I know it's possible to rotate video output in X server to display in portrait mode as well as landscape.
I'm curious if it's possible to rotate the video output that occurs pre-X server. The white text on black background output as the machine boots (rc.sysinit, bringing up eth connections, etc.).
if you use the framebuffer-console you can use the fbcon=rotate:n command at boot time to rotate the console output.
(n = 0: no rotation, n=1 90deg clockwise, n=2 upside down, n=3: 90deg counterclockwise)
The framebuffer options are documented in the kernel source in the file
linux-source-2.6.32/Documentation/fb/fbcon.txt