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.