一、更換/etc/apt/sources.list文件裏的源
1. 備份源列表
Ubuntu配置的默認源並不是國內的服務器，下載更新軟件都比較慢。首先備份源列表文件sources.list：
# 首先備份源列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup
2. 打開sources.list文件修改
選擇合適的源，替換原文件的內容，保存編輯好的文件, 以阿里雲更新服務器爲例（可以分別測試阿里雲、清華、中科大、163源的速度，選擇最快的）：
# 打開sources.list文件
sudo gedit /etc/apt/sources.list
編輯/etc/apt/sources.list文件, 在文件最前面添加阿里雲鏡像源：
# 阿里源
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
3. 刷新列表
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install build-essential
下載速度瞬間就起飛了。
參考：https://zhuanlan.zhihu.com/p/61228593