Cling kernel for Jupyter on Windows does not work

Dear Root Community,

I have the following problem: C++ cling kernels for Jupyter fail to run in Jupyter. I can see the icons for all 4 kernels but when I try any of the C++ cling kernels they fail to start with the error. Please see the screenshot attached.

C++ cling kernels for Jupyter run in Jupyter.

C++ cling kernels for Jupyter won’t start.

Error Starting Kernel

[WinError 2] The system cannot find the file specified


  1. install Windows 11 version 23H2
  2. follow official instructions on how to build cling on Windows. Build for llvm, clang and cling succeeded. cling --version shows 1.1~dev. I confirm that I can code freely from command line.
  3. install jupyter with mamba (conda) in a separate environment.
  4. make cling available through PATH along with everything that is in the build folder resulted from step 2.
  5. follow the official instructions on how to install C++ cling kernels for Jupyter from github (githubcom/root-project/cling/tree/aa6d4924b5c15290f4b7f019193daf417d81c121/tools/Jupyter) can’t post a full link due to the rules.
    No errors. Kernels appear in Jupyter’s interface.

Hi Nikolay,

Welcome to the ROOT community!
I add in the loop our Win expert @bellenot .


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I can reproduce the error, will try to figure out what is the problem

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So I don’t know if this was working on Windows. I know the ROOT notebook works, but never tried cling. Maybe @vvassilev knows how to debug this

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@bellenot Bertrand, thank you for looking into it. Did you have a chance to look deeper into it? Any advise?

Not yet, and I was hoping @vvassilev could give advice where to start from…

Hi all. Is that cling standalone or xeus-cling?

Hi! This is cling standalone. Thank you for hopping in!

AFAIK, the jupyter library in cling needs some glue to connect to the jupyter system. Is that what we are seeing now?

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