执行repo sync 的时候，错误信息：error: Exited sync due to gc errors
原因： repo 升级，不兼容GIT 1.7.2 以下的版本。
方案升级git到 1.7.2以及以上的版本。
Ubuntu10.x用户可尝试如下操作：
1 修改/etc/apt/sources.list文件
把下面内容加到最后面
deb http://mirrors.163.com/ubuntu/ oneiric main universe restricted multiverse
deb-src http://mirrors.163.com/ubuntu/ oneiric main universe restricted multiverse
deb http://mirrors.163.com/ubuntu/ oneiric-security universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-security universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ oneiric-updates universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ oneiric-proposed universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-proposed universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ oneiric-backports universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-backports universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-updates universe main multiverse restricted
2 执行下面两个命令
sudo apt-get update
sudo apt-get install git