I have both qt4 and qt5 on my Linux system. qt4 is used by default. What is a clean way to change that so that qmake uses qmake-qt5 by default?
The system might have different meta packages that handle the default.
For example on Debian there is a qt4-default and a qt5-default package, installing one of them will uninstall the other and set the symlinks appropriately
There is a tool named qtchooser to switch between Qt versions. On Debian and Ubuntu you can install it with apt-get install qtchooser.
Easiest way is to use it to list the alternatives and then create QT_SELECT environment variable.
$ qtchooser -list-versions
4
5
default
opt-qt55
qt4-i386-linux-gnu
qt4
qt5-i386-linux-gnu
qt5
Then you create QT_SELECT environment variable and set e.g. export QT_SELECT=4 or export QT_SELECT=5.
来源：https://stackoverflow.com/questions/39735998/make-qmake-use-qt5-by-default