Can not quit full screen mode in glut

I wrote a glut program in linux, which has glut 3.7 instralled.

First I use “glutFullScreen” to enter full screen mode. It’s OK, I got full screen. But after that, I can not quit full screen by “glutPositionWindow” and “glutReshapeWindow”. In the online menu of glut, the full screen mode should be quit by these two functions.

I also tested my code in my windows platform, which has glut 3.6 installed. In such situation, I can quit full screen mode successfully.

Is anybody has any idea about that?