PHP Warning Permission denied (13) on session_start()

I would check that the permissions on:

/Users/alvincrespo/Sites/apollo/storage/views/26bdebca7505781c753aa21663170a1b

Allow your application to write to this directory.

Assuming you are on a linux box you could run ls -l to see what the permissions are, and if it is set to read only, change the permissions with chmod.

You can modify another users session (see below), although personally, I would recommend against it. As I imagine it can open up a whole world of session hijacking and other vulnerabilities.

With your example use case

A common user is logged, while in the same time an administrator uses the Admin functions and change some value for this user. If the value is not something obtained from the database every time, the session variable for that current logged in user need to have its value changed.

You would be better of updating the value in the database and then just checking to see if it's changed before you process the next page. If you don't want to be checking multiple user fields before each page load then when you update the user in the admin panel, you can build a hash of the values and add it to a new column called session_hash. Then just compare this field on page load

But if you still want to modify another user's session, you can set your current session_id to the targets.

// End my current session and save its id
session_start();
$my_session_id = session_id();
session_write_close();

// Modify our target session 
session_id($target_id);
session_start();
$_SESSION['is_logged_in'] = false;
session_write_close();

// Start our old session again
session_id($my_session_id);
session_start();

EDIT

Example: https://www.samdjames.uk/session_example/index.php

Example Src: https://gist.github.com/SamJUK/c220e3742487567c6262238edf85695e