What happens when we click Upgrade Now?
- WordPress creates automatically a file named .maintenance
- All these files might be overriden:
- All the files under /wp-includes/
- All the files under /wp-admin/
- Any wordpress’ original theme folder (Twentyten, Twentyeleven etc..) under wp_content/
- All files directly under wordpress’ root
- A couple of files/folders may be added to wp_content/
- On the database, The “db_upgraded” flag on the wp_options table is set to “0”
- If all went well, WordPress deletes automatically the .maintenance file
Once done, the right db and system versions are recorded on the wp_config.php file:
* The WordPress version string
* @global string $wp_version
$wp_version = '3.1.3';
* Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
* @global int $wp_db_version
$wp_db_version = 17516;
If anything goes wrong – here’s an interesting article with some suggestions for troubleshooting.