Checking Apache mod rewrite
If after you installed osCommerce 4.x you fail to open the admin page or the pages under Sales Channels tab cannot be opened the fact that mod_rewrite does not work may cause this issue.
In order to check that mod_rewrite is enabled and works correctly perform the following actions:
1. Open the root directory (or admin directory if you fail to open the admin page) of your website, create a file check_mod_rewrite.php with the following line:
<?php echo "<h1>Mod_rewrite is working well</h1>";
2. Rename the original file from .htacess to .htacess_original
3. Create a new .htaccess file with the following line:
RewriteRule ^.*$ check_mod_rewrite.php
4. Open your web site (or /admin page). If you see a message “Mod_rewrite is working well”, it is ok. If you see anything else - mod_rewrite is disabled or incorrectly configured.
5. Delete the .htaccess file you created and rename the original file back.