resolv.conf文件中有search項時，主機名解析規則順序：
DNS配置文件如下：
# vi /etc/resolv.conf # Generated by NetworkManager search openstack.local dev.com example.local nameserver 192.168.122.21例1：查詢主機名，因為主機名后面沒有點，就認為是主機名，所以先添加search里的每一項依次組成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 centos7-bind-1 Trying "centos7-bind-1.openstack.local" Trying "centos7-bind-1.dev.com" Trying "centos7-bind-1.example.local" Trying "centos7-bind-1" ;; connection timed out; no servers could be reached
例2：查詢主機名，因為主機名中有點（不是末尾有點），就認為是完全合格域名，先用它來查詢，查詢失敗就把它當成是主機名來進行，添加search里的每一項組成FQDN（完全合格域名）來查詢。
# host -a centos7-bind-1.com Trying "centos7-bind-1.com" Received 109 bytes from 192.168.122.21#53 in 177 ms Trying "centos7-bind-1.com.openstack.local" Trying "centos7-bind-1.com.dev.com" Trying "centos7-bind-1.com.example.local" Host centos7-bind-1.com not found: 3(NXDOMAIN) Received 125 bytes from 192.168.122.21#53 in 55 ms
例3：查詢主機名，因為主機名中末尾有點，則認為是完全合格域名，只用它來查詢（不會再添加search里的每一項）。查詢次數會與search里項域名個數有關。
# host -a centos7-bind-1. Trying "centos7-bind-1" ;; connection timed out; trying next origin Trying "centos7-bind-1" ;; connection timed out; trying next origin Trying "centos7-bind-1" ;; connection timed out; trying next origin Trying "centos7-bind-1" ;; connection timed out; no servers could be reached
DNS查詢工具：host命令介紹
用法：host [-a] FQDN [server]
host -l domain [server]
-a參數：顯示查詢的所有詳細信息。
-l參數：如果后面的domain允許allow-transfer時，則列出該domain所管理的所有主機數據。
server參數：這個參數可有可無，當想要利用非 /etc/resolv.conf 內的DNS主機，來查詢主機名與 IP 的對應時，就可以利用這個參數了。
host命令使用例（列出該domain所管理的所有主機數據）：
# host -l example.local 192.168.122.84 Using domain server: Name: 192.168.122.84 Address: 192.168.122.84#53 Aliases: example.local name server ns.example.local. dns.example.local has address 192.168.123.10 ns.example.local has address 192.168.122.84 ns.example.local has IPv6 address ::1 sss.example.local has address 192.168.123.9 www.example.local has address 192.168.123.8