The steps for download android source code. Except for the git tool, all the other steps is for both Windows and Linux.

以下描述是Windows上的操作步骤，其实windows和Linux上面的执行过程没有多大差别，仅在于git安装、Python脚本改成和机器上Python版本相一致。文档最后给出了Linux上获取代码时，执行的所有命令序列。

All the content is referece the link: Windows下载Android源码

1. start git-shell:
2. enter the android folder
3. git clone https://android.googlesource.com/platform/manifest.git
   This will create the manifest directory, and clone the ./manifest/.git directory.
   

hp@HP-PC /e/android
$ git clone https://android.googlesource.com/platform/manifest.git
Cloning into 'manifest'...
remote: Counting objects: 106, done
remote: Finding sources: 100% (106/106)
remote: Total 1030 (delta 144), reused 1030 (delta 144)
Receiving objects: 100% (1030/1030), 895.45 KiB | 498.00 KiB/s, done.
Resolving deltas: 100% (144/144), done.

hp@HP-PC /e/android
$

4. switch to the manifest directory that just cloned.
   And list all the tags by 'git tag'.
   

hp@HP-PC /e/android
$ ls
a.txt       android_src_download_steps.txt  download_src_new.py  recovery-si
android-si  download_src.py                 manifest             src

hp@HP-PC /e/android
$ cd manifest

hp@HP-PC /e/android/manifest (master)
$ git tag
android-1.6_r1.1_
.......
android-4.3_r3.1
android-4.4.1_r1
android-4.4.2_r1
android-4.4.2_r2
android-4.4_r1
android-4.4_r1.1
android-4.4_r1.2
android-cts-2.2_r8
android-cts-2.3_r10
android-cts-2.3_r11
android-cts-2.3_r12
android-cts-4.0.3_r1
android-cts-4.0.3_r2
android-cts-4.0_r1
android-cts-4.1_r1
android-cts-4.1_r2
android-cts-4.2_r2
android-cts-4.4_r1
android-cts-verifier-4.0.3_r1
android-cts-verifier-4.0_r1
android-sdk-4.0.3-tools_r1
android-sdk-4.0.3_r1
android-sdk-4.4.2_r1
android-sdk-adt_r16.0.1
android-sdk-adt_r20
android-sdk-support_r11

hp@HP-PC /e/android/manifest (master)
$

5. check out the android version

hp@HP-PC /e/android/manifest (master)
$ git checkout android-4.4.2_r2
Note: checking out 'android-4.4.2_r2'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b new_branch_name

HEAD is now at 1a5a541... Update manifest for android-4.4.2_r2

hp@HP-PC /e/android/manifest ((android-4.4.2_r2))
$

6. Understand the manifest/default.xml, and write a python script file
   to generate a git-clone file.
   Then execute the .py file, or all the git-clone will start automatically.
   ATTENTION PLS: a. There must be 40G in the disk. b. All the clone will spend many many hours.
   

hp@HP-PC /e/android
$ ls
a.txt       android_4.4.2_r2                download_src.py  recovery-si
android-si  android_src_download_steps.txt  manifest         src

hp@HP-PC /e/android
$ python download_src.py   
C:/Program Files/Git/bin/git.exe clone http://android.googlesource.com/platform/
build.git
Cloning into 'build'...
remote: Sending approximately 23.91 MiB ...
remote: Counting objects: 957, done
remote: Finding sources: 100% (170/170)
Receiving objects:  87% (45093/51754), 9.44 MiB | 210.00 KiB/s   

7. here is the python file as the link that I have referenced.

import xml.dom.minidom
import os
from subprocess import call

#downloaded source path
# if the dir does not exist, it will be created autoomatically as below.
rootdir = "E:/android/android_4.4.2_r2"

#git program path
git="C:/Program Files/Git/bin/git.exe"

dom = xml.dom.minidom.parse("E:/android/manifest/default.xml")
root = dom.documentElement

prefix = git + " clone http://android.googlesource.com/"
suffix = ".git"

if not os.path.exists(rootdir):
    os.mkdir(rootdir)
	
for node in root.getElementsByTagName("project"):
    os.chdir(rootdir)
    d = node.getAttribute("path")
    last = d.rfind("/")
    if last != -1:
        d = rootdir + "/" + d[:last]
        if not os.path.exists(d):
            os.makedirs(d)
        os.chdir(d)
    cmd = prefix + node.getAttribute("name") + suffix
    print cmd
    call(cmd)

附：Linux上下载Android源码的执行命令：

test@myhost /home/test/Android % git clone https://android.googlesource.com/platform/manifest.git
正克隆到 'manifest'...
error: Failed to connect to 2404:6800:4005:c00::52: Network is unreachable while accessing https://android.googlesource.com/platform/manifest.git/info/refs?service=git-upload-pack
fatal: HTTP request failed
129 test@myhost /home/test/Android % git clone https://android.googlesource.com/platform/manifest.git
正克隆到 'manifest'...
remote: Counting objects: 106, done
remote: Finding sources: 100% (106/106)
remote: Total 1030 (delta 144), reused 1030 (delta 144)
接收对象中: 100% (1030/1030), 895.45 KiB | 416 KiB/s, done.
处理 delta 中: 100% (144/144), done.
test@myhost /home/test/Android % ll
总用量 212
-rw-r--r-- 1 test users      2  3月  2 14:34 android_download_source_code_steps.txt
drwxr-xr-x 3 test users   4096  3月  2 14:36 manifest/
-rw-r--r-- 1 test users  35672  3月  1 14:25 python_files.png
drwxr-xr-x 3 test users   4096  3月  1 14:31 Python_Src/
-rw-r--r-- 1 test users 164603  3月  1 16:08 using_authentication.png
test@myhost /home/test/Android % ll ./manifest
总用量 164
-rw-r--r-- 1 test users 21759  3月  2 14:36 base-for-3.0-gpl.xml
-rw-r--r-- 1 test users 22323  3月  2 14:36 base-for-3.1-gpl.xml
-rw-r--r-- 1 test users 23221  3月  2 14:36 base-for-3.2-gpl.xml
-rw-r--r-- 1 test users 45492  3月  2 14:36 base-for-4.2-gpl.xml
-rw-r--r-- 1 test users 40984  3月  2 14:36 default.xml
test@myhost /home/test/Android % cd manifest
test@myhost /home/test/Android/manifest (git)-[master] % git tag
android-1.6_r1.1_
..........
android-4.4.1_r1
android-4.4.2_r1
android-4.4.2_r2
android-4.4_r1
android-4.4_r1.1
android-4.4_r1.2
.................
android-sdk-support_r11
test@myhost /home/test/Android/manifest (git)-[master] % git checkout android-4.4.2_r2
Note: checking out 'android-4.4.2_r2'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b new_branch_name

HEAD 目前位于 1a5a541... Update manifest for android-4.4.2_r2
test@myhost /home/test/Android/manifest (git)-[android-4.4.2_r2] % cd ..
test@myhost /home/test/Android % ll
总用量 216
-rw-r--r-- 1 test users      2  3月  2 14:34 android_download_source_code_steps.txt
-rw-r--r-- 1 test users    855  3月  2 14:41 download_android_src.py
drwxr-xr-x 3 test users   4096  3月  2 14:38 manifest/
-rw-r--r-- 1 test users  35672  3月  1 14:25 python_files.png
drwxr-xr-x 3 test users   4096  3月  1 14:31 Python_Src/
-rw-r--r-- 1 test users 164603  3月  1 16:08 using_authentication.png
test@myhost /home/test/Android % cat download_android_src.py
#! /usr/bin/env python

import xml.dom.minidom  
import os  
from subprocess import call  
  
#downloaded source path  
# if the dir does not exist, it will be created autoomatically as below.  
rootdir = "/home/test/Android/android_4.4.2_r2"  
  
#git program path  
git="git"  
  
dom = xml.dom.minidom.parse("/home/test/Android/manifest/default.xml")  
root = dom.documentElement  
  
prefix = git + " clone http://android.googlesource.com/"  
suffix = ".git"  
  
if not os.path.exists(rootdir):  
    os.mkdir(rootdir)  
      
for node in root.getElementsByTagName("project"):  
    os.chdir(rootdir)  
    d = node.getAttribute("path")  
    last = d.rfind("/")  
    if last != -1:  
        d = rootdir + "/" + d[:last]  
        if not os.path.exists(d):  
            os.makedirs(d)  
        os.chdir(d)  
    cmd = prefix + node.getAttribute("name") + suffix  
    print cmd  
    call(cmd, shell=True)   
test@myhost /home/test/Android % ll
总用量 216
-rw-r--r-- 1 test users      2  3月  2 14:34 android_download_source_code_steps.txt
-rw-r--r-- 1 test users    879  3月  2 14:42 download_android_src.py
drwxr-xr-x 3 test users   4096  3月  2 14:38 manifest/
-rw-r--r-- 1 test users  35672  3月  1 14:25 python_files.png
drwxr-xr-x 3 test users   4096  3月  1 14:31 Python_Src/
-rw-r--r-- 1 test users 164603  3月  1 16:08 using_authentication.png
test@myhost /home/test/Android % chmod +x download_android_src.py
test@myhost /home/test/Android % ll
总用量 216
-rw-r--r-- 1 test users      2  3月  2 14:34 android_download_source_code_steps.txt
-rwxr-xr-x 1 test users    879  3月  2 14:42 download_android_src.py*
drwxr-xr-x 3 test users   4096  3月  2 14:38 manifest/
-rw-r--r-- 1 test users  35672  3月  1 14:25 python_files.png
drwxr-xr-x 3 test users   4096  3月  1 14:31 Python_Src/
-rw-r--r-- 1 test users 164603  3月  1 16:08 using_authentication.png
1 test@myhost /home/test/Android % python --version
Python 2.7.3
test@myhost /home/test/Android % ./download_android_src.py
git clone http://android.googlesource.com/platform/build.git
正克隆到 'build'...
remote: Sending approximately 23.92 MiB ...
remote: Counting objects: 963, done
remote: Finding sources: 100% (176/176)