The Exception SessionHandler error may disrupt the last step of the Magento 2 installation. However, you can quickly fix it, regaining control over the procedure and installing Magento 2 successfully. Below, we describe when and why the error occurs and how to fix it. More useful tips are available in our Developer’s Cookbook.
The error occurs only in older code versions. To be more exact, you won’t see this exception working with versions from September 29, 2015, or later.
The session.save_handler PHP parameter set to other session storages than filescauses the issue. For instance, it can be set to redisor memcached. You can leverage one of the following two solutions to install Magento 2 successfully.
Since the problem is caused by the older code versions, you can upgrade it. To update the Magento 2 software:
Use the Component Manager or System Upgrade utilities if you installed the software from an archive or used ‘composer-create-project’