LSB Version:	core-11.1.0ubuntu2-noarch:security-11.1.0ubuntu2-noarch
Distributor ID:	Ubuntu
Description:	Ubuntu 20.10
Release:	20.10
Codename:	groovy

按照https://www.openfoam.com/download/openfoam-installation-from-source的步骤来安装，首先需要按照https://www.openfoam.com/documentation/system-requirements安装一些系统软件，第一部分如下：

sudo apt-get update
sudo apt-get install build-essential flex bison cmake zlib1g-dev libboost-system-dev libboost-thread-dev libopenmpi-dev openmpi-bin gnuplot libreadline-dev libncurses-dev libxt-dev
sudo apt-get install qt4-dev-tools libqt4-dev libqt4-opengl-dev freeglut3-dev libqtwebkit-dev

执行第三行命令时出现错误：

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package libqt4-dev is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Unable to locate package qt4-dev-tools
E: Package 'libqt4-dev' has no installation candidate
E: Unable to locate package libqt4-opengl-dev
E: Unable to locate package libqtwebkit-dev

网上的说法是要换国内的源，所以按照https://blog.csdn.net/qq_42824983/article/details/110236257更换为阿里源，但是问题仍然存在，而且sudo apt-get upgrade后还有三百多个not upgraded，于是来论坛请教。
还有个小问题，刚才那个教程里的get-apt update以及apt-get upgrade无法被执行，在前面加sudo就行了，不知道是作者漏写了还是其它原因？
感谢各位老师和前辈！