在此之前你可以备份一下，以及时恢复
mv /etc/apt/sources.list /etc/apt/sources.list.bak;

你可以使用命令sudo apt edit-sources编辑源或在 /etc/apt/sources.list 中增加下面其中一些源
修改后使用sudo apt update更新缓存，sudo apt upgrade升级包。如果有报错的及时删除后再更新就行了

#清华大学开源软件镜像站

# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释

deb
https://mirrors.tuna.tsinghua… bionic main restricted universe multiverse

# deb-src
https://mirrors.tuna.tsinghua… bionic main restricted universe multiverse

deb
https://mirrors.tuna.tsinghua… bionic-updates main restricted universe multiverse

# deb-src
https://mirrors.tuna.tsinghua… bionic-updates main restricted universe multiverse

deb
https://mirrors.tuna.tsinghua… bionic-backports main restricted universe multiverse

# deb-src
https://mirrors.tuna.tsinghua… bionic-backports main restricted universe multiverse

deb
https://mirrors.tuna.tsinghua… bionic-security main restricted universe multiverse

# deb-src
https://mirrors.tuna.tsinghua… bionic-security main restricted universe multiverse

# 预发布软件源，不建议启用

# deb
https://mirrors.tuna.tsinghua… bionic-proposed main restricted universe multiverse

# deb-src
https://mirrors.tuna.tsinghua… bionic-proposed main restricted universe multiverse

# 阿里云
deb http://mirrors.aliyun.com/ubu… trusty main restricted universe multiverse
deb http://mirrors.aliyun.com/ubu… trusty-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubu… trusty-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubu… trusty-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubu… trusty-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubu… trusty main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubu… trusty-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubu… trusty-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubu… trusty-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubu… trusty-backports main restricted universe multiverse

# 中科大源
deb https://mirrors.ustc.edu.cn/u… bionic main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/u… bionic main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/u… bionic-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/u… bionic-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/u… bionic-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/u… bionic-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/u… bionic-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/u… bionic-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/u… bionic-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/u… bionic-proposed main restricted universe multiverse

# 网易163
deb http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse

# Ubuntu 官方源
deb http://archive.ubuntu.com/ubu… gutsy main restricted universe multiverse
deb http://archive.ubuntu.com/ubu… gutsy-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubu… gutsy-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubu… gutsy-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubu… gutsy-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubu… gutsy main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubu… gutsy-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubu… gutsy-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubu… gutsy-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubu… gutsy-backports main restricted universe multivers