からhttps://www.cnblogs.com/gabin/p/6519352.html
私のシステムは16.04 LTSです.

バックアップ

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

新規作成

sudo vim/etc/apt/sources.list
ファイルの内容:

deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
## 
deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
#  
deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
## 
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
# Canonical  
deb http://archive.canonical.com/ubuntu/ xenial partner
deb http://extras.ubuntu.com/ubuntu/ xenial main

更新

sudo apt-get update
sudo apt-get upgrade