遇到的问题：

E: 无法获得锁 /var/lib/dpkg/lock-frontend。锁正由进程 2973（unattended-upgr）持有
N: 请注意，直接移除锁文件不一定是合适的解决方案，且可能损坏您的系统。
E: 无法获取 dpkg 前端锁 (/var/lib/dpkg/lock-frontend)，是否有其他进程正占用它？

解决方案：

sudo rm /var/lib/dpkg/lock-frontend 

sudo rm /var/lib/dpkg/lock

遇到的问题：

源无法连接

解决方案：

更换源

（1）备份源文件：

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

（2）编辑新源文件

sudo rm -rf /etc/apt/sources.list
sudo nano /etc/apt/sources.list

在文件输入：

deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

(3)更新源文件

sudo apt-get update

发现需要安装QT环境

（1）去qt官网下载开源版安装包

网址：获取Qt —— 立即下载您可以借助Qt用一项技术和一套代码库在不同平台上创建、部署流畅、高性能、直观的UI、应用及嵌入式设备，从而最大限度地减少上市时间和减轻维护成本。Qt有两种许可证，请根据您的项目需求选择适合的版本。https://www.qt.io/zh-cn/download

（2）给安装包权限，否则可能无法打开安装包

chmod a+x qt-unified-linux-x64-4.2.0-online.run

（3）打开执行安装包

sudo ./qt-unified-linux-x64-4.2.0-online.run

（4）安装路径，我选择安装在/opt/QT

（5）安装的组件包/components，我选择的是5.15.2版本中的 Desktop gcc 64-bit 和 QT Charts

（6）打开用户目录并在.bashrc中写入

cd 

export PATH="/opt/Qt/Tools/QtCreator/bin:$PATH"
export PATH="/opt/Qt/5.15.2/gcc_64/bin:$PATH"
export LD_LIBRARY_PATH=/opt/Qt/5.15.2/gcc_64/lib:$LD_LIBRARY_PATH

（7）生效刚才编辑的bashrc

source ~/.bashrc

（8）运行

qmake -v

得到

QMake version 3.1
Using Qt version 5.15.2 in /opt/Qt/5.15.2/gcc_64/lib

遇到的问题

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.

Aborted (core dumped)

解决方案：

sudo apt-get install libxcb-xinerama0