Linux netstat 命令入门知识

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。netstat - Print network connections, routing tables, interface statistics, masquerade connections, and multicast membershipsSYNOPSIS（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 [--unix|-x] [--inet|--ip] [--ax25] [--ipx] [--netrom] [--ddp]NOTEThis program is obsolete.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 , -rDisplay the kernel routing tables.显示内核路由表--groups , -gDisplay 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 , -iDisplay 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 , -MDisplay a list of masqueraded connections.显示伪装的连接--statistics , -sDisplay 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 , -vTell 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-hostsshows numerical host addresses but does not affect the resolution of port or user names.--numeric-portsshows numerical port numbers but does not affect the resolution of host or user names.--numeric-usersshows 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.-c, --continuousThis will cause netstat to print the selected information every second continuously（连续不断的）.-e, --extendDisplay additional information. Use this option twice for maximum detail.显示更多的信息，用-ee 显示最多的信息-o, --timersInclude information related to networking timers.显示和网络计时器相关的信息-p, --programShow the PID and name of the program to which each socket belongs.显示连接所属的PID和程序名称-l, --listeningShow only listening sockets. (These are omitted by default.)只显示监听的套接字（端口）默认是忽略这个选项的-a, --allShow both listening and non-listening (for TCP this means established connections) sockets. With the --interfaces option, show interfaces that are not marked-FPrint routing information from the FIB. (This is the default.)-CPrint routing information from the route cache.-Z --contextIf SELinux enabled print SELinux context.-T --notrimStop trimming long addresses.delayNetstat will cycle printing through statistics every delay seconds接下来是重头戏了，深入理解netstat的输出，这里才是实际能帮助我们、给我们提示的地方。本文来自：Linux学习网