（用以解决USB摄像头不识别的状况）
rpi-update是老外开发的一个更新树莓派firmware的工具
$ sudo apt-get update
$ sudo apt-get install ca-certificates
$ sudo apt-get install git-core
$ sudo wget -O /usr/bin/rpi-update
$ sudo chmod +x /usr/bin/rpi-update
$ sudo rpi-update
“
Raspberry Pi firmware updater by Hexxeh, enhanced by AndrewS
Performing self-update
Autodetecting memory split
Using ARM/GPU memory split of 192MB/64MB
We're running for the first time
Setting up firmware (this will take a few minutes)
Using SoftFP libraries
/opt/vc/sbin/vcfiled: error while loading shared libraries:libvchiq_arm.so: cannot open shared object file: No such file or directory
If no errors appeared, your firmware was successfully setup
A reboot is needed to activate the new firmware
”
这里先不重启，再输入：
$ sudo ldconfig
$ sudo rpi-update
“
Raspberry Pi firmware updater by Hexxeh, enhanced by AndrewS
Performing self-update
Autodetecting memory split
Using ARM/GPU memory split of 192MB/64MB
Updating firmware (this will take a few minutes)
Your firmware is already up to date
”
重启：
$ sudo reboot
重启过后
$ ls /dev
发现有video0了