how do I read and write the framebuffer screen without errors?

I get this:

Code:

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root@Z00A:/ # cat /dev/urandom > /dev/graphics/fb0                       
tmp-mksh: cat: <stdout>: No space left on device

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or with direct access

Code:

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root@Z00A:/ # ln -n /dev/graphics/fb0 /dev/fb0
root@Z00A:/ # cat /dev/urandom > /dev/fb0                                     
tmp-mksh: cat: <stdout>: No space left on device

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How do I do it?