【树莓派】为Ubuntu for ARM 更换中国软件源

更换步骤
以root身份打开 /etc/apt/sources.list ，至于用什么打开随意
将 http://ports.ubuntu.com/ 全部替换为 http://mirrors.ustc.edu.cn/ubuntu-ports/ ，这是中科大的
执行 sudo apt-get update 和 sudo apt-get upgrade 测试

查看是否提供arm支持的方法

打开一个镜像站点，然后以此打开 /dists/xenial/main/ ，看这个目录下面有没有 binary-arm 这样的字眼，如果有，就是提供arm支持的
上面部分来自https://blog.csdn.net/wr132/article/details/56700479
可参考该网址：https://mirror.tuna.tsinghua.edu.cn/help/raspbian/
https://zhuanlan.zhihu.com/p/35017671
下面贴出具体的代码：

## Note, this file is written by cloud-init on first boot of an instance
## modifications made here will not survive a re-bundle.
## if you wish to make changes you can:
## a.) add 'apt_preserve_sources_list: true' to /etc/cloud/cloud.cfg
##     or do the same in user-data
## b.) add sources in /etc/apt/sources.list.d
## c.) make changes to template file /etc/cloud/templates/sources.list.tmpl

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial main restricted
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial-updates main restricted
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial universe
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial universe
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial-updates universe
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial multiverse
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial-updates multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial-backports main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial-backports main restricted universe multiverse

deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial-security main restricted
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial-security main restricted
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial-security universe
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial-security universe
deb http://mirrors.ustc.edu.cn/ubuntu-ports xenial-security multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu-ports xenial-security multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu xenial partner
# deb-src http://archive.canonical.com/ubuntu xenial partner