My system has two monitors so the main one is in the middle (or right) and the secondary one on the left.
The problem is that Linux always seems to take the left one to be the main one. The taskbar and menu are in it and the windows also open on it, including the login screen.
There is some way to put the middle / right to be the main one, because when I do not need to use the two I keep the one on the left off.
I am using the proprietary ATI drivers in Linux Mint 17.
At first glance it may seem like a trivial problem, however whenever you changed the layout of monitors by Catalyst the monitor on the left was set to primary. You will get the login screen and the taskbar.
Mint also seems to always pick up the leftmost monitor as a primary.
After much searching for similar problems, in this link the command
xrandr --output CRT1 --primary --auto --pos 0x0 --output LVDS --auto --left-of CRT1
But every time you reboot the system or adjust the resolution, everything would stay on the leftmost monitor.
I edited the /etc/X11/xorg.conf file and left it as follows in this link
Section "Device"
Identifier "amdcccle-Device[1]-0"
Driver "fglrx"
Option "Monitor-LVDS" "0-LVDS"
Option "Monitor-CRT1" "0-CRT1"
BusID "PCI:1:0:0"
EndSection
But it did not work.
Just the hint in this link was that I was able to solve the problem.
I edited the /etc/X11/xorg.conf file and inserted the following
Section "Monitor"
...
Option "Primary" "true"
EndSection