Download and transfer the source code of Raspberry Pi

In the steps, the source code of Raspberry Pi in GitHub (linux and firmware) are downloaded to a host PC running Ubuntu, then copy to Raspberry Pi.

• - In Host PC side -
  Because the source code of Raspberry Pi is too large, and too long time to download, it will be done in another host pc.
  
  - Create git directory to hold the files.
  $ mkdir git
  $ cd git
  
  - git clone the source code.
  $ git clone https://github.com/raspberrypi/linux
  $ git clone https://github.com/raspberrypi/firmware
  
  It take long time to finish.
• - In Host PC side -, after downloaded:
  - Compress and copy to Pi, under /home/pi.
  $ tar -cvf linux.tar.gz --exclude .git linux
  $ scp linux.tar.gz pi@raspberrypi:/home/pi
  
• - In Pi side -, switch to /home/pi directory
  $ tar -xvf linux.tar.gz
  $ cd linux
  $ zcat /proc/config.gz > .config
  $ make oldconfig
  $ make modules_prepare
  
• - In host PC side -, host PC: copy Module.symvers to pi's linux directory.
  $ scp firmware/extra/Module.symvers pi@raspberrypi:/home/pi/linux
  
• - In Pi side -, move linux directory to /usr/src/kernels/$(uname -r)
  $ sudo mkdir /usr/src/kernels
  $ cd ~
  $ sudo mv linux /usr/src/kernels/$(uname -r)
  $ cd /lib/modules/$(uname -r)
  
  make links for build and source
  $ sudo ln -s /usr/src/kernels/$(uname -r) build
  $ sudo ln -s /usr/src/kernels/$(uname -r) source