更改ubuntu19.04的镜像源

备份好  /etc/apt/sources.list文件后，将sources.list里面的内容修改为清华镜像源：

# 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/ disco main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-security main restricted universe multiverse

但执行sudo apt-get update时，仍是404或显示repository does not have a release file error

解决方案：

①若报错中显示不信任网站时，要在deb后面加[trusted=yes];

②disco的镜像源好像有问题，19.04的名字disco换成19.10的名字eoan，方法如下：

sudo sed -i -e 's|disco|eoan|g' /etc/apt/sources.list
sudo apt update

ps：好像使用18.04的源也可以：https://developer.aliyun.com/mirror/ubuntu?spm=a2c6h.13651102.0.0.3e221b11WO9omJ