Read the statement by Michael Teeuw here.
Rotate screen problem when MM starts
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 @sdetweil thx for your fast answer 
 release isNo LSB modules are available. 
 Distributor ID: Raspbian
 Description: Raspbian GNU/Linux 11 (bullseye)
 Release: 11
 Codename: bullseyeimage below is my orientation screen. how i turn the black slash screen ? ![alt text]https://ibb.co/bK1s7Gc(image url) 
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 @MisterT u have to edit the image and rotate it 
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 @sdetweil if i turn on left right or inverted, when i start MM screen rotate on normal position 
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 @MisterT makes no sense. do 
 pm2 stop all
 pm2 delete 0
 pm2 savethen boot to rotated 
 pm2 start installers/pm2_MagicMirror.json
 should be vertical
 then ctrl-m
 pm2 savethen sudo reboot 
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 @sdetweil thx for your support. i found the guilty module after 2 hours. it’s MMM-PIR-Sensor-Lite. There is an hidden rotate parameter and the default parameter is normal rotate. that’s why when MM starts there was a rotate screen on normal position. So for people with rotate problem when MM Starts and if you have MMM-PIR-Sensor-Lite, add this parameter in your config.js: rotation Direction of content rotation. Possible values: ‘normal’, ‘left’, ‘right’ or ‘inverted’ 
 Default value: ‘normal’
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 @MisterT ah, the xrandr under the covers… glad u found it. thanks for the feedback 
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 I don’t know about the Pi3, but on the Pi4 you just go to display settings and tell it to go vertical… easier than all this programming that I never got to work with my MM 
