Supervisor process exits unexpectedly during startup

[laurenagardner]

I downloaded Positron on my device with Windows 11. I have the most recent version of R downloaded, and I have cleared any trace of previous R editions from my device. When I open Positron and try to "start session" there is a kernel supervisor error in the console. The output says:
2026-09-13 15:37:36.285 [info] Positron Kernel Supervisor activated
2026-09-13 15:37:36.285 [info] 19:37:35 [Positron] Listening for supervisor handshake on \.\pipe\kallichore-handshake-kallichore-4efd532b-11016
2026-09-13 15:37:36.285 [info] 19:37:35 [Positron] Using named pipe transport
2026-09-13 15:37:36.285 [info] 19:37:35 [Positron] Starting Kallichore server c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe with handshake socket \.\pipe\kallichore-handshake-kallichore-4efd532b-11016 and 15000ms startup timeout
2026-09-13 15:37:36.285 [info] 19:37:36 [Positron] Kallichore terminal started in 382ms with PID 11856
19:37:36 [Positron] Kallichore server PID 11856 is not running
19:37:36 [Positron] The supervisor process exited unexpectedly during startup; output:

c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe --log-level debug --log-file C:\Users\me\AppData\Local\Temp\kallichore-4efd532b-11016.log --handshake-socket \.\pipe\kallichore-handshake-kallichore-4efd532b-11016 --resource-sample-interval 1000 --transport named-pipe --idle-shutdown-hours 1

19:37:36 [Positron] Failed to start Kallichore server: Error: The supervisor process exited unexpectedly during startup; output:

c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe --log-level debug --log-file C:\Users\me\AppData\Local\Temp\kallichore-4efd532b-11016.log --handshake-socket \.\pipe\kallichore-handshake-kallichore-4efd532b-11016 --resource-sample-interval 1000 --transport named-pipe --idle-shutdown-hours 1

19:37:37 [Positron] Supervisor terminal closed (the process exited) with exit code -1073741515; output:
c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe --log-level debug --log-file C:\Users\me\AppData\Local\Temp\kallichore-4efd532b-11016.log --handshake-socket \.\pipe\kallichore-handshake-kallichore-4efd532b-11016 --resource-sample-interval 1000 --transport named-pipe --idle-shutdown-hours 1

19:38:01 [Positron] Listening for supervisor handshake on \.\pipe\kallichore-handshake-kallichore-a8971eed-11016
19:38:01 [Positron] Using named pipe transport
19:38:01 [Positron] Starting Kallichore server c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe with handshake socket \.\pipe\kallichore-handshake-kallichore-a8971eed-11016 and 15000ms startup timeout
19:38:02 [Positron] Kallichore terminal started in 454ms with PID 13256
19:38:02 [Positron] Kallichore server PID 13256 is not running
19:38:02 [Positron] The supervisor process exited unexpectedly during startup; output:

c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe --log-level debug --log-file C:\Users\me\AppData\Local\Temp\kallichore-a8971eed-11016.log --handshake-socket \.\pipe\kallichore-handshake-kallichore-a8971eed-11016 --resource-sample-interval 1000 --transport named-pipe --idle-shutdown-hours 1

19:38:02 [Positron] Supervisor terminal closed (the process exited) with exit code -1073741515; output:
c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe --log-level debug --log-file C:\Users\me\AppData\Local\Temp\kallichore-4efd532b-11016.log --handshake-socket \.\pipe\kallichore-handshake-kallichore-4efd532b-11016 --resource-sample-interval 1000 --transport named-pipe --idle-shutdown-hours 1

19:38:02 [Positron] Supervisor terminal closed (the process exited) with exit code -1073741515; output:
c:\Users\me\AppData\Local\Programs\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe --log-level debug --log-file C:\Users\me\AppData\Local\Temp\kallichore-a8971eed-11016.log --handshake-socket \.\pipe\kallichore-handshake-kallichore-a8971eed-11016 --resource-sample-interval 1000 --transport named-pipe --idle-shutdown-hours 1

I am new to this, and I have tried to find a workaround online, but much of it goes over my head and/or seems to lead to a dead end. I don't want to mess up my new device trying to get a program to work. Any suggestions?

[dhruvisompura]

Thanks for the detailed logs @laurenagardner!

The exit code -1073741515 means Windows couldn't find a required DLL when starting the kernel supervisor (the background process that manages your R and Python sessions). That almost always means the Visual C++ Redistributable isn't installed. Positron depends on it, but doesn't currently check for it or explain the error when it's missing 😅.

The install page links out to this step as a pre-requisite here (although its easy to miss!): https://positron.posit.co/download.html#windows-setup

Could you try the following and see if that resolves the problem for you:

1. Download the latest Visual C++ Redistributable (x64) from Microsoft: https://learn.microsoft.com/en-us/cpp/windows/latest-supported-vc-redist?view=msvc-170#latest-microsoft-visual-c-redistributable-version
2. Run the installer.
3. Restart Positron and try starting an R session again.

We're tracking improving the error messaging around this problem in #14848. Feel free to upvote/comment if you have any additional feedback about this!