Using Permalinks « WordPress Codex

Using Permalinks « WordPress Codex: "WordPress can't update your .htaccess file automatically, it will tell you something like If your .htaccess file were writable, we could do this automatically, but it isn’t… near the bottom of the Settings → Permalinks panel.

If you want to let WordPress do this, you'll need to give WordPress write access to the .htaccess file. The exact permissions necessary depend on your server setup. Try adding write permissions for the owner, then group, then world, testing after each change; once WordPress has edited the file successfully, don't add any further write permissions.

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