How to find out the session id (I use dbsession) of a user in yii2 and how to work with expire values?

Question

Yii

I use dbsession and see session values ​​in db. Those. configured and configured correctly.
I want to know if the user is online. To do this, I want to take the expire value and compare it with the current time, if it is less than 24 minutes, then the user will be considered as an online user (with an error, of course, but still).
Faced difficulties, namely:
1. How to find out the user's session id by his login, for example?
2. Expire value is just an int number, for example 1427741261, what is this value and how to compare it with the current time?

Answer 1

1. Make your own session component, which writes the user ID in a separate field with an index. Override the writeSession method.
2. This is a UNIX timestamp. Compare as a number.

Answer 2

Use the session_id function.