我们用ubuntu更新系统时会发现更新速度非常慢，这是因为ubuntu默认源是国外的，这就导致了更新非常慢。而我们只需要把源改成国内源，这时速度就会快很多。
一、命令行界面
1、备份原来的源文件
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2、编辑源文件
sudo nano /etc/apt/sources.list
3、注释掉原来的国外源（或者清空文件），并将中国国内源复制到文件中
4、执行更新
sudo apt update
最后推荐几个国内源
1、清华大学源
地址：https://mirror.tuna.tsinghua.edu.cn/help/ubuntu/
18.04 LTS
# 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.edu.cn/ubuntu/ bionic main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
# 预发布软件源，不建议启用
# deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
2、阿里源18.04LTS
地址：https://developer.aliyun.com/mirror/ubuntu?spm=a2c6h.13651102.0.0.3e221b11rTZb1T
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src 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-backports main restricted universe multiverse
3、腾讯源16.04LTS
地址：https://mirrors.cloud.tencent.com/help/ubuntu.html
Ubuntu 16.04
deb http://mirrors.cloud.tencent.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.cloud.tencent.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.cloud.tencent.com/ubuntu/ xenial-updates main restricted universe multiverse
#deb http://mirrors.cloud.tencent.com/ubuntu/ xenial-proposed main restricted universe multiverse
#deb http://mirrors.cloud.tencent.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.cloud.tencent.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.cloud.tencent.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.cloud.tencent.com/ubuntu/ xenial-updates main restricted universe multiverse
#deb-src http://mirrors.cloud.tencent.com/ubuntu/ xenial-proposed main restricted universe multiverse
#deb-src http://mirrors.cloud.tencent.com/ubuntu/ xenial-backports main restricted universe multiverse
