树莓派这些ubuntu18.04mate没法手动界面选（arm），就只能乖乖更改文件了。网上的大概都差不多，应该也都能用，我这里备份一份自己正常用的电脑上的sources.list

1. 备份sources.list

sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

最后的.backup只是改变文件的后缀不让起作用

2. vim修改sources.list

sudo vim /etc/apt/sources.list

输入i进入vim的插入模式，将里面的内容全部删除（只能键盘操作）

3. 复制
   x86电脑版本

# 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

树莓派等ARM版本使用ubuntu-ports 镜像

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

4. 将复制内容粘贴
   按下ctrl+shift+v就可以
5. 保存并退出
   先按一下Esc，然后输入:wq（注意是冒号+w+q），回车
6. 更新

sudo apt-get update

问题一：出现下面的

W: GPG 错误：http://mirrors.tuna.tsinghua.edu.cn/ros/ubuntu bionic Release: 由于没有公钥，无法验证下列签名： NO_PUBKEY F42ED6FBAB17C654
E: 仓库 “http://mirrors.tuna.tsinghua.edu.cn/ros/ubuntu bionic Release” 没有数字签名。
N: 无法安全地用该源进行更新，所以默认禁用该源。

解决办法：

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys F42ED6FBAB17C654