You're using Magento 1.9.2.1, so I suggest you to run the following commands to set the right permission for files & directories:

find . -type f -exec chmod 644 {} \;

find . -type d -exec chmod 755 {} \;

When I Install magento 1.9.2.1

Warning: include(/var/www/html/magento1921/lib/Zend/Log.php): failed to open stream: Permission denied in /var/www/html/magento1921/lib/Varien/Autoload.php on line 94

Please help me!