linux-netstat输出的网络连接状态信息

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[iyunv@web-nginx-idc0E-node ~]# netstat -n|head  -3
Active Internet connections (w/o servers)
Proto    Recv-Q   Send-Q    Local Address        Foreign Address         State      
tcp        0        52     192.168.1.165:22     192.168.1.10:59337     ESTABLISHED


一共六列:
第一列为socket使用的协议。

[iyunv@web-nginx-idc0E-node1 ~]$ netstat -n |awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
TIME_WAIT 9137
CLOSE_WAIT 207
FIN_WAIT1 547
ESTABLISHED 597
FIN_WAIT2 74
SYN_RECV 70
CLOSING 55
LAST_ACK 8

[iyunv@web-nginx-idc0E-node ~]# man netstat
OUTPUT
Active Internet connections (TCP, UDP, raw)
Proto
The protocol (tcp, udp, raw) used by the socket.
第一列为socket使用的协议。

Recv-Q
The count of bytes not copied by the user program connected to this socket.
第二列为接到的但是还没处理的字节数。

Send-Q
The count of bytes not acknowledged by the remote host.
第三列为已经发送的但是没有被远程主机确认收到的字节数。

Local Address
Address and port number of the local end of the socket.Unless the --numeric(-n)
optionisspecified,thesocketaddress is resolved to its canonical host name
(FQDN), and the port number is translated into the corresponding service name.
第四列为 本地的地址及端口。

Foreign Address
Address and port number of the remote endofthesocket.Analogousto"Local Address."
第五列为外部的地址及端口。


State
Thestateofthesocket.Sincethere 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 sev-
eral values:
第六列为socket的状态，通常仅仅有tcp的状态，状态值可能有ESTABLISHED，SYN_SENT，SYN_RECV FIN_WAIT1，FIN_WAIT2，TIME_WAIT等，详见下文。其中，最重要的是第六列。

ESTABLISHED     established
The socket has an established connection.
socket已经建立连接，表示处于连接的状态，一般认为有一个ESTABLISHED认为是一个服务的并发连接。这个连接状态在生产场景很重要，要重点关注。
SYN_SENT
The socket is actively attempting to establish a connection.
socket正在积极尝试建立一个连接，即处于发送后连接前的一个等待但未匹配进入连接的状态。
SYN_RECV
A connection request has been received from the network.
已经从网络上收到一个连接请求。

FIN_WAIT1
The socket is closed, and the connection is shutting down.
socket已关闭，连接正在或正要关闭。

FIN_WAIT2
Connectionisclosed,andthesocket is waiting for a shutdown from the remote end.
连接已关闭，并且socket正在等待远端结束。

TIME_WAIT
The socket is waiting after close to handle packets still in the network.
socket正在等待关闭处理仍在网络上的数据包，这个连接状态在生产场景很重要，要重点关注。

CLOSED The socket is not being used.| socket不在被占用了。
CLOSE_WAIT
The remote end has shutdown, waiting for the socket to close.
远端已经结束，等待socket关闭。

LAST_ACK
The remote end has shut down, and the socket is closed. Waiting for acknowl-edgement.|
远端已经结束，并且socket也已关闭，等待acknowl-edgement。
LISTEN Thesocketislisteningforincoming connections.Such sockets are not
included in the output unless you specify the --listening (-l) or --all (-a)
option.

socket正在监听连接请求。
CLOSING
Both sockets are shut down but we still don’t have all our data sent.
sockets关闭，但是我们仍旧没有发送数据。
UNKNOWN
The state of the socket is unknown
未知的状态。