linux修改DNS本地缓存

1.安装dnsmasq；
2.设定dnsmasq接管本机的DNS解析请求，修改/etc/dnsmasq.conf，确保listen-address=127.0.0.1；
3.修改dhclient的配置，确保prepend domain-name-servers 127.0.0.1;
4.修改resolv.conf的配置，确保nameserver 127.0.0.1排第1；
5.重启dnsmasq服务。
验证：

DevOps nova # dig pkgs.org

; <<>> DiG 9.10.3-P4-Ubuntu <<>> pkgs.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60235
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2

;; QUESTION SECTION:
;pkgs.org. IN A

;; ANSWER SECTION:
pkgs.org. 600 IN A 144.76.64.139

;; AUTHORITY SECTION:
pkgs.org. 83756 IN NS ns2.pkgs.org.
pkgs.org. 83756 IN NS ns.pkgs.org.

;; ADDITIONAL SECTION:
ns.pkgs.org. 82424 IN A 144.76.64.139
ns2.pkgs.org. 36910 IN A 193.201.116.2

;; Query time: 67 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Thu Nov 24 11:55:39 CST 2016
;; MSG SIZE rcvd: 109

DevOps nova # dig pkgs.org

; <<>> DiG 9.10.3-P4-Ubuntu <<>> pkgs.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29324
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1280
;; QUESTION SECTION:
;pkgs.org. IN A

;; ANSWER SECTION:
pkgs.org. 595 IN A 144.76.64.139

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Thu Nov 24 11:55:44 CST 2016
;; MSG SIZE rcvd: 53