UE Build Lighting 0% - MacOS Solution - Dec 2022

Hello, Mac users! I found the definitive solution to Build lighting stuck at 0%. It is pretty simple but it took me two years to figure it out! It has everything to do with permissions to the UnrealLightmass file. It is located wherever your version of the engine is kept ie: ~/UE_5.1/Engine/Binaries/Mac/UnrealLightmass. I keep all my engine instances on an external thunderbolt drive.

Step 1: Make sure you do have the UnrealLightmass file added to your MacOS firewall under System Preferences/Security & Privacy/Firewall/Firewall Options. Click the (Add) + button and navigate to the UnrealLightmass file and Allow Incoming connections. If you haven’t done so already. Now OK and close your Preference panel.

Step 2: Simply double-check any other software you may have installed such as “Little Snitch” and they are not blocking any UE related tasks.

Step 3: Go to the “UnrealLightmass” file via your finder window and select it.

Step 4: The answer you have been waiting for… Right-click that file and Get Info. look at Sharing and Permissions and make sure every account you have listed there is set to Read & Write. I had my user account on Read & Write but the Staff and Everyone were on Read-only. I changed those two and the problem was solved!

Step 5: Go to your project and Build your lighting!

I really hope this helps, if anyone still has issues I will be happy to try and help you.
Good luck! :smiley:

I have to amend my post to say: The next day I seemed to go back to square one. After doing all this work, I couldn’t build the lighting! After further investigation and a few more tests, I found that I had to disable my MacOS firewall completely. I thought I could narrow it down by deleting all epic-related processes, but that didn’t do it. So as a test I proceeded to build the lighting for my project, and while that was happening I disabled the firewall. As soon as I did that, the build lighting started immediately. To recap, I would still complete the steps in my first post and disable the macOS firewall. You should be good to go. :sweat_smile:

This topic has been moved from International to Development: Rendering.

When posting, please review the categories to ensure your topic is posted in the most relevant space. Hopefully, this new category change will help others to get an answer.

Happy Developing! :slight_smile:

Hi PresumtivePanda, How are you? Thanks for moving this to a better spot. However, I am not looking for an answer. In this case, I am providing one. The question is very common among Mac users and I have been searching for a solution for a long time and I finally figured it out.
If you think there is a better spot for this please let me know. I am just getting used to using the forum.
Thanks for your moderation! Have a good day! :smiley:

Oh, sorry! My mistake :slight_smile: I’ll keep it in the rendering category as it’s where people with similar questions would look. Thanks for helping me to fix that!

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Hi Troy Graves,

I’m a little bit late to the Party but sadly your workaround doesn’t seems to work for me. I have the same problem but with version 5.2.1. The Building Light stuck at 0 % with the difference of failing after a view minutes. The Message Log shows ‘WorldSetting Maps needs lighting rebuild’. I have no idea what that means. After a lot of googling, the only thing I can found is, something is wrong with the ‘Swarm’. Unreal says Swarm is only available on windows. Because of that and Swarm seems to be something with the network, I come up with your solution. After testing a lot, I figured out version 5.1.2 can building lighting without any problems. 5.2 - 5.3 are failing.

Maybe you have a solution with versions above 5.1.

Hi NervKotz_Dev So sorry for the late response! I just logged in today and found your message. You will never be too late for this party. I just posted this to help anybody over time. MacOS gets a little neglected as you know.

Did you make any progress with it yet? So far I haven’t had any trouble with 5.2. I have used 5.3 a few times so I will double-check my project just to make sure. So far it has been good as well.
The first thing that comes to my mind would be to check if anything else might have blocked your network connections. If you use Little Snitch or another firewall application, also if your host was modified for some reason make sure that it is clean.

Hi Troy, hello NervKotz_Dev,
I ran into the same issue with the lighting build being stuck at 0%.
While searching for a solution, I found two different cases and I’m at the moment not 100% sure of a solution.
But everytime I deactivate the firewall it works, active firewall no lighting build. A few days ago, I was working on the train and being on a smartphone hotspot it seemed to work, but I’m not sure, if I had the firewall active at the time. I don’t know which part of the process gets block, but the solution can’t be to add 18(all Lightmass-programms) exceptions to the firewall.
Currently I’m using 5.3.2-29314046+++UE5+Release-5.3 on a M3 max.
My solution for the moment is to work with an inactive firewall, and I switch it on after the first lighting build. It seems to work then, but it falls back to build nothing after hibernation.