描述：

前段时间在buildroot搭建的根文件系统中移植过wifi驱动并且调试成功，一般来说，buildroot构建的文件系统比较完整，但最近使用busybox来构建了根文件系统，后者就比较简陋，很多文件都是靠自己去创建等等，所以在移植wifi网卡的时候就出现了缺乏某些文件导致功能不能正常使用的问题，现在就记录一下使用busybox里的小工具udhcpc能成功动态获取ip地址，但没能自动设置DNS，也就没能上网的问题。

现象：

...
wlan0: associated
udhcpc: started, v1.32.0
udhcpc: sending discover
udhcpc: sending select for 192.168.1.14
udhcpc: lease of 192.168.1.14 obtained, lease time 3599
/ # 
/ # ifconfig wlan0
wlan0     Link encap:Ethernet  HWaddr 70:F1:1C:27:C6:A4
          inet6 addr: fe80::72f1:1cff:fe27:c6a4/64 Scope:Link
          inet6 addr: 2408:8456:3000:abe4:72f1:1cff:fe27:c6a4/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:28 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:11065 (10.8 KiB)  TX bytes:1832 (1.7 KiB)

/ #

解决：

将busybox-1.xx.x/examples/udhcp/目录下的simple.script文件（注意不是sample.script）拷贝到根文件系统的/usr/share/udhcpc/目录下，将它重命名为default.script，并且chmod +x default.script加上可执行权限即可。

完成之后就可以正常使用了：

...
wlan0: associated
udhcpc: sending discover
udhcpc: sending select for 192.168.1.14
udhcpc: lease of 192.168.1.14 obtained, lease time 3599
Setting IP address 192.168.1.14 on wlan0
Deleting routers
route: SIOCDELRT: No such process
Adding router 192.168.1.228
Recreating /etc/resolv.conf
 Adding DNS server 192.168.1.228
/ #
/ # ifconfig wlan0
wlan0     Link encap:Ethernet  HWaddr 70:F1:1C:27:C6:A4
          inet addr:192.168.1.14  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::72f1:1cff:fe27:c6a4/64 Scope:Link
          inet6 addr: 2408:8456:3000:abe4:72f1:1cff:fe27:c6a4/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:20 errors:0 dropped:0 overruns:0 frame:0
          TX packets:11 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:7416 (7.2 KiB)  TX bytes:1690 (1.6 KiB)

/ #
/ # ping www.baidu.com
PING www.baidu.com (163.177.151.109): 56 data bytes
64 bytes from 163.177.151.109: seq=0 ttl=53 time=47.980 ms
...

参考文章：

• Linux：命令行调试WiFi（iwlist/iwconfig/iw/wpa_supplicant/wpa_cli/dhclient/dhcpd/hostapd/hostapd_cli的使用方法）
• Linux驱动：在imx6ull上适配RT3070 USB WiFi网卡
• 使用udhcpc能获取到DHCP自动分配的IP，但是该IP却没有设置到网卡上