netstat

 查看某个端口是否在运行

netstat -tpln | grep 8003

 查看某个端口有多少连接

 netstat -tan | grep 8003|wc -l

查看 socket 状态

State
       The state of the socket. Since there are no states in raw mode and usually no states used in UDP, this column may be left blank. Normally this can be one of several 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.
 
       CLOSED 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.