一、前言
今天使用apt install build-essential 時出現了以下錯誤，想想dpkg-dev，這個包管理器，應該是系統自帶的包管理工具吧，怎麼可能不滿足。所以對網絡進行了地毯式的搜索，終於發現了問題。
二、出現原因
原因在於 /etc/apt/source.list 文件，因爲國外源網速慢，所以之前配置了apt國內源，當時是隨便找了一個源就寫進去了，這就埋下了病根，源頭就是這裏，我添加了不符合我的ubuntu版本的國內阿里雲的軟件源。所以
三、我的解決方案
上網搜索符合自己Ubuntu版本的國內源，然後替換已經寫入文件的其他版本的國內源。於是搞定了。如果沒有搞定，請務灰心，總會解決的。
四、附
1、查看自己的系統版本
cat /proc/version
如下圖是我的版本，於是就去搜索版本號加國內源，就會出現一大堆。
2、apt update的暗示
3、阿里源
trusty
deb http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
focal
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security multiverse
bionic
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/ bionicupdates 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 rstricted universe multiverse
4、版本代號分佈
參考自 博客
（https://blog.csdn.net/jhsword/article/details/96853061）
