TCP的各种状态信息描述

$ man  netstat
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   State

       All standard TCP states: established, syn-sent, syn-recv, fin-wait-1, fin-wait-2, time-wait, closed, close-wait, last-ack, listen and closing.

       The  state of the socket. Since there are no states in raw mode and usually no states used in UDP and UDPLite, this column may be left blank. Normally this can be one of sev‐
       eral values:

       ESTABLISHED
              The socket has an established connection.

       SYN_SENT
              The socket is actively attempting to establish a connection.

       SYN_RECV
              A connection request has been received from the network.

       FIN_WAIT1
              The socket is closed, and the connection is shutting down.

       FIN_WAIT2
              Connection is closed, and the socket is waiting for a shutdown from the remote end.

       TIME_WAIT
              The socket is waiting after close to handle packets still in the network.

       CLOSE  The socket is not being used.

       CLOSE_WAIT
              The remote end has shut down, waiting for the socket to close.

       LAST_ACK
              The remote end has shut down, and the socket is closed. Waiting for acknowledgement.

       LISTEN The socket is listening for incoming connections.  Such sockets are not included in the output unless you specify the --listening (-l) or --all (-a) option.

       CLOSING
              Both sockets are shut down but we still don't have all our data sent.

       UNKNOWN
              The state of the socket is unknown.

ESTABLISHED       socket已经建立连接

CLOSED            socket没有被使用，无连接

CLOSING           服务器端和客户端都同时关闭连接

CLOSE_WAIT        等待关闭连接

TIME_WAIT         表示收到了对方的FIN报文，并发送出了ACK报文，等待2MSL后就可回到CLOSED状态

LAST_ACK         远端关闭，当前socket被动关闭后发送FIN报文，等待对方ACK报文

LISTEN            监听状态

SYN_RECV          接收到SYN报文

SYN_SENT          已经发送SYN报文

FIN_WAIT1         连接正在关闭

FIN_WAIT2         正在等待来自远端的关闭