NICE DCV post-installation check error xhost: unable to open display "0"

Question

I am trying to install NICE DCV server on EC2 Ubuntu 22.04.

I am running pos-installation check part from the Administrator guide, however when running command:
` sudo DISPLAY=:0 XAUTHORITY=$(ps aux | grep "X.*\-auth" | grep -v grep | sed -n 's/.*-auth $[^ ]\+$.*/\1/p') xhost | grep "SI:localuser:dcv$"`

I get `xhost:  unable to open display ":0"`

Unsure what went wrong, as I made sure to follow the all the steps from the pre-installation and installation sections. Any advice would be of much help, as this is first time that I am trying to install DCV.

Answer

Can you check your X server is running with
    
>   ps -ef | grep X

If it is not running then you can check the Xorg.0.log.

If you have a GPU you can check if the driver is working well with
    
>  nvidia-smi

Answer

Seems this is the error that pops up in the log files:

```
   230.917] (**) DUMMY(0):  Default mode "320x175": 15.8 MHz, 37.9 kHz, 85.3 Hz (D)
[   230.917] (II) DUMMY(0): Modeline "320x175"x85.3   15.75  320 336 368 416  175 191 192 222 doublescan +hsync -vsync (37.9 kHz d)
[   230.917] (==) DUMMY(0): DPI set to (96, 96)
[   230.917] (II) Loading sub module "fb"
[   230.917] (II) LoadModule: "fb"
[   230.917] (II) Module "fb" already built-in
[   230.917] (II) Loading sub module "ramdac"
[   230.917] (II) LoadModule: "ramdac"
[   230.917] (II) Module "ramdac" already built-in
[   230.917] (EE)
Fatal server error:
[   230.917] (EE) AddScreen/ScreenInit failed for driver 0
[   230.917] (EE)
[   230.917] (EE)
Please consult the The X.Org Foundation support
         at http://wiki.x.org
 for help.
[   230.917] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[   230.917] (EE)
[   230.935] (EE) Server terminated with error (1). Closing log file.
```
It's not a GPU instance, so I've used X-dummy driver, following the instructions from the NICE DCV Administrator guide.

Answer

The X server cannot start because you have an error in xorg.conf.  Please compare your configuration to the documentation.

If you do not find the cause you can show the xorg.conf here so we could have a look into it.

Answer

Hi, i also have the same error, and i've followed the official documentation . my instance type is "m5ad.2xlarge" , ubuntu 22.04 without a GPU attached. 
also it seems that Nice DCV display does not scale to screen size for instances without a GPU.
any help with this is very much appreciated.

NICE DCV post-installation check error xhost: unable to open display "0"

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