配置指南：
http://php.net/manual/zh/refs.basic.session.php
http://php.net/manual/zh/session.configuration.php

使用命令：

PHP -i

找到打印输出session块的信息

session

Session Support => enabled
Registered save handlers => files user 
Registered serializer handlers => PHP_serialize PHP PHP_binary 

Directive => Local Value => Master Value
session.auto_start => Off => Off
session.cache_expire => 180 => 180
session.cache_limiter => nocache => nocache
session.cookie_domain => no value => no value
session.cookie_httponly => Off => Off
session.cookie_lifetime => 0 => 0
session.cookie_path => / => /
session.cookie_secure => Off => Off
session.gc_divisor => 100 => 100
session.gc_maxlifetime => 1440 => 1440
session.gc_probability => 1 => 1
session.lazy_write => On => On
session.name => PHPSESSID => PHPSESSID
session.referer_check => no value => no value
session.save_handler => files => files
session.save_path => no value => no value
session.serialize_handler => PHP => PHP
session.sid_bits_per_character => 4 => 4
session.sid_length => 32 => 32
session.upload_progress.cleanup => On => On
session.upload_progress.enabled => On => On
session.upload_progress.freq => 1% => 1%
session.upload_progress.min_freq => 1 => 1
session.upload_progress.name => PHP_SESSION_UPLOAD_PROGRESS => PHP_SESSION_UPLOAD_PROGRESS
session.upload_progress.prefix => upload_progress_ => upload_progress_
session.use_cookies => On => On
session.use_only_cookies => On => On
session.use_strict_mode => Off => Off
session.use_trans_sid => 0 => 0

以及PHP.ini配置的位置

Loaded Configuration File /etc/PHP.ini

接下来配置使用session主要项

在PHP.ini找到以下项并配置启用(去除前面;号，并配置相应的值)

session保存位置

;session.save_path = "/tmp"

session过期时间

session.gc_probability = 1
session.gc_divisor = 1000
session.gc_maxlifetime = 1440

三个属性得结合使用

回收概率：session.gc_probability/session.gc_divisor
即1/1000就是session 1000次才有一次被回收。

只要你的访问量大了,那就能达到回收的效果。

如果你设置session.gc_divisor = 1，过期回收就很明显了

session.gc_maxlifetime单位为 秒，默认1440秒=24分钟