设置树莓派的无线网卡为监听模式(monitor)

先使用命令查看无线网卡的名字：

ifconfig

结果如下：

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.123.165  netmask 255.255.255.0  broadcast 192.168.123.255
        inet6 fe80::8ced:f8c8:81e:4e78  prefixlen 64  scopeid 0x20<link>
        ether b8:27:eb:5f:7f:23  txqueuelen 1000  (Ethernet)
        RX packets 241360939  bytes 36052043728 (33.5 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 533542201  bytes 738621286186 (687.8 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 269480  bytes 11338213 (10.8 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 269480  bytes 11338213 (10.8 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether b8:27:eb:0a:2a:76  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

其中的wlan0就是树莓派自带的无线网卡。
打开无线网卡的监听模式：

ifconfig wlan0 mode monitor

会报错：

mode: Unknown host
ifconfig: `--help' gives usage information.

使用如下命令查看无线网卡是否支持监听模式(monitor)：

iw list

输出结果如下：

        Supported interface modes:
                 * IBSS
                 * managed
                 * AP
                 * P2P-client
                 * P2P-GO
                 * P2P-device

我发现树莓派自带的无线网卡不支持监听模式(monitor)
然后我使用支持监听模式(monitor)的无线网卡，这类网卡有很多，我用的是8187L无线网卡。
然后使用命令

iw list

可以看出支持监听模式(monitor)：

         Supported interface modes:
                 * IBSS
                 * managed
                 * AP
                 * AP/VLAN
                 * monitor
                 * mesh point

开启监听模式(monitor)：

ifconfig wlan1 down
iwconfig wlan1 mode monitor
ifconfig wlan1 up

查看是否成功开启监听模式(monitor)：

iwconfig

结果如下，开启成功：

wlan1     IEEE 802.11  Mode:Monitor  Frequency:2.412 GHz  Tx-Power=30 dBm   
          Retry short  long limit:2   RTS thr:off   Fragment thr:off
          Power Management:off