使用ARM架构的Ubuntu源，在官方说明（https://mirrors.tuna.tsinghua.edu.cn/help/ubuntu/ ）中选择了18.04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

在此页最下面的链接，指向了（https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/）

看地址可知：Ubuntu x86架构的，地址是：

`https://mirrors.tuna.tsinghua.edu.cn/**ubuntu/**`

而说明上树莓派的地址是：

`https://mirrors.tuna.tsinghua.edu.cn/**ubuntu-ports/**`

因此，将最开始的Ubuntu x86源地址中的ubuntu 改为：ubuntu-ports，即得到：

# 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-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-port**s/ 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

# 预发布软件源，不建议启用

# deb https://mirrors.tuna.tsinghua.edu.cn/**ubuntu-ports**/ bionic-proposed main restricted universe multiverse

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