netstat 的10個基本用法

2017-03-23 17:39:01 ? ? 來源：? ? 點擊：0

Netstat 簡介

Netstat 是一款命令行工具，可用于列出系統(tǒng)上所有的網絡套接字連接情況，包括 tcp, udp 以及 unix 套接字，另外它還能列出處于監(jiān)聽狀態(tài)（即等待接入請求）的套接字。如果你想確認系統(tǒng)上的 Web 服務有沒有起來，你可以查看80端口有沒有打開。以上功能使 netstat 成為網管和系統(tǒng)管理員的必備利器。在這篇教程中，我會列出幾個例子，教大家如何使用 netstat 去查找網絡連接信息和系統(tǒng)開啟的端口號。

以下的簡單介紹來自 netstat 的 man 手冊：

netstat - 打印網絡連接、路由表、連接的數據統(tǒng)計、偽裝連接以及廣播域成員。

1. 列出所有連接

第一個要介紹的，是最簡單的命令：列出所有當前的連接。使用 -a 選項即可。

$?netstat?-a?Active?Internet?connections?(servers?and?established)Proto?Recv-Q?Send-Q?Local?Address???????????Foreign?Address?????????State??????tcp????????0??????0?enlightened:domain??????*:*?????????????????????LISTEN?????tcp????????0??????0?localhost:ipp???????????*:*?????????????????????LISTEN?????tcp????????0??????0?enlightened.local:54750?li240-5.members.li:http?ESTABLISHEDtcp????????0??????0?enlightened.local:49980?del01s07-in-f14.1:https?ESTABLISHEDtcp6???????0??????0?ip6-localhost:ipp???????[::]:*??????????????????LISTEN?????udp????????0??????0?enlightened:domain??????*:*????????????????????????????????udp????????0??????0?*:bootpc????????????????*:*????????????????????????????????udp????????0??????0?enlightened.local:ntp???*:*????????????????????????????????udp????????0??????0?localhost:ntp???????????*:*????????????????????????????????udp????????0??????0?*:ntp???????????????????*:*????????????????????????????????udp????????0??????0?*:58570?????????????????*:*????????????????????????????????udp????????0??????0?*:mdns??????????????????*:*????????????????????????????????udp????????0??????0?*:49459?????????????????*:*????????????????????????????????udp6???????0??????0?fe80::216:36ff:fef8:ntp?[::]:*?????????????????????????????udp6???????0??????0?ip6-localhost:ntp???????[::]:*?????????????????????????????udp6???????0??????0?[::]:ntp????????????????[::]:*?????????????????????????????udp6???????0??????0?[::]:mdns???????????????[::]:*?????????????????????????????udp6???????0??????0?[::]:63811??????????????[::]:*?????????????????????????????udp6???????0??????0?[::]:54952??????????????[::]:*?????????????????????????????Active?UNIX?domain?sockets?(servers?and?established)Proto?RefCnt?Flags???????Type???????State?????????I-Node???Pathunix??2??????[?ACC?]?????STREAM?????LISTENING?????12403????@/tmp/dbus-IDgfj3UGXXunix??2??????[?ACC?]?????STREAM?????LISTENING?????40202????@/dbus-vfs-daemon/socket-6nUC6CCx

上述命令列出 tcp, udp 和 unix 協(xié)議下所有套接字的所有連接。然而這些信息還不夠詳細，管理員往往需要查看某個協(xié)議或端口的具體連接情況。

2. 只列出 TCP 或 UDP 協(xié)議的連接

使用?-t?選項列出 TCP 協(xié)議的連接：

$?netstat?-atActive?Internet?connections?(servers?and?established)Proto?Recv-Q?Send-Q?Local?Address???????????Foreign?Address?????????State??????tcp????????0??????0?enlightened:domain??????*:*?????????????????????LISTEN?????tcp????????0??????0?localhost:ipp???????????*:*?????????????????????LISTEN?????tcp????????0??????0?enlightened.local:36310?del01s07-in-f24.1:https?ESTABLISHEDtcp????????0??????0?enlightened.local:45038?a96-17-181-10.depl:http?ESTABLISHEDtcp????????0??????0?enlightened.local:37892?ABTS-North-Static-:http?ESTABLISHED.....

使用?-u?選項列出 UDP 協(xié)議的連接：

$?netstat?-auActive?Internet?connections?(servers?and?established)Proto?Recv-Q?Send-Q?Local?Address???????????Foreign?Address?????????State??????udp????????0??????0?*:34660?????????????????*:*????????????????????????????????udp????????0??????0?enlightened:domain??????*:*????????????????????????????????udp????????0??????0?*:bootpc????????????????*:*????????????????????????????????udp????????0??????0?enlightened.local:ntp???*:*????????????????????????????????udp????????0??????0?localhost:ntp???????????*:*????????????????????????????????udp????????0??????0?*:ntp???????????????????*:*????????????????????????????????udp6???????0??????0?fe80::216:36ff:fef8:ntp?[::]:*?????????????????????????????udp6???????0??????0?ip6-localhost:ntp???????[::]:*?????????????????????????????udp6???????0??????0?[::]:ntp????????????????[::]:*

上面同時顯示了 IPv4 和 IPv6 的連接。

3. 禁用反向域名解析，加快查詢速度

默認情況下 netstat 會通過反向域名解析技術查找每個 IP 地址對應的主機名。這會降低查找速度。如果你覺得 IP 地址已經足夠，而沒有必要知道主機名，就使用?-n?選項禁用域名解析功能。

$?netstat?-antActive?Internet?connections?(servers?and?established)Proto?Recv-Q?Send-Q?Local?Address???????????Foreign?Address?????????State??????tcp????????0??????0?127.0.1.1:53????????????0.0.0.0:*???????????????LISTEN?????tcp????????0??????0?127.0.0.1:631???????????0.0.0.0:*???????????????LISTEN?????tcp????????0??????0?192.168.1.2:49058???????173.255.230.5:80????????ESTABLISHEDtcp????????0??????0?192.168.1.2:33324???????173.194.36.117:443??????ESTABLISHEDtcp6???????0??????0?::1:631?????????????????:::*????????????????????LISTEN

上述命令列出所有 TCP 協(xié)議的連接，沒有使用域名解析技術。So easy ? 非常好。

4. 只列出監(jiān)聽中的連接

任何網絡服務的后臺進程都會打開一個端口，用于監(jiān)聽接入的請求。這些正在監(jiān)聽的套接字也和連接的套接字一樣，也能被 netstat 列出來。使用?-l?選項列出正在監(jiān)聽的套接字。

$?netstat?-tnlActive?Internet?connections?(only?servers)Proto?Recv-Q?Send-Q?Local?Address???????????Foreign?Address?????????State??????tcp????????0??????0?127.0.1.1:53????????????0.0.0.0:*???????????????LISTEN?????tcp????????0??????0?127.0.0.1:631???????????0.0.0.0:*???????????????LISTEN?????tcp6???????0??????0?::1:631?????????????????:::*????????????????????LISTEN

現(xiàn)在我們可以看到處于監(jiān)聽狀態(tài)的 TCP 端口和連接。如果你查看所有監(jiān)聽端口，去掉?-t?選項。如果你只想查看 UDP 端口，使用?-u?選項，代替?-t?選項。

注意：不要使用?-a?選項，否則 netstat 會列出所有連接，而不僅僅是監(jiān)聽端口。

5. 獲取進程名、進程號以及用戶 ID

查看端口和連接的信息時，能查看到它們對應的進程名和進程號對系統(tǒng)管理員來說是非常有幫助的。舉個栗子，Apache 的 httpd 服務開啟80端口，如果你要查看 http 服務是否已經啟動，或者 http 服務是由 apache 還是 nginx 啟動的，這時候你可以看看進程名。

使用?-p?選項查看進程信息。

~$?sudo?netstat?-nlptActive?Internet?connections?(only?servers)Proto?Recv-Q?Send-Q?Local?Address???????????Foreign?Address?????????State???????PID/Program?nametcp????????0??????0?127.0.1.1:53????????????0.0.0.0:*???????????????LISTEN??????1144/dnsmasq????tcp????????0??????0?127.0.0.1:631???????????0.0.0.0:*???????????????LISTEN??????661/cupsd???????tcp6???????0??????0?::1:631?????????????????:::*????????????????????LISTEN??????661/cupsd

使用?-p?選項時，netstat 必須運行在 root 權限之下，不然它就不能得到運行在 root 權限下的進程名，而很多服務包括 http 和 ftp 都運行在 root 權限之下。

相比進程名和進程號而言，查看進程的擁有者會更有用。使用?-ep?選項可以同時查看進程名和用戶名。

$?sudo?netstat?-ltpeActive?Internet?connections?(only?servers)Proto?Recv-Q?Send-Q?Local?Address???????????Foreign?Address?????????State???????User???????Inode???????PID/Program?nametcp????????0??????0?enlightened:domain??????*:*?????????????????????LISTEN??????root???????11090???????1144/dnsmasq????tcp????????0??????0?localhost:ipp???????????*:*?????????????????????LISTEN??????root???????9755????????661/cupsd???????tcp6???????0??????0?ip6-localhost:ipp???????[::]:*??????????????????LISTEN??????root???????9754????????661/cupsd

上面列出 TCP 協(xié)議下的監(jiān)聽套接字，同時顯示進程信息和一些額外信息。

這些額外的信息包括用戶名和進程的索引節(jié)點號。這個命令對網管來說很有用。

注意?- 假如你將?-n?和?-e?選項一起使用，User 列的屬性就是用戶的 ID 號，而不是用戶名。

6. 打印統(tǒng)計數據

netstat 可以打印出網絡統(tǒng)計數據，包括某個協(xié)議下的收發(fā)包數量。

下面列出所有網絡包的統(tǒng)計情況：

$?netstat?-sIp:????32797?total?packets?received????0?forwarded????0?incoming?packets?discarded????32795?incoming?packets?delivered????29115?requests?sent?out????60?outgoing?packets?droppedIcmp:????125?ICMP?messages?received????0?input?ICMP?message?failed.????ICMP?input?histogram:????????destination?unreachable:?125????125?ICMP?messages?sent????0?ICMP?messages?failed????ICMP?output?histogram:????????destination?unreachable:?125...?OUTPUT?TRUNCATED?...

如果想只打印出 TCP 或 UDP 協(xié)議的統(tǒng)計數據，只要加上對應的選項（-t?和?-u）即可，so easy。

7. 顯示內核路由信息

使用?-r?選項打印內核路由信息。打印出來的信息與 route 命令輸出的信息一樣。我們也可以使用?-n?選項禁止域名解析。

$?netstat?-rnKernel?IP?routing?tableDestination?????Gateway?????????Genmask?????????Flags???MSS?Window??irtt?Iface0.0.0.0?????????192.168.1.1?????0.0.0.0?????????UG????????0?0??????????0?eth0192.168.1.0?????0.0.0.0?????????255.255.255.0???U?????????0?0??????????0?eth0

8. 打印網絡接口

netstat 也能打印網絡接口信息，-i?選項就是為這個功能而生。

$?netstat?-iKernel?Interface?tableIface???MTU?Met???RX-OK?RX-ERR?RX-DRP?RX-OVR????TX-OK?TX-ERR?TX-DRP?TX-OVR?Flgeth0???????1500?0?????31611??????0??????0?0?????????27503??????0??????0??????0?BMRUlo????????65536?0??????2913??????0??????0?0??????????2913??????0??????0??????0?LRU

上面輸出的信息比較原始。我們將?-e?選項和?-i?選項搭配使用，可以輸出用戶友好的信息。

$?netstat?-ieKernel?Interface?tableeth0??????Link?encap:Ethernet??HWaddr?00:16:36:f8:b2:64????????????inet?addr:192.168.1.2??Bcast:192.168.1.255??Mask:255.255.255.0??????????inet6?addr:?fe80::216:36ff:fef8:b264/64?Scope:Link??????????UP?BROADCAST?RUNNING?MULTICAST??MTU:1500??Metric:1??????????RX?packets:31682?errors:0?dropped:0?overruns:0?frame:0??????????TX?packets:27573?errors:0?dropped:0?overruns:0?carrier:0??????????collisions:0?txqueuelen:1000???????????RX?bytes:29637117?(29.6?MB)??TX?bytes:4590583?(4.5?MB)??????????Interrupt:18?Memory:da000000-da020000??lo????????Link?encap:Local?Loopback????????????inet?addr:127.0.0.1??Mask:255.0.0.0??????????inet6?addr:?::1/128?Scope:Host??????????UP?LOOPBACK?RUNNING??MTU:65536??Metric:1??????????RX?packets:2921?errors:0?dropped:0?overruns:0?frame:0??????????TX?packets:2921?errors:0?dropped:0?overruns:0?carrier:0??????????collisions:0?txqueuelen:0???????????RX?bytes:305297?(305.2?KB)??TX?bytes:305297?(305.2?KB)

上面的輸出信息與 ifconfig 輸出的信息一樣。

9. netstat 持續(xù)輸出

我們可以使用 netstat 的?-c?選項持續(xù)輸出信息。

$?netstat?-ct

這個命令可持續(xù)輸出 TCP 協(xié)議信息。

10. 顯示多播組信息

選項?-g?會輸出 IPv4 和 IPv6 的多播組信息。

$?netstat?-gIPv6/IPv4?Group?MembershipsInterface???????RefCnt?Group---------------?------?---------------------lo??????????????1??????all-systems.mcast.neteth0????????????1??????224.0.0.251eth0????????????1??????all-systems.mcast.netlo??????????????1??????ip6-allnodeslo??????????????1??????ff01::1eth0????????????1??????ff02::fbeth0????????????1??????ff02::1:fff8:b264eth0????????????1??????ip6-allnodeseth0????????????1??????ff01::1wlan0???????????1??????ip6-allnodeswlan0???????????1??????ff01::1

更多用法

目前為止我們列出了 netstat 的基本用法，現(xiàn)在讓我們一起來 geek 吧～

打印 active 狀態(tài)的連接

active 狀態(tài)的套接字連接用 "ESTABLISHED" 字段表示，所以我們可以使用 grep 命令獲得 active 狀態(tài)的連接：

$?netstat?-atnp?|?grep?ESTA(Not?all?processes?could?be?identified,?non-owned?process?info?will?not?be?shown,?you?would?have?to?be?root?to?see?it?all.)tcp????????0??????0?192.168.1.2:49156???????173.255.230.5:80????????ESTABLISHED?1691/chrome?????tcp????????0??????0?192.168.1.2:33324???????173.194.36.117:443??????ESTABLISHED?1691/chrome

配合 watch 命令監(jiān)視 active 狀態(tài)的連接：

$?watch?-d?-n0?"netstat?-atnp?|?grep?ESTA"

查看服務是否在運行

如果你想看看 http,smtp 或 ntp 服務是否在運行，使用 grep。

$?sudo?netstat?-aple?|?grep?ntpudp????????0??????0?enlightened.local:ntp???*:*?????????????????????????????????root???????17430???????1789/ntpd???????udp????????0??????0?localhost:ntp???????????*:*?????????????????????????????????root???????17429???????1789/ntpd???????udp????????0??????0?*:ntp???????????????????*:*?????????????????????????????????root???????17422???????1789/ntpd???????udp6???????0??????0?fe80::216:36ff:fef8:ntp?[::]:*??????????????????????????????root???????17432???????1789/ntpd???????udp6???????0??????0?ip6-localhost:ntp???????[::]:*??????????????????????????????root???????17431???????1789/ntpd???????udp6???????0??????0?[::]:ntp????????????????[::]:*??????????????????????????????root???????17423???????1789/ntpd???????unix??2??????[?]?????????DGRAM????????????????????17418????1789/ntpd

從這里可以看到 ntp 服務正在運行。使用 grep 命令你可以查看 http 或 smtp 或其它任何你想查看的服務。

好了，netstat 的大部分功能都介紹過了，如果你想知道 netstat 更高級的功能，閱讀它的手冊吧（man netstat）。

歡迎在下面留下你的反饋和建議。

轉載于:https://blog.51cto.com/163572/1909903

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