1.事件背景

　　事情起因是因为我想安装xvfb，执行sudo apt-get install xvfb发现安装报错，看报错原因是被墙导致，因为我用的默认源也没有挂代理；然后就百度，发现都是互相抄，什么换阿里源啊，163源、中科源之类，我都试过，并且发现这些源在更新过程会有一些错误或者更新被忽略，导致我再次执行sudo apt-get install -y xvfb报错说未找到包。

　　我就接着百度，然后有一条评论给了我灵感，既然默认源切换国区可以安装包，那么我把默认域名us.ports.ubuntu.com换成国内的，us代表美国，zh代表中国，我就试了zh.ports.ubuntu.com，发现真的可以！

2. 替换方法

Ps：我使用的系统是Ubuntu 18.04 LTS

1.先对默认源进行备份

sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak

2.进入默认源编辑

sudo vi /etc/apt/sources.list

3.全局替换

 3.1 按ESC键输入:
 3.2 粘贴下面批量替换命令

%s/us\./zh\./g

4. 保存后再执行更新源命令

执行完上述操作步骤后再输入你想安装的包，会发现可以安装了！

最后我想吐槽那些原封不动的抄袭者，虽然转载他人文章可以备份，但是当某一天你想上网查找一个问题的解决方法时，发现全网都是同一个答案，还是一模一样的，而想要找到真正有用的答案无异于海底捞针！

3. 完整源文件备份

默认源文件

#

# deb cdrom:[Ubuntu-Server 18.04.3 LTS _Bionic Beaver_ - Release arm64 (20190805)]/ bionic main restricted

#deb cdrom:[Ubuntu-Server 18.04.3 LTS _Bionic Beaver_ - Release arm64 (20190805)]/ bionic main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.ports.ubuntu.com/ubuntu-ports/ bionic main restricted
# deb-src http://us.ports.ubuntu.com/ubuntu-ports/ bionic main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.ports.ubuntu.com/ubuntu-ports/ bionic-updates main restricted
# deb-src http://us.ports.ubuntu.com/ubuntu-ports/ bionic-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://us.ports.ubuntu.com/ubuntu-ports/ bionic universe
# deb-src http://us.ports.ubuntu.com/ubuntu-ports/ bionic universe
deb http://us.ports.ubuntu.com/ubuntu-ports/ bionic-updates universe
# deb-src http://us.ports.ubuntu.com/ubuntu-ports/ bionic-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://us.ports.ubuntu.com/ubuntu-ports/ bionic multiverse
# deb-src http://us.ports.ubuntu.com/ubuntu-ports/ bionic multiverse
deb http://us.ports.ubuntu.com/ubuntu-ports/ bionic-updates multiverse
# deb-src http://us.ports.ubuntu.com/ubuntu-ports/ bionic-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://us.ports.ubuntu.com/ubuntu-ports/ bionic-backports main restricted universe multiverse
# deb-src http://us.ports.ubuntu.com/ubuntu-ports/ bionic-backports main restricted universe 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 bionic partner
# deb-src http://archive.canonical.com/ubuntu bionic partner

deb http://ports.ubuntu.com/ubuntu-ports bionic-security main restricted
# deb-src http://ports.ubuntu.com/ubuntu-ports bionic-security main restricted
deb http://ports.ubuntu.com/ubuntu-ports bionic-security universe
# deb-src http://ports.ubuntu.com/ubuntu-ports bionic-security universe
deb http://ports.ubuntu.com/ubuntu-ports bionic-security multiverse
# deb-src http://ports.ubuntu.com/ubuntu-ports bionic-security multiverse

修改后国内可用源文件

# 

# deb cdrom:[Ubuntu-Server 18.04.3 LTS _Bionic Beaver_ - Release arm64 (20190805)]/ bionic main restricted

#deb cdrom:[Ubuntu-Server 18.04.3 LTS _Bionic Beaver_ - Release arm64 (20190805)]/ bionic main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://zh.ports.ubuntu.com/ubuntu-ports/ bionic main restricted
# deb-src http://zh.ports.ubuntu.com/ubuntu-ports/ bionic main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://zh.ports.ubuntu.com/ubuntu-ports/ bionic-updates main restricted
# deb-src http://zh.ports.ubuntu.com/ubuntu-ports/ bionic-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://zh.ports.ubuntu.com/ubuntu-ports/ bionic universe
# deb-src http://zh.ports.ubuntu.com/ubuntu-ports/ bionic universe
deb http://zh.ports.ubuntu.com/ubuntu-ports/ bionic-updates universe
# deb-src http://zh.ports.ubuntu.com/ubuntu-ports/ bionic-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://zh.ports.ubuntu.com/ubuntu-ports/ bionic multiverse
# deb-src http://zh.ports.ubuntu.com/ubuntu-ports/ bionic multiverse
deb http://zh.ports.ubuntu.com/ubuntu-ports/ bionic-updates multiverse
# deb-src http://zh.ports.ubuntu.com/ubuntu-ports/ bionic-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://zh.ports.ubuntu.com/ubuntu-ports/ bionic-backports main restricted universe multiverse
    
# deb-src http://zh.ports.ubuntu.com/ubuntu-ports/ bionic-backports main restricted universe 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 bionic partner
# deb-src http://archive.canonical.com/ubuntu bionic partner

deb http://ports.ubuntu.com/ubuntu-ports bionic-security main restricted
# deb-src http://ports.ubuntu.com/ubuntu-ports bionic-security main restricted
deb http://ports.ubuntu.com/ubuntu-ports bionic-security universe
# deb-src http://ports.ubuntu.com/ubuntu-ports bionic-security universe
deb http://ports.ubuntu.com/ubuntu-ports bionic-security multiverse
# deb-src http://ports.ubuntu.com/ubuntu-ports bionic-security multiverse