升級Ubuntu系統時遇到的這個問題， 原因是默認的源不是國內的，而且還可能導致下載慢等問題。
1.備份源
cd /etc/apt/
sudo cp sources.list sources.list.bat
2.更換源
sudo vim sources.list
清除sources.list內的所有內容.更換為
#阿里雲 Ubuntu 18.04
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
按“ [Shift] +ZZ ”保存並退出
3.刷新
apt-get update
apt-get upgrade
OK 啦 ！
溫馨提示：
更新系統后要換新的源->hugboy源庫