Running Php Script

Running Php Script

i need to keep running the php script.. i have a problem, currently i use
putty to login to the server then execute php code.. when i close putty
session the script stops execution..
steps:
1) login to server with putty
2) running php script eg)php filename
but when i close the putty session the program will obvious close.. i need
to keep running the program on server regardless of closing putty and
anyone logging into server can stop it and run it again as a process.. how
to run a php script independent of putty session, which can be controlled
by anyone logging to server?