netstat 是Linux系统管理常用的一个命令，尤其是在进行网络相关问题排查的时候更是堪称‘瑞士***’。本人一直以来也只是对常用的几个选项如（a 、n、 p、 t、 u）等几个选项较为熟悉，但是对于netstat显示出来的连接的 状态信息，如下图
多数还了解的不够透彻，今天有时间，特此照着man文档加深一下理解。
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netstat – Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
SYNOPSIS（概要） netstat [address_family_options（地址族选项）] [–tcp|-t] [–udp|-u] [–raw|-w] [–listening|-l] [–all|-a] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–sym-bolic|-N] [–extend|-e[–extend|-e]] [–timers|-o] [–program|-p] [–verbose|-v] [–continuous|-c] [delay] netstat {–route|-r} [address_family_options] [–extend|-e[–extend|-e]] [–verbose|-v] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continu-ous|-c] [delay] netstat {–interfaces|-I|-i} [iface] [–all|-a] [–extend|-e] [–verbose|-v] [–program|-p] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continu-ous|-c] [delay] netstat {–groups|-g} [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continuous|-c] [delay] netstat {–masquerade|-M} [–extend|-e] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continuous|-c] [delay] netstat {–statistics|-s} [–tcp|-t] [–udp|-u] [–raw|-w] [delay] netstat {–version|-V} netstat {–help|-h} address_family_options: [–protocol={inet,unix,ipx,ax25,netrom,ddp}[,…]] [–unix|-x] [–inet|–ip] [–ax25] [–ipx] [–netrom] [–ddp]NOTE This program is obsolete. Replacement for netstat is ss. Replacement for netstat -r is ip route. Replacement for netstat -i is ip -s link. Replacement for netstat -gis ip maddr.注：这个程序已经是是老旧的/废弃的了（但是依然很常用）。新版本的系统以ss命令来替代netstat，以ip route来替代netstat -r，以ip maddr来替代netstat -g。
DESCRIPTION（摘要） Netstat prints information about the Linux networking subsystem. The type of information printed is controlled by the first argument, as follows: netstat 打印Linux网络子系统的信息，输出的信息样式由第一个参数来控制，如下：(none) By default, netstat displays a list of open sockets. If you don’t specify any address families, then the active sockets of all configured address families will beprinted. （无参数）默认的，netstat显示所有系统套接字的列表。如果你不指定任何的地址族，所有的被配置的地址族的活动套接字将会被显示。 –route , -r Display the kernel routing tables. 显示内核路由表 –groups , -g Display multicast group membership information for IPv4 and IPv6. 显示IPv4和IPv6的多播组成员信息。 –interfaces=iface , -I=iface , -i Display a table of all network interfaces, or the specified iface. 显示所有网络接口的信息表，或者显示指定的接口 –masquerade , -M Display a list of masqueraded connections. 显示伪装的连接 –statistics , -s Display summary statistics for each protocol. 按照协议类型显示各协议的汇总信息
OPTIONS（选项） –verbose , -v Tell the user what is going on by being verbose. Especially print some useful information about unconfigured address families. –numeric , -n Show numerical addresses instead of trying to determine symbolic host, port or user names. –numeric-hosts shows numerical host addresses but does not affect the resolution of port or user names. –numeric-ports shows numerical port numbers but does not affect the resolution of host or user names. –numeric-users shows numerical user IDs but does not affect the resolution of host or port names. –protocol=family , -A （协议族类型） Specifies the address families (perhaps better described as low level protocols) for which connections are to be shown. family is a comma (’,’) separated list of addressfamily keywords like inet, unix, ipx, ax25, netrom, and ddp. This has the same effect as using the –inet, –unix (-x), –ipx, –ax25, –netrom, and –ddp options. The address family inet includes raw, udp and tcp protocol sockets.
三亚呀——赴一个蓝天碧海。只是微笑地固执自己的坚持，
