April, May, and June have all shown up frequently in the past two or three months, and they are all Mac users. This kind of clustering is really unusual.
Finally I found the solution!
If you are trying to install Unreal Engine on macOS and the installation consistently fails around 70-75% with the error code IS-IN-FC02 (āOne or more files are corruptedā / āFileConstructionFailā in the logs), the problem is related to macOS system limits on open file descriptors.
Root Cause
During the final stage of installation (the file construction phase after chunks are downloaded), the Epic Games Launcher installer attempts to write and process over 10,170 files simultaneously (indicated by a high ActiveFileCount in the log files).
However:
-
By default, macOS limits GUI-launched applications to only 256 open files.
-
Even if you launch it via terminal with a higher limit, macOS has a hard kernel limit (
kern.maxfilesperproc) capped at 10,240 files per process. -
When the installer attempts to open the 10,241st file, macOS denies the file creation (manifesting in the logs as
Could not create ... (LastError=0)on files likeTransactionInlines.horUtils.h), causing the installer to crash and report it as a corrupted download.
The Fix (Temporary & 100% Safe)
To resolve this, you need to temporarily raise the macOS kernel limits and run the launcher from the Terminal so that the process inherits these higher limits.
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Quit the Epic Games Launcher completely (ensure no background helper processes are running by right-clicking the Dock icon and choosing Quit or Force Quit).
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Open the Terminal app.
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Temporarily increase the system-wide kernel file limits by running the following command (you will be prompted to enter your Mac administrator password):
sudo sysctl -w kern.maxfiles=131072 kern.maxfilesperproc=65536 -
Start the Epic Games Launcher from the same Terminal session, passing the higher shell limit (
ulimit):ulimit -S -n 65536 && "/Applications/Epic Games Launcher.app/Contents/MacOS/EpicGamesLauncher-Mac-Shipping" -
Click Resume on the Unreal Engine installation in the launcher. The installation will now complete successfully.
(Note: Once you restart your Mac, the kernel limits modified with sysctl -w will automatically reset back to macOS default values, making this a completely safe workaround).
Iām actually curious how you figured out the solution 
Iāve been bothered by this problem for several months.
I literally signed in just to say THANK YOU BRO
I can confirm that I had this same error and your method fixed it for me.
ur da goat
To be honest, it took me a few days of head-scratching and experimenting with different solutions before I finally arrived at this one! As a game programmer, Iām used to dealing with weird compilation and engine issues, but this installer crash was a different beast.
I started by digging through the Epic Games Launcher log files (~/Library/Logs/Unreal Engine/EpicGamesLauncher/EpicGamesLauncher.log). During the āFile Constructionā phase, I noticed it consistently failed on specific files with Could not create ... (LastError=0).
In Unix-based systems like macOS, a file creation failure that returns 0 (which normally means āsuccessā or āno errorā) is a classic indicator that the OS is refusing to allocate a new file descriptor (an EMFILE/ENFILE limit under the hood) and the applicationās file-handling wrapper fails to capture a specific error code.
Looking closely at the logs right before the crash, I saw that the ActiveFileCount (the number of chunk files the installer was writing and processing simultaneously) was climbing past 10,170.
Thatās when I looked into macOS resource limits:
- By default, macOS caps GUI-launched apps (like double-clicking the Launcher icon) to a tiny limit of 256 open files.
- Even if you run it from a standard terminal session to increase that, the macOS kernel has a hard cap (
kern.maxfilesperproc) that defaults to 10,240.
Because the UE 5.x installer tries to open slightly more than 10,200 files concurrently to reconstruct the engine files, it crashed the exact second it attempted to open the 10,241st file.
To bypass this, just using ulimit in the terminal wasnāt enough because the kernel limit of 10,240 would still block it. I had to:
- Use
sysctlwithsudoto temporarily raise the system-wide kernel cap (kern.maxfilesperproc). - Use
ulimit -nin that terminal session so the shell could exceed the old default limit. - Run the launcher executable directly from that terminal session so it inherited both the shell and kernel limits.
Really glad it saved you from more months of frustration!
Thanks bro! Iām genuinely happy to hear it worked and got you sorted out! 
Downgrading the launcher using third-party sites like Uptodown is pretty risky security-wise. On top of that, the launcher forces auto-updates anyway; I noticed that the workarounds to disable launcher updates seem to work on Windows, but they donāt work on Mac, making it really hard to keep it on an old version.
The command-line/kernel workaround lets you use the official, unmodified launcher downloaded directly from Epic, keeping it fully updated and secure, in the hope that theyāll officially patch this limit soon.