前言
最近在再重新安装Ubuntu18.04过程中，出现不少觉得对Ubuntu小白比较有用的问题解决方案，因此在此做出一些汇总，持续更新.....
apt安装软件包出现无法定位软件包
例如我的是无法定位软件包python-pip：
第一步，检查自己输入的包名是否错误，大小写也要注意。
第二步，更新。
$ sudo apt-get update
如果发现依然报错，执行第三步，替换源：
先备份
$ cd /etc/apt/
$ sudo cp sources.list sources.list.bb
$ sudo vi sources.list
替换为国内的源，一般选择阿里云的，清空sources.list，复制下面内容粘贴进去
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb 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 main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
之后
$ sudo apt update
$ sudo apt upgrade
大功告成！
