fullscreen with glut

I’m using GLUT under Linux. I want to be in a fullscreen mode and so I try to use the glutEnterGameMode function.
Yet, though I have initialized the mode with glutGameModeString function (800x600), the application opens the fullscreen mode but the resolution and the refresh rate don’t change (it’s still the desktop ones: 1024x768)

I have tried this with SDL and it works perfectly.

What is the problem with GLUT. And, as the purpose is to make a game, do you advise me to use SDL instead of SDL ?

Finally, it’s said that glutSwapBuffers waits for the vertical retrace but my scrolling is very jerky and I’m convinced that GLUT doesn’t do it.

Jonathan (Dukenuke)