sudo nano /boot/config.txt
display_rotate=0 Normal
display_rotate=1 90 degrees
display_rotate=2 180 degrees
display_rotate=3 270 degrees
display_rotate=0x10000 horizontal flip
display_rotate=0x20000 vertical flip
Note: the 90 and 270 degrees rotation options require additional memory on GPU, so won't work with the 16M GPU split.
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