Disable Suspend mode on Raspberry Pi

The file /etc/lightdm/lightdm.conf is the configuration of LighDM, display manager. To disable Suspend mode, edit the file with the command:

$ sudo nano /etc/lightdm/lightdm.conf

Scroll down to [SeatDefaults] section, uncomment and edit the command "xserver-command=X" to enter X server command to run:
xserver-command=X -s 0 -dpms

/etc/lightdm/lightdm.conf

where:
-s 0 sets screen-saver timeout time in minutes.
-dpms disables DPMS (display power management services).

reference: http://www.xfree86.org/current/Xserver.1.html

Restart your Raspberry Pi.