一、注意和准备
1.1 注意事项
使用无线网卡前请检查电源能否提供足够电压和电流；
使用最新系统：系统增加新网卡的支持，能免去编译驱动的麻烦；
仅针对RaspberryPi 3B以下的设备，这些设备没有配备无线网卡；
请用有线ssh登入，设置过程中树莓派是需要重启无线网络。
1.2 硬件信息
先看我使用的无线网卡：
pi@raspberrypi:~ $ lsusb
Bus 001 Device 004: ID 148f:760b Ralink Technology, Corp. MT7601U Wireless Adapter
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter
Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. SMC9514 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
上面显示的Ralink Technology, Corp. MT7601U Wireless Adapter是我的无线网卡。在Raspbian Stretch Lite 2017-09-07 Kernel 4.9系统镜像中已经自带该网卡的驱动。
如果你的无线网卡在系统中无法识别，请自行编译安装驱动。
1.3 查看已经连接的网络
使用iwconfig查看wlan0的详情：
pi@raspberrypi:~ $ iwconfig
eth0 no wireless extensions.
lo no wireless extensions.
wlan0 IEEE 802.11 ESSID:"NETGEAR76"
Mode:Managed Frequency:2.462 GHz Access Point: 10:DA:43:7A:A3:E8
Bit Rate=24 Mb/s Tx-Power=20 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:off
Link Quality=39/70 Signal level=-71 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:32 Missed beacon:0
上面已经显示了连接到NETGEAR76，连接频段和信号质量等等信息。
二、配置无线网络
2.1 扫描可见SSID
通过sudo iwlist wlan0 scan扫描附近可见的SSID，并截取两个无线路由器的信息。后者NETGEAR76是已经连接的，现用前者MERCURY_4E1A演示。
pi@raspberrypi:~ $ sudo iwlist wlan0 scan
wlan0 Scan completed :
Cell 08 - Address: E4:F3:F5:0F:4E:1A
Channel:11
Frequency:2.462 GHz (Channel 11)
Quality=47/70 Signal level=-63 dBm
Encryption key:on
ESSID:"MERCURY_4E1A"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Mode:Master
Extra:tsf=000004fb6621e986
Extra: Last beacon: 20ms ago
IE: Unknown: 000C4D4552435552595F34453141
IE: Unknown: 010882848B960C121824
IE: Unknown: 03010B
IE: Unknown: 2A0100
IE: Unknown: 32043048606C
IE: Unknown: 2D1A6E1003FFFF000000000000000000000000000000000000000000
IE: Unknown: 3D160B071100000000000000000000000000000000000000
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
IE: WPA Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
IE: Unknown: DD180050F2020101000003A4000027A4000042435E0062322F00
IE: Unknown: DD05000AEB0100
Cell 09 - Address: 10:DA:43:7A:A3:E8
Channel:11
Frequency:2.462 GHz (Channel 11)
Quality=41/70 Signal level=-69 dBm
Encryption key:on
ESSID:"NETGEAR76"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Master
Extra:tsf=00000119cffe47dc
Extra: Last beacon: 20ms ago
IE: Unknown: 00094E4554474541523736
IE: Unknown: 010882840B162430486C
IE: Unknown: 03010B
IE: Unknown: 2A0100
IE: Unknown: 2F0100
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
IE: Unknown: 32040C121860
IE: Unknown: 0B0501001D0000
IE: Unknown: 7F080400080000000040
IE: Unknown: DD7B0050F204104A0001101044000102103B0001031047001021A685A13B70898A47777B80AB552F671021000D4E4554474541522C20496E632E102300055236323530102400055236323530104200033637391054000800060050F2040001101100055236323530100800022008103C0001031049000600372A000120
IE: Unknown: DD090010180201000C0000
IE: Unknown: DD180050F2020101880003A4000027A4000042435E0062322F00
IE: Unknown: 46057208010000
2.2 设置SSID和对应密码
使用命令wpa_passphrase SSID 密码生成SSID和对应的密码，复制内容备用：
pi@raspberrypi:~ $ wpa_passphrase MERCURY_4E1A blackcar
network={
ssid="MERCURY_4E1A"
#psk="blackcar"
psk=7763537e8128e46f91200bab0a3d9adc08d701a0e1a555d0285fd1e10b185ab9
}
或通过重定向命令写入到文件备用:
pi@raspberrypi:~ $ wpa_passphrase MERCURY_4E1A blackcar > ~/wifi.conf
2.3 修改wpa_supplicant.conf
修改wpa_supplicant.conf需要管理员权限，请切换到root:
pi@raspberrypi:~ $ su
Password:
把内容粘贴到/etc/wpa_supplicant/wpa_supplicant.conf：
root@raspberrypi:/home/pi# nano /etc/wpa_supplicant/wpa_supplicant.conf
或重定向的方式给wpa_supplicant.conf追加wifi.conf：
root@raspberrypi:/home/pi# less wifi.conf >> /etc/wpa_supplicant/wpa_supplicant.conf
2.4 配置文件
配置/etc/network/interfaces:
sudo nano /etc/network/interfaces
下面是我的配置，同时支持eth0和wlan0。当网线和Wifi同时连接时会独立获得ip，wlan0的配置表示通过DHCP获取IP地址。
# interfaces(5) file used by ifup(8) and ifdown(8)
# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
auto lo
iface lo inet loopback
allow-hotplug eth0
iface eth0 inet dhcp
allow-hotplug wlan0
auto wlan0
iface wlan0 inet dhcp
pre-up wpa_supplicant -B w -D wext -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf
post-down killall -q wpa_supplicant
2.5 重启网络
设置完成后保存退出，并重启树莓派的的网络：
sudo /etc/init.d/networking restart
sudo ifup wlan0
三、 查看连接后信息
连接成功后，用iwconfig查看信息
pi@raspberrypi:~ $ iwconfig
eth0 no wireless extensions.
lo no wireless extensions.
wlan0 IEEE 802.11 ESSID:"MERCURY_4E1A"
Mode:Managed Frequency:2.437 GHz Access Point: E4:F3:F5:0F:4E:1A
Bit Rate=24 Mb/s Tx-Power=20 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:off
Link Quality=46/70 Signal level=-64 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:5 Missed beacon:0
用ifconfig查看可知获得IP地址：192.168.0.101
pi@raspberrypi:~ $ ifconfig
lo: flags=73 mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10
loop txqueuelen 1 (Local Loopback)
RX packets 8 bytes 312 (312.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 8 bytes 312 (312.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlan0: flags=4163 mtu 1500
inet 192.168.0.101 netmask 255.255.255.0 broadcast 192.168.0.255
inet6 fe80::236:76ff:fe06:8115 prefixlen 64 scopeid 0x20
ether 00:36:76:06:81:15 txqueuelen 1000 (Ethernet)
RX packets 112 bytes 12015 (11.7 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 101 bytes 16500 (16.1 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0