Cannot start R or Python sessions: HttpError HTTP request failed

[ianfiske]

System details:

Positron and OS details:

Positron Version: 2025.08.0 build 130
Code - OSS Version: 1.102.0
Commit: 76ddce5
Date: 2025-08-01T20:08:51.894Z (3 wks ago)
Electron: 35.6.0
Chromium: 134.0.6998.205
Node.js: 22.15.1
V8: 13.4.114.21-electron.0
OS: Darwin arm64 24.6.0

Session details:

R 4.5.1

Describe the issue:

I start Positron, and I get the error

R 4.5.1 failed to start.
HttpError
HTTP request failed

in the Console tab when R tries to start, every time.

Steps to reproduce the issue:

1. I start Positron.
2. I look at the console.
3. I have tried both transport mechanisms (IPC and TPC) and the result is the same.

Expected or desired behavior:

R should start in the console.

Were there any error messages in the UI, Output panel, or Developer Tools console?

In the Kernel Supervisor output I see

2025-08-27 09:19:23.657 [info] 13:19:23 [Positron] Starting Kallichore server /Applications/Positron.app/Contents/Resources/app/extensions/positron-supervisor/resources/kallichore/kcserver with connection file /var/folders/my/yl_zxl4n3tlfwxwy9grcrg2h0000gp/T/kallichore-3db107ba-70126.json
13:19:26 [Positron] Read domain socket connection information from /var/folders/my/yl_zxl4n3tlfwxwy9grcrg2h0000gp/T/kallichore-3db107ba-70126.json: /var/folders/my/yl_zxl4n3tlfwxwy9grcrg2h0000gp/T/kc-71405.sock, constructed base path: http://unix:/var/folders/my/yl_zxl4n3tlfwxwy9grcrg2h0000gp/T/kc-71405.sock:
13:19:26 [Positron] Failed to get initial server status from Kallichore; server may not be running or may not be ready. Check the terminal for errors. Error: {"response":{"statusCode":400,"headers":{"content-length":"0","date":"Wed, 27 Aug 2025 13:19:26 GMT"},"request":{"uri":{"protocol":"http:","slashes":true,"auth":null,"host":"/var/folders/my/yl_zxl4n3tlfwxwy9grcrg2h0000gp/T/kc-71405.sock","port":80,"hostname":"/var/folders/my/yl_zxl4n3tlfwxwy9grcrg2h0000gp/T/kc-71405.sock","hash":null,"search":null,"query":null,"pathname":"/status","path":"/status","href":"http://unix/var/folders/my/yl_zxl4n3tlfwxwy9grcrg2h0000gp/T/kc-71405.sock:/status","isUnix":true},"method":"GET","headers":{"Accept":"application/json","Authorization":"Bearer f25dabc1dc2323ef"}}},"statusCode":400,"name":"HttpError"}
13:19:26 [Positron] Failed to start Kallichore server: HttpError: HTTP request failed

[jmcphers]

Thanks for trying both IPC mechanisms and reporting the logs! I don't see anything useful in there, which is unusual since the supervisor should be outputting at least something ...

Can you try the following to capture more info?

• Run the command Developer: Set Log Level... and set the log level to Trace.
• In the Settings UI, go to Kernel Supervisor > Show Terminal and enable the setting.
• Reload the Positron window by running the Developer: Reload Window command.
• Attempt to start an R session again.
• Let us know what you see in the Kernel Supervisor logs and the supervisor terminal (in the Terminal tab).

[juliasilge]

We've got a number of users who are reporting problems with this:

• Local interpreters failed to start #9248
• Help/Viewer can be blank due to inappropriate HTTP proxy use #8426 (comment)
• Help/Viewer can be blank due to inappropriate HTTP proxy use #8426 (comment)

Looks like mostly macOS, and a mix of problems with local and remote SSH or WSL sessions. Most people seem to report the problems started with a recent release.

Unfortunately, we don't currently have an idea of what might be going in the case of starting Python/R sessions but let's move this along to triage for prioritization and evaluation.

[wurucheng123]

Hi, I also encountered the same issue. It seems still work for me in the version 2025.07.0-204, but I encountered the issue after the version 2025.08.0-130.

[jmcphers]

For anyone affected by this problem... would you be willing to try running the supervisor in one of Positron's Terminals? On e.g. macOS:

% cd /Applications/Positron.app/Contents/Resources/app/extensions/positron-supervisor/resources/kallichore
% ./kcserver --log-level trace --transport socket

This won't fix the problem, but might emit a more useful error.

[wurucheng123]

I saw the following standard output after I ran the commands on the local terminal in my positron.

03:38:09 [INFO] Using Unix domain socket: /var/folders/tj/j92cz1_x0s752030m90271sr0000gn/T/kc-6390.sock
Listening on Unix socket: /var/folders/tj/j92cz1_x0s752030m90271sr0000gn/T/kc-6390.sock
03:38:09 [INFO] Generated random auth token: 8d935aceb26e06c2

  ,            _   _           _
 /|   /       | | | | o       | |
  |__/   __,  | | | |     __  | |     __   ,_    _
  | \   /  |  |/  |/  |  /    |/ \   /  \_/  |  |/
  |  \_/\_/|_/|__/|__/|_/\___/|   |_/\__/    |_/|__/
  A Jupyter Kernel supervisor. Version 0.1.52.
  Copyright (c) 2025, Posit Software PBC. All rights reserved.

03:38:09 [DEBUG] (1) kcserver: Starting Kallichore
03:38:09 [DEBUG] (8) kcserver::server: idle_shutdown_hours not specified; the server will not shut down due to inactivity