To add the X-Clacks-Overhead header to Apache, the Header directive can be added to the Apache configuration file or the .htaccess file.
After setting up the header, verify it works.
Header set X-Clacks-Overhead "GNU Robbert Muller"
systemctl restart apache2, apache2ctl restart, service apache2 restart, or similar command..htaccess File.htaccess in the root directory of the webroot, if one doesn't already exist..htaccess file:
<IfModule headers_module>
Header set X-Clacks-Overhead "GNU Robbert Muller"
</IfModule>
.htaccess file.A server restart is usually not needed for these changes to take effect.