修改Ubuntu默认apt下载源
默认下载源很慢，改成阿里的下载速度超快
sudo vim /etc/apt/sources.list
将文件内容替换成
deb https://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
更新
sudo apt-get update
sudo apt-get upgrade默认下载源很慢，改成阿里的下载速度超快
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