Session\SessionManager)
#4 /usr/share/mediawiki/includes/WebStart.php(137): require_once(string)
#5 /usr/share/mediawiki/index.php(40): require(string)
#6 {main}

Any suggestions as to troubleshooting this would be appreciated.

Edit 1: More Information:

Note this problem also occurs trying to upgrade mediawiki in place on Fedora 24 as shown by the errors below:

On Screen:

Fatal error: Class 'Wikimedia\PhpSessionSerializer' not found in /usr/share/mediawiki/includes/session/PHPSessionHandler.php on line 161

In httpd log file:

[Fri Dec 02 09:34:26.160621 2016] [:error] [pid 3941] [client ::1:59474] PHP Fatal error:  Class 'Wikimedia\\PhpSessionSerializer' not found in /usr/share/mediawiki/includes/session/PHPSessionHandler.php on line 161
[Fri Dec 02 09:34:26.160666 2016] [:error] [pid 3941] [client ::1:59474] PHP Stack trace:
[Fri Dec 02 09:34:26.160675 2016] [:error] [pid 3941] [client ::1:59474] PHP   1. {main}() /usr/share/mediawiki/index.php:0
[Fri Dec 02 09:34:26.160681 2016] [:error] [pid 3941] [client ::1:59474] PHP   2. require() /usr/share/mediawiki/index.php:40
[Fri Dec 02 09:34:26.160686 2016] [:error] [pid 3941] [client ::1:59474] PHP   3. require_once() /usr/share/mediawiki/includes/WebStart.php:137
[Fri Dec 02 09:34:26.160692 2016] [:error] [pid 3941] [client ::1:59474] PHP   4. MediaWiki\\Session\\PHPSessionHandler::install() /usr/share/mediawiki/includes/Setup.php:742
[Fri Dec 02 09:34:26.160697 2016] [:error] [pid 3941] [client ::1:59474] PHP   5. MediaWiki\\Session\\PHPSessionHandler->__construct() /usr/share/mediawiki/includes/session/PHPSessionHandler.php:120
[Fri Dec 02 09:34:26.160702 2016] [:error] [pid 3941] [client ::1:59474] PHP   6. MediaWiki\\Session\\SessionManager->setupPHPSessionHandler() /usr/share/mediawiki/includes/session/PHPSessionHandler.php:58
[Fri Dec 02 09:34:26.160708 2016] [:error] [pid 3941] [client ::1:59474] PHP   7. MediaWiki\\Session\\PHPSessionHandler->setManager() /usr/share/mediawiki/includes/session/SessionManager.php:939

Answer 1

The wiki move instructions on the MediaWiki site only work if you are moving from and to the EXACT same version of the software.

To do a move/upgrade of a wiki running on Fedora follow these steps:

1. Backup the wiki filesystem and database on the old system as you normally would.
2. On the new system copy the wiki filesystem /var/www/wiki directory into your apache accessible wiki directory (ie /var/www/html/wiki)
3. Restore the /images directory from the old system into the new
4. Restore and/or reinstall any plugins you had on the old system onto the new system
5. Restore the database on the new system
6. Run the maintenance database upgrade script
7. Test the restored wiki