Thank you UFHH01, I've no issue only since the defualt session path on plesk php is "/var/lib/php/session" where no application is working since only root user has access, it is working for me when I'm changing that path to a path where my application user has access.
anyway, it is only a question on a public forum.
i'm using latest plesk "12.5.30 Update #40" installed on centos 7 and magento 2.1 istalled using plesk application pool.
Regards..