Arch Linux User Repository

@juancarlospaco this is easily done on your own system, not in a PKGBUILD, given that building packages runs as root:

sudo groupadd unrealengine-users
sudo usermod -aG unrealengine-users (your-username)
sudo chown -R root:unrealengine-users /opt/unreal-engine
sudo chmod -R 775 /opt/unreal-engine

Permission issues like this are already mentioned on the UE Arch wiki page: https://wiki.archlinux.org/title/Unreal_Engine_4#Installing_from_the_AUR

This is a user system problem; I already did what I could without needing users to do the above by giving the 777 permissions. If it still gives you trouble, you'll have to use the example to solve it or change the install location to somewhere you have user permissions by default (as I cannot do this for you).

Will update to 5.0 when it is released.

@neko-san from the Unreal directory, try

recompiling the engine first with make ARGS=-ForceUseSystemCompiler

./GenerateProjectFiles.sh -project="/PathToProject/ProjectName.uproject" -ForceUseSystemCompiler -game -engine -makefile

Then run, in the project folder make ProjectNameEditor ARGS=-ForceUseSystemCompiler

If it still won't open run: make ProjectName ARGS=-ForceUseSystemCompiler

If that still doesn't sometimes going through it again works. The process might be a little faster with ccache turned on.

If you're not using the system compiler remove that part. There also might be shader issues that need to be corrected prior to being able to open the project in engine.

@Neko-san, I would not at all recommend Wine for Unreal Engine/game development as an Editor. There are far too many incomplete/imprecise/unsure APIs and odds+ends to think of. If I were testing...non-production, I'd just patch Unreal Engine to not complain and do a 'final build' on Windows with the small toolchain (just install it, restart PC, Linux builds will be available through editor, automagically). That way you can help dev on Linux and test locally and have the Windows devs stick to their environment.

Unreal Engine is strict to prevent tracking down obscure bugs and such. Unity uses C# .NET which uses Mono on Linux. Mono does not implement everything correctly, such as PropertyGrid sorting which can cause crashes on its own. Every platform has their own issue. As I suggested before, for development you could simply patch the version fussing and only do 'final builds' from Windows with the easy-to-setup toolchain. The toolchain from Windows is the official way of doing things.

@OdinVex Would using Wine be more beneficial then since the code is basically the same and UE4 is only really complaining about a non-issue?

I'd really prefer to develop with the system I'm using; it's stupid that Unreal isn't smart enough to realize that there's no actual difference in the project. Eats storage space for lunch and isn't even as intelligent as Unity to tell the difference about something so basic.

@Neko-san, The problem with using any C++ is that Unreal fusses about different build 'versions' even if they're the same version but different compile. You can compile Unreal back to back on the same machine for the same machine and the builds are different, simply because it is another build compilation. When trying to use anything with C++, it'll fuss about incompatibilities. Any time you pass back and forth between two non-same builds, you'll get those fussings. You will need to recompile every single time or do what some small studios do (which can be a headache to maintain): Patch this fussing out and simply remember to recompile on any engine changes. If you're going to compile for Linux and Windows, it is better (at the moment) to compile using Windows with a toolchain for Linux instead.

@OdinVex My project teammates use Windows and I use Linux As for the project itself, it's a project with a C++ module; so I take it you mean that in order for me to open the project, the project needs to use a compatible toolchain instead of whatever it's using?

(I haven't used Windows in a long time and I'm trying to figure out UE4's weird design choices)

@zerophase, Attempting to overwrite version-detection via INI variables has rarely worked, much of Unreal Engine uses hard-coded (during compile-time) versions when comparing builds. (I'm talking about Plugins used or C++ projects that may need to be cleaned before compiling again.)

@neko-san I'm not sure how to exactly do that. I believe there are some variables you can edit in one of the engine's ini files for saving stuff to your project directories and not engine. For the other errors maybe try recompiling the engine prior.

@Neko-san, If I follow you correctly, you're using a C++ project (or a BP project that uses modules/plugins in C++). I have often required compiling for multiple platforms and that has always come down to cross-compiling only. Eg, if your project was based on Windows then you need to use the (clang) Linux Cross-Compile Toolchain for Unreal Engine on Windows to compile for Windows (remember to reboot after installing it). If you're based on Linux I have bad news for you, there is no official way to cross-compile for non-Linux as of 2021/01/01.

For me, the Engine fails to compile pre-existing projects (from Windows) with and error about what was compiled would affect installed engine files (somehow)

It also refuses to open the project if the Makefile was run with in the terminal as well

------- Build details --------
Using toolchain located at '/opt/unreal-engine/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v17_clang-10.0.1-centos7/x86_64-unknown-linux-gnu'.
Using clang (/opt/unreal-engine/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v17_clang-10.0.1-centos7/x86_64-unknown-linux-gnu/bin/clang++) version '10.0.1' (string), 10 (major), 0 (minor), 1 (patch)
Using bundled libc++ standard C++ library.
Using lld linker
Using llvm-ar : /opt/unreal-engine/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v17_clang-10.0.1-centos7/x86_64-unknown-linux-gnu/bin/llvm-ar
Using fast way to relink  circularly dependent libraries (no FixDeps).
------------------------------
ERROR: Building would modify the following engine files:

       /opt/unreal-engine/Engine/Binaries/Linux/AgentInterface.dll
       /opt/unreal-engine/Engine/Binaries/Linux/Android/libUE4Editor-AndroidDeviceDetection.so
       /opt/unreal-engine/Engine/Binaries/Linux/Android/libUE4Editor-AndroidPlatformEditor.so

(and many more; too many to fit here)

and doing it in the terminal seems to work but doing so compiles what's needed on my OS drive which is low on space from the engine enough as it is x_x

Would be great if it did that in the project folder so it doesn't eat my SSD alive)

I read in a compilation guide from Epic to use chmod -R a+rwX on UnrealEngine/Engine after everything is "said and done installed". I've never had permissions issues or crashes (relating to permissions, hah...).