Unreal Engine 5.6 startup Vulkan error and VK_EXT_mesh_shader

Development Platform & Builds
1

After some recent commits, UE 5.6 stopped starting on Linux with the following error message:

[2025.02.14-15.05.40:828][ 0]Message dialog closed, result: Ok, title: Message, text: Failed to load Vulkan Driver which is required to run the engine.
The engine no longer fallbacks to OpenGL4 which has been deprecated.

It appears that this issue occurs when the GPU does not support VK_EXT_mesh_shader. Is this expected behavior—that VK_EXT_mesh_shader is required to start UE 5.6—or is it just a bug?

UE 5.5.3 starts correctly.

2

To hopefully add another data point to this: 5.5.4 returns the same error when starting while 5.5.3 doesn’t for me.

OS: Arch Linux
GPU: AMD RX 580 8GB (No VK_EXT_mesh_shader according to vulkaninfo)

3

you can edit DefaultEngine.ini and add
+TargetRHI=SF_VULKAN_SM5

to make it working in 5.4 but I expect some functionality may be lost

1 Like
4

Similar issue here:
Unreal 5.6 (Git from today throws the Vulkan error)
Unreal 5.5.4 works like expected (Downloaded from epics webside and not self-compiled)

[2025.03.29-20.26.10:664][ 0]LogVulkanRHI: Display: Registering provided Vulkan validation layers
[2025.03.29-20.26.10:664][ 0]LogVulkanRHI: Display: Updated VK_LAYER_PATH=../../../Engine/Binaries/ThirdParty/Vulkan/Linux:../../../Engine/Binaries/ThirdParty/Vulkan/Linux
[2025.03.29-20.26.10:664][ 0]LogVulkanRHI: Display: Updated LD_LIBRARY_PATH=../../../Engine/Binaries/ThirdParty/Vulkan/Linux:../../../Engine/Binaries/ThirdParty/Vulkan/Linux
[2025.03.29-20.26.10:665][ 0]LogVulkanRHI: Starting Vulkan Profile check for VP_UE_Vulkan_SM6:
[2025.03.29-20.26.10:754][ 0]LogVulkanRHI: - Unsupported extension: VK_KHR_compute_shader_derivatives
[2025.03.29-20.26.10:763][ 0]LogVulkanRHI: Vulkan Profile check complete.
[2025.03.29-20.26.10:763][ 0]LogRHI: Display: Skipping SF_VULKAN_SM6…
Shutdown handler: cleanup.

Message dialog closed, result: Ok, title: Message, text: Failed to load Vulkan Driver which is required to run the engine.
The engine no longer fallbacks to OpenGL4 which has been deprecated.

Same machine, same setup. Any news on this?

5

Same issue here. The error log gives a good hint:

LogVulkanRHI: - Unsupported extension: VK_KHR_compute_shader_derivatives

This extension was introduced with a certain Vulkan version:

In Unreal 5.5.4 I get the current Vulkan API verion:
LogVulkanRHI: Display: Built with Vulkan header version 1.3.290

On Nvidia driver side:

August 30th, 2024 - Windows 553.02, Linux 550.40.71

I am using a 560.76 feature driver which was recommend for using Vulkan with HWRT. This driver could be still on that older Vulkan version.

In 5.6 I get:
LogVulkanRHI: Warning: Found VULKAN_SDK=
LogVulkanRHI: Display: Built with Vulkan header version 1.4.304

I also get a pop up message for DX12 that SM6 is not supported. So it seems to be not only a Vulkan issue here.
Also the Vulkan SDK cannot be found.

So maybe we need to upgrade to latest driver for testing.

1 Like
6

Same here:
AMD Radeon RX 5700 XT

EDIT: seems to work with “+TargetedRHIs=SF_VULKAN_SM6” changing to “+TargetedRHIs=SF_VULKAN_SM5”

1 Like
7

Looks like 570 Nvidia Driver is working.