Detailed tutorial on installing qt5.12.8 and environment configuration on ubuntu18.04

After the installation is complete, you can find Qt Creator in your application.

Configuring environment variables

You need to configure the environment variables before you can use the qmake command directly
In Ubuntu, for all users, edit the /etc/profile file

sudo vim /etc/profile

Add at the end (Note: the path here corresponds to the installation path, please check whether yours corresponds)

export PATH="/opt/Qt5.12.8/Tools/QtCreator/bin:$PATH"
export PATH="/opt/Qt5.12.8/5.12.8/gcc_64:$PATH"

After the modification is complete, restart the system or use "source /etc/profile" or ". /etc/profile" to make the modification take effect. The source command is also called the "dot command", which is a dot symbol (.). The source command is usually used to re-execute the initialization file that has just been modified to make it take effect immediately without having to log out and log in again.

Enter qtcreator in the terminal to open Qt Creator directly

qtcreator

3. QT project test

Let's create a new Qt project to test it
File>>New File or Project, select Qt Widgets Application. For testing purposes, you can basically click Next all the way, and you can delete the project later.

The built test project

Add a textBrowser control to mainwindow.ui and write a standard greeting

Run >>>>>>>>>>>>>>>>> Error... As the saying goes, "A journey of a hundred steps begins with the halfway point", it has come to this point, hurry up and find a way to solve it

Found the reason

By default, Qt searches for dynamic link libraries in the /usr/lib/ directory, but many Linux distributions place OpenGL link libraries in other directories. For example, I use CentOS 7, and the OpenGL link library is located in the /usr/lib64/ directory, while for Ubuntu, the OpenGL link library is located in the /usr/lib/i386-linux-gnu/mesa/ directory. As long as we copy libGL.so to the /usr/lib/ directory, or create a link for libGL.so in the /usr/lib/ directory, the problem can be solved. Obviously the second method is better.
In addition, the OpenGL link library that comes with the Linux distribution has a version number added to the suffix, such as libGL.so.1, libGL.so.1.2.0, libGL.so.1.3.1, etc., but the OpenGL link library that Qt looks for during the linking phase does not have a version number.

In summary, we need Create a link for the OpenGL library in the /usr/lib/ directory and remove the version number.

If you don't know the specific path of libGL.so in the current Linux system, you can use the locate libGL command or find /usr -name libGL* command to find it, and then use ln -s to create a link. Follow the method:
#Find the location of libGL

# locate libGL
/usr/lib/x86_64-linux-gnu/libGL.so.1
/usr/lib/x86_64-linux-gnu/libGL.so.1.0.0
/usr/lib/x86_64-linux-gnu/libGLESv2.so.2
/usr/lib/x86_64-linux-gnu/libGLESv2.so.2.0.0
......

#Create a link. There may be multiple versions of libGL.so in the Linux system. Just create a link for any version. Ordinary users do not have permission to create links. Use the root user or sudo command.

#sudo ln -s /usr/lib/x86_64-linux-gnu/libGL.so.1 /usr/lib/libGL.so

Run again>>>>>>>>>>>>>>> Success

Summarize

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sudo chmod a+x qt-opensource-linux-x64-5.12.8.run

./qt-opensource-linux-x64-5.12.8.run