I have same issue.
Screenshot: https://i.imgur.com/wyND39m.png
.blend file:

Blender Version
Broken: version: 2.81 (sub 3), branch: master, commit date: 2019-08-20 22:35, hash: rBdaba3e871ff5

Same here.
version: 2.81 (sub 3), branch: master, commit date: 2019-08-24 07:02, hash: b7f786c0b150, type: Release
GeForce GTX 750 Ti OC
AMD Phenom II X4 965 CPU
Win 10 x64

here work fine with @Evgeny (mortuusars) .blend test file on linux Blender 2.81 daba3e871ff5 (2019-08-20) AMD FX8350, 16GB DDR3, GTX690 2+2 GB VRam- Nvidia drivers 435.17, Factory Setting applied, LoadUI and Trusted Source disabled in file browser

Having the same problem with OIDN giving a black render result every time.
blender-2.81-daba3e871ff5-linux-glibc217-x86_64
Linux 4.15, 8GB DDR2, GeForce GTX 970, Nvidia driver 430.26

I can't reproduce the problem. Which CPU model do you have?

AMD Athlon(tm) 64 X2 Dual Core Processor 4400+ (family: 0xf, model: 0x6b, stepping: 0x1)
cpu MHz: 2300
cache size: 512kB (x2)

I think for Open Image Denoiser you need a cpu with SSE 4.1 or greater. Your cpu is too old!
See: https://openimagedenoise.github.io/
You can download cpu-z and see the extensions your cpu provides.

Ok, thanks @Marcus Papathoma (machieb) that's the explanation. On Linux /proc/cpuinfo shows the CPU feature flags which for me includes sse and sse2 but no higher.
Us with an old CPU but a newer Nvidia GPU can still use the Optix/Cuda denoiser and related Blender add-ons.

@Lauri Hastholm (laurijh) I don't have a CPU without SSE4.1, it would be great if you could leave feedback here if my fix worked for you. On unsupported CPUs, you should now see a message in the node itself and it should now act as a passthrough instead of returning a black image.

Commit d547f9d3d291 breaks builds, it's missing the BLi_system.h header on source/blender/editors/space_node/drawnode.c.

diff --git a/source/blender/editors/space_node/drawnode.c b/source/blender/editors/space_node/drawnode.c
index 72a73f89227..b89f163f579 100644
--- a/source/blender/editors/space_node/drawnode.c
+++ b/source/blender/editors/space_node/drawnode.c
@@ -24,6 +24,7 @@
 
 #include "BLI_blenlib.h"
 #include "BLI_math.h"
+#include "BLI_system.h"
 
 #include "DNA_node_types.h"
 #include "DNA_object_types.h"

In T68944#763645, @Stefan Werner (swerner) wrote:

@Lauri Hastholm (laurijh) I don't have a CPU without SSE4.1, it would be great if you could leave feedback here if my fix worked for you. On unsupported CPUs, you should now see a message in the node itself and it should now act as a passthrough instead of returning a black image.

After a quick test I can say that it does work. There is a message saying that the node is disabled because SSE4.1 is required and the node act as a passthrough.

If you are using an existing template script to batch render, make sure you update your command line to use a path to Blender 2.81

example...
replace
C:\Program Files\Blender Foundation\Blender
with
C:\Program Files\Blender Foundation\Blender 2.81\

I have this same issue, but I have an AMD Ryzen 7 3700x which does support SSE4.1. I recently upgraded from an i7 6700, and that worked fine with the denoise node. I am using Blender 2.82 from the official Arch repos.

I'm getting the same issue. I dual boot macOS on this PC which didn't have the same problem, seems to only happen on my [Arch] Linux.

Blender 2.82a
CPU: Intel(R) Core(TM) i7-3770K CPU @ 3.50GHz
GPU: AMD RX 580
Arch Linux, X11, KDE

I've found the denoise nodes to only ouput black if there are too many of them. I'm guessing it's because they all get executed simultaneously rather than consecutively, so system resources get overwhelmed. There's an additional blend file to try in this report:

https://developer.blender.org/T77023

The denoise nodes that fail are random each time you render.

I'm only including it once, and it still has that problem.

is it a 4k render? Or perhaps you have other expensive nodes? It's happening for me only if my system runs out of ram whilst it's doing the compositing stage. What's your system ram and cpu usage when it's calculating the compositor?

No, its 1920x1080. I have 16 gigs of ram, it only uses around 1-2 gigs

hmm, not sure then. Should work on AMD apparently. Maybe try 2.9 and see if that's any better.

I'm a beginner and doing a very simple tutorial (donut) with only 1 denoise node. Like I said, it works when I boot into my macOS, but not in Linux.

@gregorystarr00@gmail.com (captainpicard99) & @Nick Enchev (Hastouki) The Arch version of OIDN that is used to build the Arch version of Blender is corrupted. That is why you are getting this issue.
See https://github.com/OpenImageDenoise/oidn/issues/76#issuecomment-640953648

Please download the official version of Blender from the following link:

https://www.blender.org/download/