Console error on startup

[spcatterall]

Hi,
I thought I'd try Positron today. I installed it, but have run into an error which sounds similar to that described in #8008. I am using this version on Windows 10.

Positron Version: 2025.08.0 (system setup) build 11
Code - OSS Version: 1.100.0
Commit: 36d51df
Date: 2025-06-30T04:01:02.626Z
Electron: 34.5.1
Chromium: 132.0.6834.210
Node.js: 20.19.0
V8: 13.2.152.41-electron.0
OS: Windows_NT x64 10.0.17763

At startup I get the following message on the console:

R 4.5.0 failed to start.
Error
The supervisor process exited unexpectedly during startup

I also get a message:
The terminal process "c:\Program Files\Positron\resources\app\extensions\positron-supervisor\resources\supervisor-wrapper.bat 'C:\Users\stephen\AppData\Local\Temp\kallichore-32adee81-11580.out.log', 'c:\Program Files\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe', '--log-level', 'debug', '--log-file', 'C:\Users\stephen\AppData\Local\Temp\kallichore-32adee81-11580.log', '--connection-file', 'C:\Users\stephen\AppData\Local\Temp\kallichore-32adee81-11580.json', '--idle-shutdown-hours', '1'" terminated with exit code: 1.

Does anyone know a way round this? Thanks.

[juliasilge]

Oh, I'm sorry to hear that! Do you see the same or a different stack trace in your R kernel log, compared to what is outlined in #8008 (reply in thread)?

You can read about how to get to this and other logs at https://positron.posit.co/troubleshooting.html#python-and-r-logs.

[spcatterall]

Hi, thanks for your reply, I can't see any R kernel log, but have attached a couple of the log files that I can see.
Kernel Supervisor.log
R Language Pack.log

[jmcphers]

Thank you for the logs! The most common cause of this problem that we've observed is antivirus software on the machine thinking that kcserver.exe (the program that runs R and Python sessions) is a virus, and blocking or removing it. Can you try adding an exclusion for it? Docs here:

https://learn.microsoft.com/en-us/defender-endpoint/configure-exclusions-microsoft-defender-antivirus#configure-custom-exclusions-for-microsoft-defender-antivirus

A few more reports you can read for more context/ideas:

#5905
#8000

We have reported this problem to Microsoft and are also working on some improvements to the kcserver.exe program to make it look less suspicious.

Let us know if that fixes it for you!

[spcatterall]

Many thanks for your reply. I've tried allowing Positron and kcserver.exe to communicate through the firewall, but that did not seem to make any difference. Unfortunately I don't think I have the appropriate permissions to add an exclusion for kcserver.exe. Looking at the 'threat history' for Windows Defender, I note that kcserver.exe has not been identified as a threat.

[chrismainey]

Nothing helpful to add, but I get the same message. Running under Windows 10. Will see if I can get IT provider to add as an exception, but same issue here:
"c:\Users\ChrisMainey(Birmingh\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\supervisor-wrapper.bat 'C:\Users\ChrisMainey(Birmingh\AppData\Local\Temp\kallichore-fb7ef398-33868.out.log', 'c:\Users\ChrisMainey(Birmingh\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe', '--log-level', 'debug', '--log-file', 'C:\Users\ChrisMainey(Birmingh\AppData\Local\Temp\kallichore-fb7ef398-33868.log', '--connection-file', 'C:\Users\ChrisMainey(Birmingh\AppData\Local\Temp\kallichore-fb7ef398-33868.json', '--idle-shutdown-hours', '1'" terminated with exit code: 1.

[chrismainey]

@jennybc , suspect you are right about username, but we've got an unhelpful organisational policy that forces things through OneDrive with awful usernames. That means temp directory / users folder on windows has to map to the OneDrive bit with the username. Wonder if there's a way to specify another temp location?
like @spcatterall , I can use VSCode and RStudio just fine, so must be something positron specific.

[jennybc]

Wonder if there's a way to specify another temp location?

@chrismainey The person in the story I linked to did try that and I think it worked (or at least yielded new information).

[chrismainey]

Thanks @jennybc . Tried the username fix, as that makes a lot of sense, but doesn't seem to be it. I what @jmcphers said is the issue as, when reinstalling on a clean path, I've got a Window's defender block. Will chase with IT provider to get kcserver added as a exception.

[chrismainey]

Thanks for the advice @jennybc and @jmcphers . It's all resolved and working now because it was Windows Defender blocking kcserver. Had to add it as an exception, but organisation defaults to installing things on OneDrive (and their OneDrive has invalid characters, is too long, and doesn't play nice with executions). Clean install in C:\Positron with Windows Defender exception for the folder solved it.

[spcatterall]

Yes, I've just tried again, and had to click "Allow access" to the Windows Security Alert popup, but Positron does now seem to be working for me. Thanks!