I have run into the situation where I needed to transfer a WordPress Multisite twice now, My first experience was horrific, but it seems I have a better handle on this now.
Step 1: Back everything up
Should be pretty self-explanatory — back up your files and database in preparation to transfer. DO NOT copy the .htaccess and wp-config.php files, it’s better practice to set these up from scratch.
Step 2: Copy the files to your new server/location
Send over your files to the new location via FTP, SSH, SVN, whatever. Create your database and set up your wp-config.php file.
Step 3: Go through WordPress installation
Before you import your database, go through the steps to set up the WP site from a clean install. Go through the steps to setting up a WPMU. This way the code you need to stick into your .htaccess and wp-config.php files will have the proper rewrite rules, as well as DOMAIN_CURRENT_SITE and PATH_CURRENT_SITE definitions.
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