Change desktop orientation permanently for Debian

1. Connect beagle bone with serial cable.

2. login with root.

3. Type following command

beaglebone login: root

root@beaglebone:~# cd /

root@beaglebone:/#

root@beaglebone:/# find -name xorg.conf

root@beaglebone:/# nano ./etc/X11/xorg.conf

First section  lists all the available monitors in the system and second section is related to Monitor device settings.
Pay attention to "Option" tag. You can specify "Rotate" command with direction "CW".
Remove Option Tag if you don't want to specify rotation.

root@beaglebone:/# reboot