Ygtjki

I have a ubuntu 14.04 server that connects to a A/V Amplifier via HDMI.

The problem is, if the amp has a source selected other than the Ubuntu during boot up of the ubuntu m/c, then when the ubu server source is selected there is no output.

This is the output of xrandr when the m/c IS selected as the A/V source during bootup:

xrandr -d :0
Screen 0: minimum 320 x 200, current 1600 x 1200, maximum 16384 x 16384
DFP1 disconnected (normal left inverted right x axis y axis)
DFP2 disconnected (normal left inverted right x axis y axis)
DFP3 disconnected (normal left inverted right x axis y axis)
DFP4 disconnected (normal left inverted right x axis y axis)
DFP5 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 160mm x 90mm
 1920x1080 60.0*+ 50.0 59.9 60.1 50.0 30.0 25.0 24.0 60.0 30.0 24.0 
 1776x1000 50.0 59.9 50.0 25.0 24.0 60.0 30.0 

DFP6 disconnected (normal left inverted right x axis y axis)
CRT1 disconnected (normal left inverted right x axis y axis)

I have tried executing a xrandr script with CRON during boot, however that does not work:

@reboot /usr/bin/xrandr -d :0 --addmode DFP5 1920x1080; /usr/bin/xrandr -d :0 --output DFP5 --mode 1920x1080;

I also tried modifying the kernel params in /etc/default/grub.conf:

GRUB_CMDLINE_LINUX_DEFAULT="video=HDMI-A-1:1920x1080D"
GRUB_CMDLINE_LINUX_DEFAULT="video=HDMI-A:1920x1080D"

I tried both HDMI-A and HDMI-A-1 as I see that others have used that ID, but neither work.

After rebooting with the server NOT selected as the A/V source, and running xrandr it appears that CRT is enabled, but not the HDMI Source:

# xrandr -d :0
Screen 0: minimum 320 x 200, current 1600 x 1200, maximum 16384 x 16384
DFP1 disconnected (normal left inverted right x axis y axis)
DFP2 disconnected (normal left inverted right x axis y axis)
DFP3 disconnected (normal left inverted right x axis y axis)
DFP4 disconnected (normal left inverted right x axis y axis)
DFP5 disconnected (normal left inverted right x axis y axis)
DFP6 disconnected (normal left inverted right x axis y axis)
CRT1 connected 1600x1200+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
 1600x1200 60.0*+
 1400x1050 60.0 

How can I force the HDMI to be enabled and connected during boot, irregardless of whether or not it detects a monitor ?

This sounds very similar to an issue I had with my monitor connected via HDMI to an NVIDIA GPU running 14.04. The GPU would not boot if the monitor was disconnected. If the monitor is connected, then everything boots fine. We ended up changing a setting that allowed for an empty configuration and it worked fine.

Here is the solution we used:

https://devtalk.nvidia.com/default/topic/793405/embedded-systems/tegra-k1-hdmi-boot-into-desktop-ubuntu/post/4382630/#4382630

Hopefully, this works for you as well. Good luck!

I had a similar problem recently and solved it by adding this
to /etc/default/grub (note the ':' in front of the 'D'):

GRUB_CMDLINE_LINUX_DEFAULT="video=HDMI-A-1:1920x1080@60:D"

and reloading the grub config:

sudo update-grub

More info can be found at https://wiki.archlinux.org/index.php/Kernel_mode_setting

I had the same problem with my Debian 9 install;

 service lightdm restart 

did the trick for me.