Setting positions of Messgae boxes

(1) How to set the position of message boxes on the screen. ?
By default on windows, message boxes are getting displayed in the centre, but on linux, they are getting displayed on random locations(mostly at the corners of the window).

(2) Also how to make QMessageBox modal.
On windows, they are modal by defaylt but not on linux machine thru one login they are modal & thru other login they are non-modal.

Thanks

How do you show the message box? Did you pass a parent?

yes i tried setting the parent, now its working fine. Thanks