Ubuntu CMake what path to add to CMAKE_MODULE_PATH

My OS is Ubuntu. I would like to change from QT4 to QT5 in my project. The native package though is 4.x version in Ubuntu right now.

I have downloaded the Linux installer from QT homepage and installed QT5.4 under /opt/Qt/5.4/

This path is not found by

find_package (Qt5 REQUIRED)

I tried adding

set(CMAKE_MODULE_PATH "/opt/QT/5.4;${CMAKE_MODULE_PATH}")

to my CMAKELIST.txt but that does not help.

Where do I have to link, or am I using the wrong syntax?

Some edits after hint with calling:

 cmake -DCMAKE_PREFIX_PATH=/opt/QT/5.4/gcc_64/ ../src/

I also have deleted the CMAKE_MODULE_PATH variable. I still get the same error:

 CMake Error at CMakeLists.txt:3 (find_package):
 Found package configuration file:
 /usr/lib/x86_64-linux-gnu/cmake/Qt5/Qt5Config.cmake
 but it set Qt5_FOUND to FALSE so package "Qt5" is considered to be NOT
 FOUND.  Reason given by package:

 The Qt5 package requires at least one component

I dont know why this is happening after reading https://blogs.kde.org/2008/12/12/how-get-cmake-find-what-you-want-it . There it is stated, that the path will be searched before the default search directories. The path I used seems to be right now:

/opt/QT/5.4/gcc_64/

Adding subfolder gcc_64 must be right, as this subfolder has "lib", "include" ect as subfolders.

I remeber that I have called also

sudo apt-get install QT5-default

some time ago. This did not help, I needed the installer from QT. Although I removed qt5-default again to prevent cmake from finding the wrong package configuration file, the same error appears.

See discussion below, moved to here: Cmake and QT5 - Include only takes one argument

You have to use the variable CMAKE_PREFIX_PATH, i.e. invoke

cmake -DCMAKE_PREFIX_PATH=/opt/QT/5.4 <path_to_source>

at the root of your build tree. Then you can use find_package(Qt5 ...) etc. See also the Qt5 cmake docs.

Rough distinction within you focus:

CMAKE_MODULE_PATH is for "general" inclusion of files and "FindXXX.cmake" files in find_package(... MODULE).
CMAKE_PREFIX_PATH has a special meaning in the context of find_package(... CONFIG).

After addition of new content

this is a new error and thus should require a new question. if you had that error before you'd have already found the Qt5 config.cmake file :-)

anyways, as the error tells you

The Qt5 package requires at least one component

you need to specify a component of the Qt5 package. As the cmake docs say, you need to use the find_package(Qt5 REQUIRED COMPONENTS Widgets Core ...) interface so that cmake (better: the logic of Qt5 FindQt5.cmake) knows what to look for. that will give you the targets Qt5::Widgets etc to use/link against. i dont know if the syntax find_package(Qt5Widgets REQUIRED) works, could be equivalent.