When trying launch after successfully looking Linux build (./Setup.sh, then ./GenerateProjectFiles.sh, then make), launching the binary /Engine/Binaries/Linux/UE4Editor starts the editor as expected, but the attempt to rebuild the lights (I mean Build → Build Lightning only) caues the following crash:
[2018.01.14-11.10.55:842][ 0]LogLightmass: Processing...
Timed out waiting for the recipient (TimeWaitingSec = 60.007313)
[2018.01.14-11.11.55:849][ 0]LogInit: Error: Timed out waiting for the recipient (TimeWaitingSec = 60.007313)
UnrealLightmass: libdwarf_info.c:38: int _dwarf_info_first_cu(Dwarf_Debug, Dwarf_Error *): Assertion `dbg->dbg_cu_current == ((void*)0)' failed.
UnrealLightmass: libdwarf_info.c:38: int _dwarf_info_first_cu(Dwarf_Debug, Dwarf_Error *): Assertion `dbg->dbg_cu_current == ((void*)0)' failed.
[2018.01.14-11.11.56:329][738]LogLinux: Scale at X=0.000000, Y=32.000000: 1.000000 (monitor=#0, HDPI=96.000000 (horz scale: 1.000000), VDPI=96.000000 (vert scale: 1.000000))
[2018.01.14-11.11.56:329][738]LogLinux: Scale at X=1280.000000, Y=800.000000: 1.000000 (monitor=#0, HDPI=96.000000 (horz scale: 1.000000), VDPI=96.000000 (vert scale: 1.000000))
[2018.01.14-11.11.56:329][738]LogLinux: Scale at X=1280.000000, Y=800.000000: 1.000000 (monitor=#0, HDPI=96.000000 (horz scale: 1.000000), VDPI=96.000000 (vert scale: 1.000000))
[2018.01.14-11.11.56:392][738]LogLinux: Scale at X=0.000000, Y=32.000000: 1.000000 (monitor=#0, HDPI=96.000000 (horz scale: 1.000000), VDPI=96.000000 (vert scale: 1.000000))
[2018.01.14-11.11.56:392][738]LogLinux: Scale at X=1280.000000, Y=800.000000: 1.000000 (monitor=#0, HDPI=96.000000 (horz scale: 1.000000), VDPI=96.000000 (vert scale: 1.000000))
[2018.01.14-11.11.56:392][738]LogLinux: Scale at X=1280.000000, Y=800.000000: 1.000000 (monitor=#0, HDPI=96.000000 (horz scale: 1.000000), VDPI=96.000000 (vert scale: 1.000000))
[2018.01.14-11.11.56:411][738]LogSlate: Took 0.000287 seconds to synchronously load lazily loaded font '../../../Engine/Content/Slate/Fonts/Roboto-Light.ttf' (159K)
[2018.01.14-11.11.56:444][738]LogLinux: Setting swap interval to 'Immediate'
[2018.01.14-11.11.56:555][738]LogLinux: Setting swap interval to 'Immediate'
[2018.01.14-11.11.56:649][738]LogLinux: Error: appError called: Assertion failed: TaskDataArray.Num() == Exporter->VolumetricLightmapTaskGuids.Num() [File:/home/audrius/unreal/UnrealEngine/Engine/Source/Editor/UnrealEd/Private/Lightmass/ImportVolumetricLightmap.cpp] [Line: 843]
Import Volumetric Lightmap failed: Expected 64 tasks, only found 0
Signal 11 caught.
Malloc Size=131076 LargeMemoryPoolOffset=131092
The crash happens rather late into the build, after the message appears that the lights have been built and now in the process of installation.
Uname -a:
Linux Harold 4.4.0-109-generic #132-Ubuntu SMP Tue Jan 9 19:52:39 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
The machine uses original NVIDIA drivers as downloaded for CUDA development.
Does that happen when the machine is offline? Communication with the UnrealLightmass on Linux and Mac currently requires that the network interface supports multicast - you may have to enable it on the loopback interface.
No you still have to need a connection on my distro openSUSE also i had to do this step to allow unreal get the connection. So we have to enable this port on linux distros RCL it would be great if you include this in your commit so that in future releases this wont be to be done manually Thanks RCL for supporting linux
this kind of worked for me. It was more informative than right into my solution.
On CentOS 7.5, the lo does not mean anything, maybe in Ubuntu. On the firewall app, I had to make the WiFi conection to be trusted . . . yeah. So, if you’re conected to the internet by Ethernet, that one has to be the trusted conection. I noticed this until the 8th time I’ve downloaded the source from git from different releases, until I go the promoted version (4.22) this time. Almost a week to get to this answer that has a similar solution, I wanted to facepalm myself so hard, but this is something that has to be explained on the wiki. Even to write UnrealLightmass on the make compilation part, because seriously, after dedicating several days and many hours, no fast response on forums or even the IRC chat, people can lose their minds. I am thinking seriously on the crowdfound of the Launcher for Linux.
Thanks for your insight. I’m on Fedora and Ubuntu solution didn’t work for me. Can you elaborate more on what you did so I can try?
Do I set UE4 as trusted to make connections?
Check the image, it has instructions, very easy if you ask me.
Getting the solution was not easy, not because it was difficult. The real pain was getting the solution in a different way.
I believe firewall apps might be different for all Linux Distros. I hope the solution can be similar. You can try to post with pictures how is your firewall app, so we can spot the differences and get a solution. I hope in the future the Linux Build doesn’t need the firewall to build the lightmaps. that is kind of ridiculous since they don’t support cloud services for our platform yet.
Found it! Thanks for awesome how to. First 3 builds worked fine but then failed again with the same message. Good enough for me.
UE4 4.22p2 same issue. It occurs at random. I still don’t understand why I need fiddle with connection to build light…
I believe you Run Unreal from Console or terminal, you check why is not baking the Lightmaps, it should be always good. I installed the 4.21.2 the current release and it works as well as the Promoted version. There is a Java Launcher for the Market Place, it kind of works, but Epic should build an official version. If you’re interested or still having troubles PM me to have like an online meeting or make the Council of Unreal Editor Linux users hahaha
Thanks RCL for supporting linux 
