Mediawiki upgrade
http://www.mediawiki.org/wiki/Manual:Upgrading_to_1.12#Back_up_existing_files_and_the_database
While the upgrade scripts are well-maintained and robust, things could still go pear-shaped. Before proceeding to update the database schema, make a full [1] of the wiki, including both the database and the files:
- the wiki's content, from the database. It may be a good idea to create an XML dump in addition to the SQL database dump.
- text dump: mysqldump --all-databases > file.txt
- xml dump: mysqldump --all-databases --xml > file.xml
- images and other media files (the contents of the images directory)
- configuration files, i.e. LocalSettings.php and AdminSettings.php (if present)
- MediaWiki's program files, including all skins and extensions, especially if you modified them.