linux vps提供商的vps大多数都是mini版或者精简版，并没有自带dig命令，这时我们需要手动安装dig命令。
linux下安装使用dig命令，debian和centos可用
debian系统
apt-get install dnsutils
centos系统
yum install bind-utils
dig命令大多时候可以取代nslookup
dig命令支持A\AAA\CNAME\NS\MX\TXT等常见类型，使用方法也非常简单
简明使用，只会输出A记录(写脚本的时候容易获取ip地址)
root@iZwz9avyv2945ilt432lffZ:~# dig a ixmu.net ; <<>> DiG 9.10.3-P4-Debian <<>> a ixmu.net ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52501 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;ixmu.net. IN A ;; ANSWER SECTION: ixmu.net. 300 IN A 59.56.78.44 ;; Query time: 12 msec ;; SERVER: 100.100.2.136#53(100.100.2.136) ;; WHEN: Mon Nov 02 15:00:44 CST 2020 ;; MSG SIZE rcvd: 53
大部分的时候dig最下面显示了查询所用的时间及DNS服务器，时间，数据大小。DNS超时时间为30秒，查询时间对于排查DNS问题很有用。
;; Query time: 48 msec ;; SERVER: 10.202.72.118#53(10.202.72.118) ;; WHEN: Sun Oct 12 21:41:47 2014 ;; MSG SIZE rcvd: 225
DNS的解析是递规解析，那么用dig可以加+trace参数，会显示完整的，无缓存，递规的查询，显示的是完整的trace记录。
root@iZwz9avyv2945ilt432lffZ:~# dig ixmu.com +trace ; <<>> DiG 9.10.3-P4-Debian <<>> ixmu.com +trace ;; global options: +cmd . 1849 IN NS c.root-servers.net. . 1849 IN NS j.root-servers.net. . 1849 IN NS i.root-servers.net. . 1849 IN NS f.root-servers.net. . 1849 IN NS e.root-servers.net. . 1849 IN NS m.root-servers.net. . 1849 IN NS k.root-servers.net. . 1849 IN NS h.root-servers.net. . 1849 IN NS d.root-servers.net. . 1849 IN NS l.root-servers.net. . 1849 IN NS b.root-servers.net. . 1849 IN NS g.root-servers.net. . 1849 IN NS a.root-servers.net. . 88981 IN RRSIG NS 8 0 518400 20201110050000 20201028040000 26116 . xhiiRZWRQD18irvY5WWQyTBqQOIAoIgEwpvasTy1rlAOBD14LNwKLTDz sdG8YGN1fYm0I02lilrQ2hdOzbVVKQJee9oqTKIx3OIEOMfWkfMxnIcg UvjkVhSYgYO+hqjzoI+C53s4qoesvnuXBXjnHtYiZE0pRUoAQ0MYxNpk 0wnIfyomhyzzCcZe2eJdqydO+w53gtJ6AQU3bvL3DTBe3GYxkGx9BP27 AKgOEBCVL3QOUXtEqIHJ23RhxZHzLKRB1HTYGkb1QZyib0/+9EMzhKga 8qHiVThFAJ+sZjLEVw4R2nlQCgX1Ki2yNM4hxj4/Wd0CwQQOj4foZADu ngAnbQ== ;; Received 525 bytes from 100.100.2.136#53(100.100.2.136) in 0 ms com. 172800 IN NS a.gtld-servers.net. com. 172800 IN NS b.gtld-servers.net. com. 172800 IN NS c.gtld-servers.net. com. 172800 IN NS d.gtld-servers.net. com. 172800 IN NS e.gtld-servers.net. com. 172800 IN NS f.gtld-servers.net. com. 172800 IN NS g.gtld-servers.net. com. 172800 IN NS h.gtld-servers.net. com. 172800 IN NS i.gtld-servers.net. com. 172800 IN NS j.gtld-servers.net. com. 172800 IN NS k.gtld-servers.net. com. 172800 IN NS l.gtld-servers.net. com. 172800 IN NS m.gtld-servers.net. com. 86400 IN DS 30909 8 2 E2D3C916F6DEEAC73294E8268FB5885044A833FC5459588F4A9184CF C41A5766 com. 86400 IN RRSIG DS 8 1 86400 20201115050000 20201102040000 26116 . a1cgYDa/OC+sOdqBEjcL1AHwBnjVpTfC9lG4hNWAM6EFvwDDv3c0Z2P0 ae64cpTTu1uWdX7OGT9R/EHH1PXRGlbAmRMcMq2kpPaZy6oJpQkEOJQe wtyfVftlfGbo0P2VqznFs4+6yWNHnESO0pD/c6Wg3j9wBvDlnF2Oi9g/ hOPzo+NNMQ7lZboeRhGFiERdf5dikmKi1v+WAttAk1MgdL8hv9WfjZYN 8PEI/ndGOL8Fz8n8r/mQhkn36r/Pc573auXNdgxOqnH4ntVP77E7J5lF ywvnEIU+fPxICsFH0VEGKE/1nthTYYMRh7kW8bHuvI9flu2mlTvY0rTN 86/RsQ== ;; Received 1168 bytes from 192.58.128.30#53(j.root-servers.net) in 215 ms ixmu.com. 172800 IN NS ns1.hasns.com. ixmu.com. 172800 IN NS ns2.hasns.com. ixmu.com. 172800 IN NS ns3.hasns.com. ixmu.com. 172800 IN NS ns4.hasns.com. CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN NSEC3 1 1 0 - CK0Q1GIN43N1ARRC9OSM6QPQR81H5M9A NS SOA RRSIG DNSKEY NSEC3PARAM CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN RRSIG NSEC3 8 2 86400 20201109054042 20201102043042 31510 com. AQ/C247BFFWm7+G8mOcyTBflc19nk/0ymEf+tlKfkW8Mx1YE+7I5OobP BXAqpm6jvHsVH1zYH4JGZxrWdqbgrJeb8jKK21iUJrz+SXHRabY8LSlv y8xfz2UZeHB4EcBFWm17C1JarZv8+rBNMVqZJ39cofhjDSTguCxrn4Zr e69TaLxNLhfGZ3Vgon2hv3dGg91/CQcjzeu3XCda6pR3Aw== 0D09K5OVGRFRL42ERNAFORG9SR9AC82E.com. 86400 IN NSEC3 1 1 0 - 0D09U39F25BAGD9P57LMJ54A0OA2ILQJ NS DS RRSIG 0D09K5OVGRFRL42ERNAFORG9SR9AC82E.com. 86400 IN RRSIG NSEC3 8 2 86400 20201105074215 20201029053215 31510 com. X6LPpYTu++sdNo4mW2o7SKQ9Bov2jhTaPxRDPqkNiGRUXhLGpBvlf2Bz efo7LJIqx2U/S6+hRKTY6twt8YFuQl5oQF0G0jETa1xOMSeW6NMPaKA2 3rJkTqGLaMZ2fTLRFsQFTEWp5aoDA3E+yK8sSba0f5VQLFuJJ0Jr0Ys2 PHcEQrGuVPUPrm2CXubgNf16D4m70vMDyGKPpAJfLy97eg== ;; Received 728 bytes from 192.55.83.30#53(m.gtld-servers.net) in 215 ms ixmu.com. 3600 IN A 104.219.168.162 ixmu.com. 3600 IN NS ns2.hasns.com. ixmu.com. 3600 IN NS ns1.hasns.com. ixmu.com. 3600 IN NS ns3.hasns.com. ixmu.com. 3600 IN NS ns4.hasns.com. ;; Received 131 bytes from 172.104.243.104#53(ns2.hasns.com) in 217 ms
服务器上很多时候是双线或三线，如果有智能解析的话要测试从某一个 ip 去请求 dns，加 -b 参数
root@iZwz9avyv2945ilt432lffZ:~# dig -b 172.17.17.91 ixmu.net ; <<>> DiG 9.10.3-P4-Debian <<>> -b 172.17.17.91 ixmu.net ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7333 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;ixmu.net. IN A ;; ANSWER SECTION: ixmu.net. 300 IN A 59.56.78.44 ;; Query time: 7 msec ;; SERVER: 100.100.2.136#53(100.100.2.136) ;; WHEN: Mon Nov 02 15:03:41 CST 2020 ;; MSG SIZE rcvd: 53
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