Raspberry Pi Wifi Static IP

My RPi is going to be a telepresence robot so it uses wifi. It also needs a static IP address. Here's how to configure Raspbian Wheezy with a static IP for wifi using WPA2 personal with PSK (Private Shared Key). The changes to your /etc/network/interfaces file will result in something like the following.

auto lo

iface lo inet loopback
iface eth0 inet static
address 192.168.0.5
netmask 255.255.255.0
gateway 192.168.0.1

auto wlan0
allow-hotplug wlan0
iface wlan0 inet static
address 192.168.0.4
netmask 255.255.255.0
gateway 192.168.0.1
wpa-passphrase yourpassphrasehere
wpa-ssid yourssidhere
wireless-channel yourchannelhere

#wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
#iface default inet dhcp

Specify using static instead of manual for interface wlan0, then specify the address, netmask, and gateway, configure the WPA passphrase and SSID, and the wireless channel. Finally, you have to disable the wpa_supplicant configuration, and you have to disable the default dhcp behavior.

Finally, you can either reboot, or you can issue the following commands to restart the wlan0 interface

sudo ifdown wlan0
sudo ifup wlan0

If you get no errors on the last command, except possibly some ioctl errors, you're a-ok.

pi@raspberrypi:/etc/network$ sudo ifup wlan0
ioctl[SIOCSIWAP]: Operation not permitted
ioctl[SIOCSIWENCODEEXT]: Invalid argument
ioctl[SIOCSIWENCODEEXT]: Invalid argument
pi@raspberrypi:/etc/network$

Double-check by issuing ifconfig wlan0, make sure it's configured correctly, then issue a ping to your gateway (ping 192.168.0.1) and then ping google.com or some other reliable website.

pi@raspberrypi:/etc/network$ ifconfig -a
eth0      Link encap:Ethernet  HWaddr b8:27:eb:fb:8d:50
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:36 errors:0 dropped:0 overruns:0 frame:0
          TX packets:36 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:3480 (3.3 KiB)  TX bytes:3480 (3.3 KiB)

wlan0     Link encap:Ethernet  HWaddr 80:1f:02:86:ef:61
          inet addr:192.168.0.4  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:38 errors:0 dropped:1467 overruns:0 frame:0
          TX packets:14 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:841044 (821.3 KiB)  TX bytes:100717 (98.3 KiB)

pi@raspberrypi:/etc/network$ ping 192.168.0.1
PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data.
64 bytes from 192.168.0.1: icmp_req=1 ttl=64 time=3.07 ms
64 bytes from 192.168.0.1: icmp_req=2 ttl=64 time=1.90 ms
^C
--- 192.168.0.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 1.905/2.491/3.077/0.586 ms
^C

Et voila, you have a wifi static IP. Congratulations!