Linux Virtual Desktop Graphics Configuration and Troubleshooting


This document serves a guide for Linux VDA 1.3 Graphics configuration and fine-tuning. For system requirements and installation guide, please refer to Linux VDA Installation Guide on Citrix Documentation.

Configuration Parameters

There are quite a few configuration parameters under HKLMSystemCurrentControlSetControlCitrixThinwire regrading to graphics that can be tuned with ctxreg utility.

How to Enable Thinwire Plus

Thinwire plus is enabled by default, for both standard VDA and 3D Pro.

How to Enable H.264

In addition to the Operating System requirement, H.264 has minimum requirement on Receiver version, if client does not meet the requirements, it will fallback to thinwire plus.

OS Windows Mac OS X Linux Android iOS Chrome OS
Minimum requirement for H.264 3.4 or later 11.8 or later 13.0 or later 3.5 5.9 1.4

Latest Receiver feature matrix is available here.

Run the following command to advertise H.264 encoding in VDA:

sudo ctxreg create -k “HKLMSystemCurrentControlSetControlCitrixThinwire” -t “REG_DWORD” -v “AdvertiseH264” -d “0x00000001” –force

How to Enable Hardware Encoding in HDX 3D Pro

For HDX 3D Pro setting AdvertiseH264 only enables software H.264 encoding. Run this command to enable hardware encoding:

sudo ctxreg create -k “HKLMSystemCurrentControlSetControlCitrixThinwire” -t “REG_DWORD” -v “HardwareEncoding” -d “0x00000001” –force

Note: Currently, hardware encoding only supports H.240 YUV420P.

How to Tune Thinwire Plus for Lower bandwidth

  • MaxColorDepth

    Default 0x20, type DWORD.

    This option specifies the color depth of graphics transferred through thinwire protocol to client.

    To save bandwidth, set it to 0x10 (Preferred color depth for simple graphics) or 0x8 (the experimental low bandwidth mode).

  • Quality

    Visual quality

    Default: 0x1(medium), type: DWORD, valid values: 0x0(low), 0x1(medium), 0x2(high), 0x3(build to lossless), 0x4 always lossless.

    To save bandwidth, set Quality to 0x0(low).

Additional parameters

  • TargetFPS

    Target frame rate

    Default: 0x1e (30), Type: DWORD

  • MinFPS

    Target minimum frame rate

    Default: 0xa (10), Type: DWORD

  • MaxScreenNum

    Maximum number of Monitors client can have

    Default: 0x2, Type: DWORD

    For standard VDA, the maximum value can set is 10, and for 3D Pro, the maximum value can set is 4


Check which encoding is in use

Use the following command to check whether H.264 encoding is in use (1 means H.264 and 0 means TW+):

sudo ctxreg dump | grep H264

The results should resemble:

create -k “HKLMSoftwareCitrixIcaSession1Graphics” -t “REG_DWORD” -v “H264” -d “0x00000001” –force

create -k “HKLMSystemCurrentControlSetControlCitrixThinwire” -t “REG_DWORD” -v “AdvertiseH264” -d “0x00000001” –force

Check whether hardware encoding is in use for 3D pro

Run this command (0 means not in use, 1 means in use):

sudo ctxreg dump | grep HardwareEncoding

The results should resemble:

create -k “HKLMSoftwareCitrixIcaSession1Graphics” -t “REG_DWORD” -v “HardwareEncoding” -d “0x00000001” –force

Another way is to use nvidia-smi command, output should be like the following if hardware encoding in use:


Tue Apr 12 10:42:03 2016


| NVIDIA-SMI 361.28 Driver Version: 361.28 |


| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |

| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |


| 0 GRID K1 Off | 0000:00:05.0 Off | N/A |

| N/A 42C P0 14W / 31W | 207MiB / 4095MiB | 8% Default |



| Processes: GPU Memory |

| GPU PID Type Process name Usage |


| 0 2164 C+G /usr/local/bin/ctxgfx 106MiB |

| 0 2187 G Xorg 85MiB |


Check the NVIDIA GRID™ graphics driver is installed correctly

In order to verify if the NVIDIA GRID™ graphics driver is installed correctly, run “nvidia-smi”; the results should resemble:



| NVIDIA-SMI 352.70 Driver Version: 352.70 |


| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |

| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |


| 0 Tesla M60 Off | 0000:00:05.0 Off | Off |

| N/A 20C P0 37W / 150W | 19MiB / 8191MiB | 0% Default |



| Processes: GPU Memory |

| GPU PID Type Process name Usage |


| No running processes found |


In some cases, e.g. the GPU pass through case, the output indicates that the video card is not loaded correctly. This may caused by the following script:


  • check the BusID in /etc/X11/ctx-nvidia-*.conf, if the BusID of Secion “Device” is like the following. It could be incorrect.

BusID “PCI:0:0:0”

  • check the output of lspci, find the video card you are going to choose, in the following case, the device shall use PCI:0:5:0, which is different form the ctx-nvidia-*.conf file.

00:05.0 3D controller: NVIDIA Corporation Device xxxx (rev xx)

In this situation, the ctx-nvidia-*.conf are not configured correctly. You shall modify the script /etc/X11/ of line, to get correct gpu line according to the output of lspci

gpu=$(lspci | grep ‘VGA’ | grep ‘NVIDIA’)

When you modified the script, run the script by root again. So the /etc/X11/ctx-nvidia-*.conf are with the correct BusID.

You need to reboot Linux to make modification take effect.

HDX 3D Pro multi-monitor redraw issues

If you are seeing redraw issues on screens other than the primary monitor check that the NVIDIA GRID™ license is available.

Check Xorg error logs

The log file of Xorg is named like Xorg.{DISPLAY}.log under /var/log/ folder.


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