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高版本的Linux自带的OpenSSH在使用的时候，几分钟不操作的话就会自动断开连接，这是出于安全的考虑，但是对于需要长时间使用的用户来说很麻烦，每次都要重新连接。解决方法如下：

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1、echo $TMOUT

如果显示空白,表示没有设置, 等于使用默认值0, 一般情况下应该是不超时. 如果大于0, 可以在如/etc/profile之类文件中设置它为0. Definition: TMOUT: If set to a value greater than zero, the value is interpreted as the number of seconds to wait for input after issuing the primary prompt. Bash terminates after waiting for that number of seconds if input does not arrive 2、修改/etc/ssh/sshd_config文件

将ClientAliveInterval 0和ClientAliveCountMax 3的注释符号去掉,将ClientAliveInterval对应的0改成60,ClientAliveInterval指定了服务器端向客户端请求消息的时间间隔, 默认是0, 不发送.而ClientAliveInterval 60表示每分钟发送一次, 然后客户端响应, 这样就保持长连接了.ClientAliveCountMax, 使用默认值3即可.ClientAliveCountMax表示服务器发出请求后客户端没有响应的次数达到一定值, 就自动断开. 正常情况下, 客户端不会不响应. 想参考更多，请输入man sshd_config了解更多信息

下面是man sshd_config获取的描述信息

ClientAliveInterval:

Sets a timeout interval in seconds after which if no data has been received from the client, sshd will send a message through the encrypted channel to request a response from the client. The default is 0, indicating that these messages will not be sent to the client. This option applies to protocol version 2 only.

ClientAliveCountMax:

Sets the number of client alive messages (see above) which may be sent without sshd receiving any messages back from the client. If this threshold is reached while client alive messages are being sent, sshd will disconnect the client, terminating the session. It is important to note that the use of client alive messages is very different from TCPKeepAlive (below). The client alive messages are sent through the encrypted channel and therefore will not be spoofable. The TCP keepalive option enabled by TCPKeepAlive is spoofable. The client alive mechanism is valuable when the client or server depend on knowing when a connection has become inactive.The default value is 3. If ClientAliveInterval (above) is set to 15, and ClientAliveCountMax is left at the default, unresponsive ssh clients will be disconnected after approximately 45 seconds.

1. 启用putty keepalive

putty -> Connection -> Seconds between keepalives ( 0 to turn off ), 默认为0, 改为60.