cannot start c++ kernel

[Spivey Nickolsan]

I'm unable to start the c++ kernel.

• [I 2021-03-09 12:19:56.467 LabApp] Build is up to date
  \[W 2021-03-09 12:19:59.117 ServerApp] Notebook vectors/Untitled1.ipynb is not trusted
  [W 2021-03-09 12:19:59.151 ServerApp] Notebook vectors/Untitled2.ipynb is not trusted
  [I 2021-03-09 12:20:02.440 ServerApp] Kernel started: 5a64e01c-9c1f-4946-a511-b58dd7ae4bae
  [I 2021-03-09 12:20:06.624 ServerApp] Kernel started: 9fa0e0fc-1ed5-4fc6-8899-05df3cbc97d7
  [I 2021-03-09 12:20:06.682 ServerApp] Kernel started: 4ae2acb5-8754-4cc2-861b-4f5381ed11ac
  [I 2021-03-09 12:21:05.986 ServerApp] Kernel shutdown: 9fa0e0fc-1ed5-4fc6-8899-05df3cbc97d7
  [I 2021-03-09 12:21:06.356 ServerApp] Kernel started: b16e42bc-229e-4002-8bbe-b4ca4eb37573
  [I 2021-03-09 12:21:12.354 ServerApp] AsyncIOLoopKernelRestarter: restarting kernel (1/5), keep random ports
  [I 2021-03-09 12:21:15.367 ServerApp] AsyncIOLoopKernelRestarter: restarting kernel (2/5), keep random ports
  [I 2021-03-09 12:21:18.383 ServerApp] AsyncIOLoopKernelRestarter: restarting kernel (3/5), keep random ports
  [I 2021-03-09 12:21:21.395 ServerApp] AsyncIOLoopKernelRestarter: restarting kernel (4/5), keep random ports
  [W 2021-03-09 12:21:24.409 ServerApp] AsyncIOLoopKernelRestarter: restart failed
  [W 2021-03-09 12:21:24.410 ServerApp] Kernel b16e42bc-229e-4002-8bbe-b4ca4eb37573 died, removing from map.
  [I 2021-03-09 12:22:00.586 ServerApp] Saving file at /vectors/Untitled1.ipynb
  [W 2021-03-09 12:22:06.433 ServerApp] Timeout waiting for kernel_info reply from b16e42bc-229e-4002-8bbe-b4ca4eb37573
  [E 2021-03-09 12:22:06.434 ServerApp] Error opening stream: HTTP 404: Not Found (Kernel does not exist: b16e42bc-229e-4002-8bbe-b4ca4eb37573)
  
  

[Kevin Bates]

Hi.  This issue is indicative of the program that Jupyter server is launching corresponding to your kernel is not running.  The AsyncIOLoopKernelRestarter is responsible for detecting unexpected process termination and will attempt to restart the process up to 5 times before giving up.  As a result, you should probably troubleshoot this from that aspect.

To locate the problematic command, follow the instructions in the last paragraph of this section of the documents: https://jupyter-notebook.readthedocs.io/en/latest/troubleshooting.html#python-environments.  It's unlikely that your issue is related to Python environments, but the instructions for locating the program (in the argv stanza of the kernel.json file) remain applicable.  Once the program has been identified, you might try starting it from the shell or some other way, to get more information as to why it doesn't remain running.  My guess is that there's a dependency that is not installed or available to that environment (so, I suppose it could be related to the python environment).

I would also recommend adding --debug to your jupyter lab start command to see if any DEBUG logging provides additional insights.

[Spivey Nickolsan]

Hi K,

Thanks for the detailed response. I think I've got this mostly solved now. I was having some other problems with conda. The unofficial package for my distribution defaulted to installing conda base/root at /usr and causing a lot of confusion for me. I noticed on the xeus-cling github, they say NOT to use conda but to use miniconda - I reinstalled jupyter and xeus-cling with miniconda - based in my home dir - and the kernel launches no problem now.

My next step is to try and enable code completion via jupyter-lsp language server protocol. The installation docs call for a specific env - conda create -c conda-forge -n lsp 'python >=3.7,<3.8' 'jupyterlab=2.2.0' 'nodejs >=10.12,<15' 'jupyter-lsp-python=0.9.3' - which I created and the kernel is not starting but the message is different.

• [I 18:44:40.874 LabApp] Build is up to date
• [I 18:44:49.578 LabApp] Creating new notebook in /[I 18:44:40.874 LabApp] Build is up to date
• [I 18:44:49.578 LabApp] Creating new notebook in /
• /usr/bin/xcpp: error while loading shared libraries: libsodium.so.23: cannot open shared object file: No such file or directory
• [I 18:44:50.372 LabApp] Kernel started: 6d146c42-8da5-42e6-9eef-88f79b90d3d0, name: xcpp17
• [I 18:44:53.370 LabApp] KernelRestarter: restarting kernel (1/5), new random ports
• /usr/bin/xcpp: error while loading shared libraries: libsodium.so.23: cannot open shared object file: No such file or directory

I'm still learning how to conda - do I need to explicitly install xeus-cling in this env again? Do all envs inherit from the base env but not from each other?

Hey, installing xeus-cling works  - I now have some basic code completion!