[PHP] How to implement this by php Session

[Henry]

I'd like to implement ONE USER SIGNIN at the same time, the way I consider about is 
below:
1 record the sessionId and userId in some media(db), then we'll know who is login 
  and who is not
2 use a demon program to determine whole sessionId which is live and correspond to 
db's 
  data if some session is dead then demon program will remove from db

that's what I think, does it work? or anybody has real exprience about it?
if my idea work, how to get whole live sessionId from webserver(apache+php)?

thanks

RDS