WordPress Permalinks Return 404 After a Migration

Short answer: if the home page works but every inner page returns 404, WordPress is running but the server is not passing pretty URLs to it. The content is intact; the URL-rewriting layer moved badly.

Why the home page is the exception

The home page is served at the site root, which needs no rewriting. Every other URL — posts, pages, categories, archives — depends on a rewrite rule that hands the request to WordPress. When those rules are missing or ignored, only the root survives, which is exactly the pattern you see.

Fix it in the right order

1. Confirm the Site and WordPress addresses in Settings › General match the new domain exactly, protocol included.
2. Go to Settings › Permalinks and click Save without changing anything — this regenerates the rewrite rules and, on Apache, rewrites .htaccess.
3. On Apache, confirm AllowOverride All is set so .htaccess is actually read; on Nginx, confirm the try_files ... /index.php?$args rule is present, since Nginx has no .htaccess.
4. Clear every cache layer, including the CDN, before re-testing.

Check for mixed old URLs too

A migration that broke permalinks often left absolute references to the old domain in the database. Those do not cause 404s alone, but they produce broken images, mixed-content warnings and odd redirects. Fix them with a search-and-replace that understands serialised data — WP-CLI’s wp search-replace 'oldurl' 'newurl' --skip-columns=guid — not a plain-text find and replace, which corrupts serialised arrays.

Verify

Test a post, a page, a category archive, a paginated listing and search. Then confirm the admin works and that no URL silently redirects back to the previous domain.