本文介绍如何使用discoveryutil工具清理MAC OS（Yosemite）的DNS缓存，啥是DNS这里就不赘述了:)
你需要使用终端（Terminal）来清理DNS缓存，可以用Spotlight启动终端或者从/Applications/Utilities/里面找到，最终目标是清理MDNS和UDNS两种DNS缓存。
首先：打开MAC OS terminal
Control+Spase 输入：终端
然后在终端执行 discoveryutil 命令：
清理 MDNS (Multicast DNS) Cache
sudo discoveryutil mdnsflushcache
回车，需要输入管理员密码
清理 UDNS(Unicast DNS) Cache
sudo discoveryutil udnsflushcaches
回车，需要输入管理员密码
一步清理OS X Yosemite所有DNS缓存
sudo discoveryutil mdnsflushcache;sudo discoveryutil udnsflushcaches;say flushed
执行后没有返回结果输出：
MacBook-Pro:~ sudops.com$ sudo discoveryutil mdnsflushcache;sudo discoveryutil udnsflushcaches;say flushed Password: MacBook-Pro:~ sudops.com$
下面是查看现有的cache MDNS/UDNS情况：
sudo discoveryutil mdnscachestats sudo discoveryutil udnscachestats
我的执行结果如下：
MacBook-Pro:~ sudops.com$ sudo discoveryutil udnscachestats UDNS Cache Stats: Ext Resolver on en1 UDNS Cache Stats: Resolver domain [default], type Unicast, ifIndex 6, port 0, timeout 30, A yes, AAAA no, serviceID 0, scope None, order 0 server(s) 8.8.8.8, 8.8.4.4 UDNS Cache Stats: Cached 115 of 5000, table size 256, hash coverage 0.22, max miss depth 8, avg miss depth 0.38, reclaims 0 Cached records after aging 89 UDNS Cache Stats: Ext Resolver on en1 UDNS Cache Stats: Resolver domain [default], type Unicast, ifIndex 6, port 0, timeout 30, A yes, AAAA no, serviceID 0, scope InterfaceID, order 0 server(s) 8.8.8.8, 8.8.4.4 UDNS Cache Stats: Cached 0 of 5000, table size 256, hash coverage 0.00, max miss depth 0, avg miss depth 0.00, reclaims 0 Cached records after aging 0
看到我的DNS服务器是：8.8.8.8, 8.8.4.4，
UDNS缓存状态：UDNS Cache Stats: Cached 115 of 5000, table size 256, hash coverage 0.22 …
MacBook-Pro:~ sudops.com$ sudo discoveryutil mdnscachestats MDNS Cache Stats: lo0: Cached 0 of 7500, table size 16, hash coverage 0.00, max miss depth 0, avg miss depth 0.00, reclaims 0 Cached records after aging 0 MDNS Cache Stats: vboxnet0: Cached 0 of 7500, table size 256, hash coverage 0.00, max miss depth 0, avg miss depth 0.00, reclaims 0 Cached records after aging 0 MDNS Cache Stats: awdl0: Cached 0 of 7500, table size 256, hash coverage 0.00, max miss depth 0, avg miss depth 0.00, reclaims 0 Cached records after aging 0 MDNS Cache Stats: en1: Cached 0 of 7500, table size 128, hash coverage 0.00, max miss depth 0, avg miss depth 0.00, reclaims 0 Cached records after aging 0
最后可以使用dig/nslookup命令查询域名的解析情况：
如：
dig google.com
MacBook-Pro:~ sudops.com$ dig google.com ; <<>> DiG 9.8.3-P1 <<>> google.com ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46653 ;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 4, ADDITIONAL: 4 ;; QUESTION SECTION: ;google.com. IN A ;; ANSWER SECTION: google.com. 74 IN A 74.125.23.100 google.com. 74 IN A 74.125.23.101 google.com. 74 IN A 74.125.23.102 google.com. 74 IN A 74.125.23.113 google.com. 74 IN A 74.125.23.138 google.com. 74 IN A 74.125.23.139 ...
