http://developer.android.com/sdk/index.html
http://source.android.com/source/
1.curl https://dl-ssl.google.com/dl/googlesource/git-repo/repo > ~/bin/repo
执行curl https://dl-ssl.google.com/dl/googlesource/git-repo/repo > ~/bin/repo会出现如下错误：
root@ubuntu:~ curl https://dl-ssl.google.com/dl/googlesource/git-repo/repo > ~/bin/repo
--2013-04-21 04:30:42-- https://dl-ssl.google.com/dl/googlesource/git-repo/repo
Resolving dl-ssl.google.com... 74.125.128.91, 74.125.128.93, 74.125.128.136, ...
Connecting to dl-ssl.google.com|74.125.128.91|:443... failed: Connection refused.
Connecting to dl-ssl.google.com|74.125.128.93|:443... failed: Connection timed out.
Connecting to dl-ssl.google.com|74.125.128.136|:443... failed: Connection timed out.
Connecting to dl-ssl.google.com|74.125.128.190|:443... failed: Connection timed out.
Connecting to dl-ssl.google.com|2404:6800:4005:c00::5d|:443... failed: Network is unreachable.
2.在执行repo sync下载android的时候出现如下信息：
error: Failed to connect to 2404:6800:4008:c00::52: Network is unreachable while accessinghttps://android.googlesource.com/platform/manifest/info/refs?service=git-upload-pack
fatal: HTTP request failed
error: Failed to connect to 2404:6800:4008:c00::52: Network is unreachable while accessinghttps://android.googlesource.com/platform/manifest/info/refs?service=git-upload-pack
fatal: HTTP request failed
curl: (7) Failed to connect to 2404:6800:4008:c00::52: Network is unreachable
curl: (7) Failed to connect to 2404:6800:4008:c00::52: Network is unreachable
curl: (7) Failed to connect to 2404:6800:4008:c00::52: Network is unreachable
curl: (7) Failed to connect to 2404:6800:4008:c00::52: Network is unreachable
error: Failed to connect to 2404:6800:4008:c00::52: Network is unreachable while accessinghttps://android.googlesource.com/platform/bootable/bootloader/legacy/info/refs?service=git-upload-pack
fatal: HTTP request failed
error: Failed to connect to 2404:6800:4008:c00::52: Network is unreachable while accessinghttps://android.googlesource.com/platform/bootable/recovery/info/refs?service=git-upload-pack
fatal: HTTP request failed
解决方法
1. 浏览器登录https://android.googlesource.com/new-password，并用gmail帐号登录（去谷歌注册）；
2. 点击网页上的“允许访问”，得到类似
1 machine android.googlesource.com login git-<userName>.gmail.com password <password> 2 machine android-review.googlesource.com login git-<userName>.gmail.com
password <password>
3. 把上面那段信息追加到~/.netrc文件结尾(请检查当前用户的权限, 如果不存在此文件则自己新建一个)；
4. 下载地址的URI更改为https://android.googlesource.com/a/platform/manifest（中间加上了“/a”）。
5. repo init -u https://android.googlesource.com/a/platform/manifest -b android-2.3.3_r1
6. repo sync
即可拉下Android源码。
官方的说法是：因为访问基本是匿名的，为了防止连接过多(指内网/虚拟机)，对同一IP地址的连接数做了一定的限制。看来是用gmail帐号进行认证。
这样的话，在公司网络内或者用虚拟机下载的话，会经常遇到这问题。
源码官网指导网址:http://source.android.com/source/downloading.html