How to check if mod rewrite is enabled on your server
From Joomla! Documentation
Many problems with search engine optimization arise from the fact that a host has not enabled the Apache setting mod_rewrite. They often tell you they have while they have not. You can verify if this is correct and if this is causing your server to issue HTTP Error 500.
Here is how to check if mod_rewrite is really enabled.
1. Enable SEO in your Administrator.
Set Site → Global Configuration → SEO Settings → Search Engine Friendly URLs to Yes. Set URL Rewriting to Yes. (Setting Add suffix to URLs is optional).
2. Rename your htaccess.txt to .htaccess
Next place only the following lines in your .htaccess file:
RewriteEngine On Options +FollowSymLinks RewriteRule ^joomla\.html http://www.joomla.org/? [R=303,L]
3. Now point your browser to https://www.example.com/joomla.html
(Replace www.example.com with your own domain name in the URL above.)
If it redirects you to joomla.org then mod_rewrite is working. If it gives you an error, mod_rewrite is not working.
Note if your site is located in a folder such as /test, you need to insert the code in the root .htaccess file as follows:
RewriteEngine On Options +FollowSymLinks RewriteRule ^test/joomla\.html http://www.joomla.org/? [R=303,L]