How to set session.save_path?

For educational purpose, I want to change my session.save_path
I think I set path properly, but no file is created in the folder.
I tested following codes :

// test/index.php

<?php session_save_path(getcwd().'/sess'); session_start(); echo getcwd().'
'; echo session_save_path(); ?>

and result is as following (I hid my account information with *)


Output seems to have no problem, but no file is created at that folder.

Is it prohibited to change session save path? If not, how can I change my session save path properly?

Nevermind. It is set properly, and some session files are created in that folder.
Removing cookies did the work.