1、获取当前系统版本的Codename

lsb_release -a | grep Codename | awk '{print $2}' # 输出结果为下文中的Codename

Ubuntu 12.04 (LTS)代号为precise。
Ubuntu 14.04 (LTS)代号为trusty。
Ubuntu 15.04 代号为vivid。
Ubuntu 15.10 代号为wily。
Ubuntu 16.04 (LTS)代号为xenial。
Ubuntu 18.04 (LTS)代号为bionic。
Ubuntu 20.04 (LTS)代号为focal。

2、备份原来的系统源

cd /etc/apt
sudo mv sources.list sources.list.bak

3、写入阿里云的源

vim /etc/apt/sources.list

下面源信息中$Codename为第一步中系统的Codename，批量替换即可。

deb http://mirrors.aliyun.com/ubuntu/ $Codename main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ $Codename-backports main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ $Codename-proposed main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ $Codename-security main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ $Codename-updates main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-backports main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-proposed main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-security main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-updates main multiverse restricted universe

4、执行更新

执行以下命令，完成更新。

apt-get update

5、一键更换源的脚本(参考)

以下脚本可以一键完成以上步骤：

#/bin/bash
#一键更换ubuntu apt源
##获取当前系统版本的Codename
CODENAME=$(lsb_release -c --short)

##备份原有源文件，以当前日期重命名
mv /etc/apt/sources.list /etc/apt/sources.list.$(date +%Y_%m_%d_%H:%M).back

##写入模板文件
cat > /etc/apt/sources.list <<EOF
deb http://mirrors.aliyun.com/ubuntu/ CODENAME main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ CODENAME-backports main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ CODENAME-proposed main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ CODENAME-security main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ CODENAME-updates main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ CODENAME main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ CODENAME-backports main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ CODENAME-proposed main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ CODENAME-security main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ CODENAME-updates main multiverse restricted universe
EOF

##替换Codename
sed -i 's/CODENAME/${CODENAME}/g' /etc/apt/sources.list

##更新apt源
apt-get update