Positron error on start-up, R failure to start

I'm running Windows 11 and have Positron installed. When I start Positron I see this error:

The terminal process "c:\Program Files\Positron\resources\app\extensions\positron-supervisor\resources\supervisor-wrapper.bat 'C:\Users\MANDEL~1\AppData\Local\Temp\kallichore-d4ca8625-27280.out.log', 'c:\Program Files\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe', '--log-level', 'debug', '--log-file', 'C:\Users\MANDEL~1\AppData\Local\Temp\kallichore-d4ca8625-27280.log', '--connection-file', 'C:\Users\MANDEL~1\AppData\Local\Temp\kallichore-d4ca8625-27280.json', '--resource-sample-interval', '1000', '--transport', 'named-pipe', '--idle-shutdown-hours', '1'" terminated with exit code: 1.

followed by this in the console:

R 4.5.3 failed to start.
The supervisor process exited unexpectedly during startup


Error: The supervisor process exited unexpectedly during startup
	at t.KCApi.start (c:\Program Files\Positron\resources\app\extensions\positron-supervisor\dist\extension.js:2:76393)

I have tried uninstalling R, Positron, Rstudio, nuking any remaining R folders and reinstalling but have not been able to fix the problem. Rstudio will open and R will work in Rstudio no problem. I'm not sure if this problem is related, but I can't install any source packages. I try and I get this uninformative warning:

> install.packages('dplyr', type = 'source')
Installing package into ‘C:/Users/Mandelbrat/R/library’
(as ‘lib’ is unspecified)
trying URL 'https://cran.rstudio.com/src/contrib/dplyr_1.2.1.tar.gz'
Content type 'application/x-gzip' length 923509 bytes (901 KB)
downloaded 901 KB


The downloaded source packages are in
	‘C:\Users\Mandelbrat\AppData\Local\Temp\RtmpUZ9BAm\downloaded_packages’
Warning message:
In utils::install.packages("dplyr", type = "source") :
  installation of package ‘dplyr’ had non-zero exit status

I have my Rtools toolchain set up appropriately, I think. I haven't been able to solve this either.

If it's relevant here's my sessionInfo from Rstudio

> sessionInfo()
R version 4.5.3 (2026-03-11 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 10 x64 (build 19045)

Matrix products: default
  LAPACK version 3.12.1

locale:
[1] LC_COLLATE=English_United States.utf8  LC_CTYPE=English_United States.utf8    LC_MONETARY=English_United States.utf8
[4] LC_NUMERIC=C                           LC_TIME=English_United States.utf8    

time zone: America/Los_Angeles
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] compiler_4.5.3 tools_4.5.3   
1 Like

This sounds like a problem we resolved a few months ago! Does it still reproduce in the latest version? If not, can you share your Positron version from Help > About?

1 Like

Unfortunately I think I'm on the most recent version, or at least a very recent one
Positron Version: 2026.04.1 (system setup) build 10
Code - OSS Version: 1.109.2
Commit: 5dfc92424b4381ca7139f3f0a122a65abc2a9383
Date: 2026-04-14T01:26:22.333Z
Electron: 39.3.0
Chromium: 142.0.7444.265
Node.js: 22.21.1
V8: 14.2.231.22-electron.0
OS: Windows_NT x64 10.0.19045

And just to check, I downloaded the most recent version and still get the same issue occurring.

OK, maybe not the same issue!

  • Can you add a Runtime Startup Diagnostics report? (Generate one from the Command Palette)
  • Do you have any antivirus software running? If so, can you add an exception for kcserver.exe?

I added an exception to kcserver.exe to my Windows Defender and still see the error. Here's the diagnostic report:

Positron Runtime Startup Diagnostics

System Information

  • Positron: 2026.05.2 build 3 (Code OSS 1.109.2)
  • Commit: 1b5dfba9314510340cb08f2fedccc5ffba822beb
  • OS: win32(10.0.19045)
  • CPUs: AMD Ryzen 9 3900X 12-Core Processor (24 x 3800)
  • Memory(System): 63.93 GB (43.99GB free)
  • Initial Startup: true

Workspace-Affiliated Runtimes

  • No affiliated runtimes for this workspace

Active Sessions

  • No active runtime sessions

Time to First Runtime Ready

  • No runtime has reached ready state yet

Startup Phase Progression

  • Current Phase: Starting
Phase Timestamp (ms) Duration (ms)
initializing 1778878739535 -
awaitingTrust 1778878739535 0
starting 1778878740263 728

Positron Runtime Performance Marks

Name Timestamp Delta Total
code/positron/runtimeStartupBegin 1778878739534 0 0
code/positron/runtimeStartupPhase/initializing 1778878739535 1 1
code/positron/runtimeStartupPhase/awaitingTrust 1778878739535 0 1
code/positron/runtimeStartupPhase/starting 1778878740263 728 729
code/positron/runtimeStartup/extensionPreActivate/ms-python.python 1778878740311 48 777
code/positron/runtimeStartup/extensionPreActivate/positron.positron-r 1778878740311 0 777

Individual Session Startup Times

  • No session start marks recorded

Interpreter Settings

Startup Behavior

  • interpreters.startupBehavior: auto
  • interpreters.restartOnCrash: true

Python

  • python.defaultInterpreterPath: python
  • python.interpreters.include:
  • python.interpreters.exclude:
  • python.interpreters.override:
  • python.environmentProviders.enable: {"Venv":true,"Conda":true,"uv":true}
  • python.locator: native

R

  • positron.r.interpreters.default: (not set)
  • positron.r.customBinaries:
  • positron.r.customRootFolders:
  • positron.r.interpreters.exclude:
  • positron.r.interpreters.override:
  • positron.r.interpreters.condaDiscovery: false
  • positron.r.interpreters.pixiDiscovery: false

Session Launch Parameters

  • No active sessions

Discovered Runtimes

  • No runtimes have been discovered

Output Channels

  • No output channel content available
1 Like

@jonathan Just wanted to follow up to see if you had other suggestions for me. I'm about ready to just wipe my OS and reinstall everything because I'm so frustrated by this!

I was doing some digging in the Github Issues and saw some that looked similar, and other people asked to see the kernel supervisor log. Here's the log from my Kernel Supervisor:
2026-06-01 15:56:26.938 [info] Positron Kernel Supervisor activated

2026-06-01 15:56:26.938 [info] 22:56:26 [Positron] Generated connection file path: C:\Users\MANDEL~1\AppData\Local\Temp\kallichore-eb81dc58-34764.json

2026-06-01 15:56:26.938 [info] 22:56:26 [Positron] Using named pipe transport

2026-06-01 15:56:26.938 [info] 22:56:26 [Positron] Starting Kallichore server h:\Positron\resources\app\extensions\positron-supervisor\resources\kallichore\kcserver.exe with connection file C:\Users\MANDEL~1\AppData\Local\Temp\kallichore-eb81dc58-34764.json and 30000ms startup timeout

2026-06-01 15:56:26.938 [info] 22:56:26 [Positron] Kallichore terminal started in 643ms with PID 20140

22:56:27 [Positron] Kallichore server PID 20140 is not running

22:56:27 [Positron] The supervisor process exited unexpectedly during startup

22:56:27 [Positron] Failed to start Kallichore server: Error: The supervisor process exited unexpectedly during startup