Session error in magento2

This happens when your session.save_handler PHP parameter is set to some another session storage than files (for example, redis, memcached, and so on). This is a known issue we’re working to resolve.

Solutions:

• Upgrade your Magento 2 code
• Use the following workaround with existing code.

Locate php.ini

Locate php.ini by entering the following command:

php -i | grep "Loaded Configuration File"

Typical locations follow:

• Ubuntu: /etc/php5/cli/php.ini
• CentOS: /etc/php.ini

Workaround

1. As a user with root privileges, open php.ini in a text editor.
2. Locate session.save_handler
3. Set it in any of the following ways:

To comment it out:

;session.save_path = <path>

To set it to a file system path:

session.save_handler = files

References:

1. https://devdocs.magento.com/guides/v2.1/install-gde/trouble/php/tshoot_session.html

2. https://github.com/magento/magento2/issues/5319

I hope this will help