archlinux / gdm - execute commands at initialization

In order to execute commands at the beginning of the X user session - before the window manager is started -  the xprofile file can be used. The xprofile file is similar in style to xinitrc.

Firstly, create the file ~/.xprofile if it does not exist already. Then, simply add the commands for the programs you wish to start with the session.

References:
- https://wiki.archlinux.org/index.php/xprofile