Here’s my stripped-down set of steps for converting individual WordPress installations to a single Multisite installation. Read the full article with commentary for a good laugh at my expense.

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I assembled the following list of steps by capturing individual tasks from multiple articles on sticky notes as I researched. Then I arranged the steps into a more-or-less logical order.

I’m sure there are missing steps and a better order to do them in, so feedback to improve these instructions is welcome.

Steps To Migrate to WordPress Multisite

1. Identify what problems you are trying to solve.
2. Determine if WPMU will solve those problems.
3. Check out alternatives to Multisite as part of due diligence.
4. Do an inventory of your sites to see whether and how many efficiencies can be realized, i.e. is it worth the effort. My inventory looks like this:
   
5. Confirm whether there are WPMU-compatible versions of the plugins and themes you want to use.
6. Understand the basic steps involved in migrating to WPMU. Ask:
   • Am I technically capable of doing those things?
   • Do I have the necessary tools and access to do those things?
   • Can I get help if I get stuck?
   • Am I fine with sites being down for awhile if I get stuck?
   • Am I fine with starting over from scratch in case something goes horribly, terribly, disastrously wrong?
   • Does my web hosting service support WPMU?
7. If yes to all of the above, then carry on.
8. Do a deeper read of any steps specific to your situation.
   • For example, find out if your sites need to have different IP addresses for whatever reason (for example SEO). (WPMU doesn’t seamlessly support this.)
9. Decide on subdomain vs. folder configuration. (Default for converting existing site is subdomain.)
10. Write down or screenshot any plugin settings needed.
11. Create a wildcard sub domain via your web host.
12. Delete quarantined spam comments — no need to bring those forward.
13. Use https://sucuri.net/ to ensure your site hasn’t been hacked or infected before backing everything up.
14. Back up everything.
15. Disable plugins so they can’t interfere with the migration except for whatever plugin you may be using to export.
16. Export contents of each WordPress install using either a plugin or native WP Export (Tools > Export) to create and/or verify a WXR and/or an XML file.
17. Edit the wp-config file per instructions to activate Multisite.
18. Use Tools > Network Setup > Install Multisite.
19. Backup then add lines to wp-config and .htaccess files per instructions.
20. Clear the cache and cookies.
21. Log in again.
22. Go to My Sites > Network Admin > Sites > Add New.
23. Create subsite1.mainsite.com and any other subsites you need.
24. Decide on a default theme until the others get installed (I used Twenty-Seventeen).
25. Install themes used by sites (MU compatible versions) > Network Enable.
26. Install plugins used by sites (MU compatible) > Network Enable.
27. Delete dummy content, comments and widgets to get empty sites.
28. Install WordPress Importer plugin > Network Enable.
29. Import XML files (Tools > Import > WP > Run) into the appropriate subsites.
30. Choose how to handle imported users and post assignments.
31. Choose to download and import attachments.
32. Check to see that everything got imported correctly.
33. Map domain names to their new sites using native WP domain name hookup or WP MU Domain Mapping plugin. (Sorry, I don’t have better instructions here because I didn’t do it correctly myself.)
34. Uninstall any plugins used for the migration that are no longer needed.
35. Clean up any backup or temporary files used during the migration
36. Uninstall the separate WP installations
37. Check that all is well after doing that.
38. Go through “hardening WP” steps to secure your sites.
39. Clean up extra users for each site and change passwords for them.
40. Log into each website’s dashboard and make sure all is in order.

Resources

A few of the many, many, many helpful resources I consulted:

• Before You Create A Network – WordPress Codex
• Taylor McCaslin: Best Friend or Worst Enemy – Multisite Do’s and Don’ts (video)
• 7 Tools To Manage Multiple Sites From Single Dashboard
• The Ultimate Guide to WordPress Multisite
• The Ultimate Guide to Domain Mapping with WordPress and Multisite
• WordPress Security: The Ultimate Guide

WordPress sticker image courtesy of wpmxday on Flickr / hiveminer.com