For OpenCart v2.1.0.2 the following folder permissions should either be 755 or 777. The following folder permissions should be changed:
/var/www/html/interiors/image/ /var/www/html/interiors/image/cache/ /var/www/html/interiors/image/catalog/ /var/www/html/interiors/system/storage/cache/ /var/www/html/interiors/system/storage/logs/ /var/www/html/interiors/system/storage/download/ /var/www/html/interiors/system/storage/upload/ /var/www/html/interiors/system/storage/modification/