Unable to find writable var_dir

#0 /var/www/app/code/core/Mage/Core/Model/Config/Options.php(60): Mage_Core_Model_Config_Options->getVarDir()
#1 /var/www/lib/Varien/Object.php(94): Mage_Core_Model_Config_Options->_construct()
#2 /var/www/app/code/core/Mage/Core/Model/Config.php(192): Varien_Object->__construct()
#3 /var/www/app/Mage.php(591): Mage_Core_Model_Config->__construct()
#4 /var/www/index.php(81): Mage::run('', 'store')
#5 {main}