Unreal Build Accelerator fails to generate ispc headers on Linux.

General Issues and Bug Reporting
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Summary

Unreal Build Accelerator fails to generate ispc headers on Linux with the default setup. Either disabling ISPC or UBA makes the editor compile.

The issues seems to have appeared somewhere between 5.4.4 and 5.5

Please select what you are reporting on:

Creative

What Type of Bug are you experiencing?

UI/Tools

Steps to Reproduce

  1. Follow the Linux compilation guide found at https://github.com/EpicGames/UnrealEngine/blob/ue5-main/Engine/Build/BatchFiles/Linux/README.md
  2. Observe the issues in the output log.
  3. Disable the UnrealBuildAccelerator via BuildConfiguration.xml (Build Configuration for Unreal Engine | Unreal Engine 5.6 Documentation | Epic Developer Community).
  4. Run make ARGS="-clean && make.
  5. Observe that the editor now compiles.
  6. Reenable UBA and disable ISPC compilation by changing bCompileISPC = true to bCompileISPC = false in Engine/Source/Programs/UnrealBuildTool/Platform/Linux/UEBuildLinux.cs.
  7. Run make ARGS="-clean && make.
  8. Observe that the editor now compiles

Expected Result

The editor compiles by default in Linux.

Observed Result

The editor doesn’t compile with the default Linux setup.

Platform(s)

Linux Editor

Additional Notes

Issues that mention this:

  1. Can't build 5.5.1 from source on Linux Mint (Ubuntu based) - #2 by GarrdThennson
  2. UE 5.5 Source Linux Compilation Errors - #2 by NuLL3rr0r
  3. Fix for ISPC Error When Building Unreal Engine 5.5 on Linux

Potentially related:

  1. ISPC Upgrading from Unreal Engine 5.3 to 5.5 no longer compiles on Windows On Arm for (x86_64) · Issue #3133 · ispc/ispc · GitHub
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Clarification:
Issue appears on release@2d53fcab0066b1f16dd956b227720841cad0f6f7 (release 5.5.4), doesn’t appear on ue5-main@e6c60b26d1c85e0f21f64a1402700b1712159156

3 Likes
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hi @AgentOfBurgundy ,
So basically this will mess will all official Ubuntu 22.04 and CentOS 7 , and don’t forget about
Debian 12, Fedora, Pop!_OS, and Arch Linux, Rocky 8

Things are bad enough now all the documentation is wrong now
Linux Development Quickstart for Unreal Engine | Unreal Engine 5.6 Documentation | Epic Developer Community

There was a lot of trouble with the Windows UBA version, which crashed early 5.5.*

Fortunately, 5.6 Windows is stable now and the edgy state-of-art is now 5.7.
Anyway voted this up, just couple more votes and it will be in the bug queue

1 Like
4

FORT-920749 has been created and its status is ‘Unconfirmed’. This is now in a queue to be reproduced and confirmed.

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5

were getting crash in packaging that says something about .psym files not being found or generated ? is this perhaps the same issue?

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My opinion is the same as others now, others should simply disable UBA on Linux.
BTW not seeing much performance increase on PC Windows for UBA

1 Like
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Turning OFF the UBA in the XML fixed my issues so far… it sems to be a UBA issue.

Screenshot 2025-06-08 191010
Screenshot 2025-06-08 1910102198×1094 229 KB

2 Likes
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It seems like UBA is marked as unsupported for Mac and Linux as indicated for 5.5 and 5.6.

So the real bug seems to be in the enabling of UBA by default on these platforms. Disabling UBA also seems to be the more ‘correct’ solution.

2 Likes
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From what I’ve tested so far it does seem to be an issue with Intel ISPC on machines with intel cpu’s. UBA functioned fine, or at least wasn’t throwing any tantrums on my desktop running an amd cpu.

so, leave the buildconfig xml file alone and just set the ISPC variable to false when building on a pc when intel for now.

1 Like
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For those trying to figure out where the vote button is, I found I had to scroll all the way back up to the top of the page and it’s on the top right side. Almost completely hidden.