My OS is Linux,and when I set the parameter 
session.gc_maxlifetime = 60
It should be expired after 60 seconds,but I found it doesn't work.I also can get varibles once registered and the file is existing, too bad!!
As i think it is maybe because the existence of cookies make the uselessness of session.gc_maxlifetime,I set the session.cookie_lifetime=60,to my surprise,the cookies expired in just 2 minutes and whatever I change the timelimit,it seemed to not about to work and also expired in the exactly 2 minutes,except the customed 0.
That is concerned parameters in php.ini of my computer.


session.save_handler = files

; Argument passed to save_handler.  In the case of files, this is the path
; where data files are stored.
session.save_path = /tmp
; where data files are stored.
session.save_path = /tmp

; Whether to use cookies.
session.use_cookies = 1


; Name of the session (used as cookie name).
session.name = PHPSESSID


; Name of the session (used as cookie name).
session.name = PHPSESSID

; Initialize session on request startup.
session.auto_start = 0

; Lifetime in seconds of cookie or, if 0, until browser is restarted.
session.cookie_lifetime = 0

; The path for which the cookie is valid.
session.cookie_path = /

; The domain for which the cookie is valid.
session.cookie_domain =

; Handler used to serialize data.  php is the standard serializer of PHP.
session.serialize_handler = php

; Percentual probability that the 'garbage collection' process is started
; on every session initialization.
session.gc_probability = 100

; After this number of seconds, stored data will be seen as 'garbage' and
; cleaned up by the garbage collection process.
session.gc_maxlifetime = 60

; Check HTTP Referer to invalidate externally stored URLs containing ids.
session.referer_check =

; How many bytes to read from the file.
session.entropy_length = 0

; Specified here to create the session id.
session.entropy_file =

;session.entropy_length = 16

;session.entropy_file = /dev/urandom
 ; Set to {nocache,private,public} to determine HTTP caching aspects.
session.cache_limiter = nocache

; Document expires after n minutes.
session.cache_expire = 180

; use transient sid support if enabled by compiling with --enable-trans-sid.
session.use_trans_sid = 1

url_rewriter.tags = "a=href,area=href,frame=src,input=src,form=fakeentry"