mysql - PHP 实现机器在线与否。
有机器，PHP做后台，机器开机的时候会访问服务器，此时将状态置为『上线』，但是下线因为好多机器都是直接断电，所以不会访问后台，这样的话怎么去修改机器的状态呢？
回复内容：
有机器，PHP做后台，机器开机的时候会访问服务器，此时将状态置为『上线』，但是下线因为好多机器都是直接断电，所以不会访问后台，这样的话怎么去修改机器的状态呢？
机器在运行的时候，定期给后台发送心跳包，告诉后台我还在线，后台每隔一段时间做一次检查，把没收到心跳包的机器当做下线处理，不知道这样能否满足你的需求
（1）离线检测：在服务端开一个crontab，每隔一段时间对机器列表轮询发ping包，然后把掉线的机器置成下线状态。
（2）实时检测：如果这个后台只是用于展示机器是否还在线的状态，可以在展示机器列表的时候，实时发ping包检测机器是否在线。这种方式只能满足实时展示机器是否在线的需求，并且存在性能问题。
做个定时轮询吧！
可以用socket吧
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