[root@ ~]# netstat -nat | awk 'FNR>2{print $NF}' | sort | uniq -c
5 ESTABLISHED
9 LISTEN
1 TIME_WAIT
参数说明：
netstat -nat 参数t表示只列出tcp连接
awk 'FNR>2{print $NF}' FNR表示这条记录的行号，NF表示这一条记录中的字段总数
TCP连接状态的定义：
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.