Configure Ubuntu12.04 to boot without a monitor

Normally, the Ubuntu 12.04 desktop system is for PC which is assumed to be connected with a monitor, a keyboard and a mouse. As I just want to remotely login to the computer, I just removed those devices and leave the machine with only power and network. Everything works fine before I need to reboot the machine remotely. Then I can never connected it again before I reconnect it with a monitor and reboot it.

To solve the problem, I finally find this post: http://ubuntuforums.org/showthread.php?t=1452600&page=3 . The solution is:

Step 1. Back up the original xorg.conf to xorg.conf.bk just in case. Create a new xorg.conf in /etc/X11 with the following. 

Section "Device"
Identifier "VNC Device"
Driver "vesa"
EndSection

Section "Screen"
Identifier "VNC Screen"
Device "VNC Device"
Monitor "VNC Monitor"
SubSection "Display"
Modes "1024x768"
EndSubSection
EndSection

Section "Monitor"
Identifier "VNC Monitor"
HorizSync 30-70
VertRefresh 50-75
EndSection

Step 2. Disable KMS for your video card

The list is to know which video card manufacturer you have and use the command line entry below it to create the appropriate kms.conf file with the line "options...modeset=0" line in it. If you have access to the GUI you could just are easily create/modify the file and put the "options...modeset=0" in as appropriate.

The following are input into the terminal windows as a line command.

# ATI Radeon:
echo options radeon modeset=0 > /etc/modprobe.d/radeon-kms.conf

# Intel:
echo options i915 modeset=0 > /etc/modprobe.d/i915-kms.conf

# Nvidia (this should revert you to using -nv or -vesa):
echo options nouveau modeset=0 > /etc/modprobe.d/nouveau-kms.conf

As for my case, mine is Intel, I add "option i915 modeset=0 " to /etc/modprobe.d/dkms.conf .

Step 3. Reboot