Raspberry Pi boot and work perfectly as server with Rainbow screen

Question

I searched for an hour and every problem about the rainbow screen is related to a boot problem. Not for me, I have no boot problem!

In my case, my raspberry pi 2 is working perfectly as a server, allowing ssh login within a minute after being powered, runs httpd and other services perfectly fine. I even have the console size in dmesg:

$ dmesg | grep Console
[    0.000000] Console: colour dummy device 80x30
[   11.370802] Console: switching to colour frame buffer device 53x21
$ dmesg | grep fb1
[   11.380644] graphics fb1: flexfb frame buffer, 320x240, 150 KiB video memory, 4 KiB DMA buffer memory, fps=20, spi0.0 at 48 MHz
$ uname -a
Linux raspberrypi 3.12.21+ #1 PREEMPT Sat Jun 14 12:01:42 CEST 2014 armv6l GNU/Linux
$ cat /etc/issue
Raspbian GNU/Linux 7 \n \l

The only problem is that HDMI consistently only output a rainbow screen at full-screen size, while the intended purpose of the Pi is to serve as an X Terminal.

I've tried 3 different power supplies both advertised more than 2.5A and 3 different cables and 2 different monitors, as well as the boot_delay=1 option. Now it is a network box, with no capacity to display.

Answer 1

As I dig through documents I realised there are 2 display devices: /dev/fb0 and /dev/fb1.

The Raspberry Pi was plugged to HDMI (/dev/fb0), which shows the Rainbow screen, but proper boot message is shown on the TFT (/dev/fb1), which remained unplugged. Once I plug the TFT on it I can see the boot process and console login.

I wasted a lot of time because I believe Linux would output the console and boot message to /dev/fb0 (HDMI, 1920×1080) while it actually goes to /dev/fb1 (TFT, 320×240).