使用命令time dig google.com

看到域名解析需要1秒多

real    0m1.037s
user    0m0.016s
sys     0m0.012s

查看文件/etc/resolv.conf内容

现在这是一个链接文件

lrwxrwxrwx 1 root root 29 Nov 20 07:55 /etc/resolv.conf -> ../run/resolvconf/resolv.conf

cat /etc/resolv.conf 
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 192.168.1.1
nameserver 8.8.8.8
nameserver 8.8.4.4
search localdomain

因为服务器是LAN和WAN都通过dhcp获取地址

resolvconf在设置naneserver的时候把内网的IP设置在最前面了

导致第一次查询失败

通过修改文件/etc/resolvconf/interface-order来调整nameserver的顺序

查看文件/etc/resolvconf/interface-order原始的内容

# interface-order(5)
lo.inet*
lo.dnsmasq
lo.pdnsd
lo.!(pdns|pdns-recursor)
lo
tun*
tap*
hso*
em+([0-9])?(_+([0-9]))*
p+([0-9])p+([0-9])?(_+([0-9]))*
eth*
ath*
wlan*
ppp*
*

外网使用了网桥br0，默认内容里没有网桥接口

所以需要在eth*前面增加br*

以便resolvconf脚本把WAN口通过DHCP获取的DNS服务器设置在前面

执行sudo resolvconf -u

可以看到/etc/resolv.conf中nameserver的顺序变化

执行time dig google.com

real    0m0.042s
user    0m0.016s
sys     0m0.012s

查看相关手册

man 8 resolvconf

man 5 resolv.conf

man 5 interface-order