References:

https://source.android.com/source/downloading.html

'Embedded Android' by Karim Yaghmour

Install Repo:

sudo apt-get install curl git
 mkdir ~/bin 
 PATH=~/bin:$PATH
 curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo 
 chmod a+x ~/bin/repo

Initialize a Repo Client:

 mkdir android-AOSP
 cd android-AOSP
 git config --global user.name "Your Name"
 git config --global user.email "you@example.com"  #       |
 # I'll come back to this --------------------------------\ /`
 #                                                         v                 
 repo init -u https://android.googlesource.com/platform/manifest -b android-6.0.1_r78 
 # See page 82 in the book for info about pulling from a branch rather than the master
 repo sync  # Additionally you could use the -j switch  
 # This takes a long time.  It looks to be a 65.6GB download.