/etc/resolv.conf檔案中的search項作用

resolv.conf檔案中有search項時，主機名解析規則順序：
DNS配置檔案如下：

# cat /etc/resolv.conf 
; generated by /usr/sbin/dhclient-script
search aqiyi.domain aqiyi.virtual ksc.com
nameserver 8.8.8.8

例1：查詢主機名，因為主機名後面沒有點，就認為是主機名，所以先新增search裡的每一項依次組成FQDN（完全合格域名）來查詢，完全合格域名查詢未找到，就再認為主機名是完全合格域名來查詢。

# host -a testttttttttt
Trying 
 
"testttttttttt.aqiyi.domain"
Trying "testttttttttt.aqiyi.virtual"
Trying "testttttttttt.ksc.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14314
;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;testttttttttt.ksc.com.        IN    ANY

;; ANSWER SECTION:
testttttttttt.ksc.com.    
 
3599    IN    A    69.172.201.153
testttttttttt.ksc.com.    3599    IN    NS    ns1.uniregistrymarket.link.
testttttttttt.ksc.com.    3599    IN    NS    ns2.uniregistrymarket.link.
testttttttttt.ksc.com.    3599    IN    SOA    ns1.uniregistrymarket.link. hostmaster.hostingnet.com. 1555555555 10800 3600 604800
 
 86400
testttttttttt.ksc.com.    3599    IN    MX    1 mx247.in-mx.com.
testttttttttt.ksc.com.    3599    IN    MX    1 mx247.in-mx.net.

Received 230 bytes from 8.8.8.8#53 in 625 ms

例2：查詢主機名，因為主機名中有點（不是末尾有點），就認為是FQDN（完全合格域名）來查詢。

# host -a testttttttttt.com
Trying "testttttttttt.com"
Host testttttttttt.com not found: 3(NXDOMAIN)
Received 108 bytes from 8.8.8.8#53 in 43 ms
Received 108 bytes from 8.8.8.8#53 in 43 ms

如何保持resolv.conf檔案內容不被修改 (CentOS7)

當檔案被dhcp服務管理時。通過dhcp配置檔案設定dns地址和預設搜尋域

# vim etc/dhcp/dhclient.conf 
interface "eth0" {
    supersede domain-name-servers  8.8.8.8 ;
    supersede domain-name "aqiyi.domain aqiyi.virtual" ;
}

cat /etc/resolv.conf 
; generated by /usr/sbin/dhclient-script
search aqiyi.domain aqiyi.virtual
nameserver 8.8.8.8