Jupyter Server Not Found (executable not in PATH)

[alejandroschuler]

Description

When starting jupyterlab_app, I get the message:

Jupyter Server Not Found
We were unable to launch a Jupyter server, which is a prerequisite for JupyterLab Native. If Jupyter is installed as a python module, but the python executable is not in your PATH, specify the executable location below. Otherwise, try installing or updating Jupyter. The Jupyter notebook version must be 4.3.0 or greater.

Despite a) having a working jupyter-lab installation that I can spin up from the terminal and which appears in the browser, b) having the python executable in my path, and c) having the requisite version of jupyter.

When I manually point jupyterlab_app to the python executable (/Users/aschuler/.pyenv/shims/python) via the CHOOSE PATH it spins the icon again for a moment and then returns the same "Server Not Found" message.

Context

I am running python through pyenv, which may be the issue here. Relevant information:

aschuler@Alejandros-MacBook-Air ~ % pyenv versions
  system
* 3.9.6 (set by /Users/aschuler/.pyenv/version)

aschuler@Alejandros-MacBook-Air ~ % echo $PATH    
/Users/aschuler/.pyenv/shims:/Applications/Sublime Text.app/Contents/SharedSupport/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/TeX/texbin

aschuler@Alejandros-MacBook-Air ~ % jupyter --version
jupyter core     : 4.7.1
jupyter-notebook : 6.4.0
qtconsole        : 5.1.1
ipython          : 7.26.0
ipykernel        : 6.0.3
jupyter client   : 6.1.12
jupyter lab      : 3.1.13
nbconvert        : 6.1.0
ipywidgets       : 7.6.3
nbformat         : 5.1.3
traitlets        : 5.0.5

aschuler@Alejandros-MacBook-Air ~ % which python
/Users/aschuler/.pyenv/shims/python

aschuler@Alejandros-MacBook-Air ~ % which jupyter-lab
/Users/aschuler/.pyenv/shims/jupyter-lab

(MK): Extra details from title: jupyterlab_app fails to start on MacOS 11.5.2 with (pyenv issue?)

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[alejandroschuler]

When I manually point jupyterlab_app to the python executable (/Users/aschuler/.pyenv/shims/python) via the CHOOSE PATH it spins the icon again for a moment and then returns the same "Server Not Found" message.

The problem occurs even if I point jupyterlab_app to the "true" python executable (not the pyenv shim), i.e. /Users/aschuler/.pyenv/versions/3.9.6/bin/python3.9.

[pybokeh]

Same thing happens with me, except I'm on Windows 10 OS. For some reason, it keeps thinking it should search for the python.exe located in the C:\JupyterLab folder despite me manually pointing it to the python.exe of the Python virtual env that has jupyterlab and server installed.

EDIT: I am using just venv module for my virtual environments, not pyenv.

[krassowski]

I think that jupyter_app was designed to be started from the icon file provided which takes care of selecting appropriate environment. For example on Ubuntu/GNOME this is an icon showing up in the application grid:

I expect that on Windows there is an icon in the start menu, and something similar on Mac. When you start jupyterlab-app from the menu entry/desktop icon does this error show up too?

[alejandroschuler]

@krassowski I was starting jupyter from the mac spotlight search (cmd-space -> "jupyter..." -> enter). I think this is the same as using the icon but I also just tried finding the icon in the application folder manually and double clicking and the result is the same.

[mbektas]

@alejandroschuler @pybokeh JupyterLab App bundles a Python environment and uses that environment explicitly. Clicking launcher icons are the right way to launch as @krassowski noted.

• On Mac have you installed JupyterLab App to default install destination (/Application/JupyterLab.app) or user directory ~/Applications/JupyterLab.app. Then your Python environment would be located in /Applications/JupyterLab.app/Contents/Resources/jlab_server or ~/Applications/JupyterLab.app/Contents/Resources/jlab_server. Can you confirm that is the case?
• On Windows make sure you don't change the default installation path of C:\JupyterLab. Your Python environment will be in C:\JupyterLab\resources\jlab_server. Please confirm that is the case. There is a known issue on Windows that subsequent launches of JupyterLab might sometimes fail after first launch as in "Jupyter Server Not Found" on Windows 10 #241. The workaround is to run the app as administrator. Can you check if that solves your problem?

[alejandroschuler]

@mbektas yes I can see /Applications/JupyterLab.app/Contents/Resources/jlab_server. What can I do to make the desktop app run the server from my installation?

[krassowski]

Is your goal to run a kernel from your installation, or to run a server from your installation? While I see a case for the former, I don't see when the latter would be required.

[alejandroschuler]

Is your goal to run a kernel from your installation, or to run a server from your installation? While I see a case for the former, I don't see when the latter would be required.

Ah, I see what you mean @krassowski. I would be more than content to run a kernel for my installation. That would suffice for packages installed via terminal pip to be accessible from jupyter, right?

Either way, it seems I can't even do that at the moment (i.e. the app fails to start even its own bundled server!)

[alejandroschuler]

Moreover, if the app is using its own installation of jupyter, why does the error message inform me that I should try to install or update jupyter?? That seems needlessly confusing.

[krassowski]

The error message was added a long time ago when the things worked differently and is probably worth replacing with something better (please feel welcome to contribute!). This app was just revived, please bear with us 🐻 while it is going through its infancy issues.

As for re-using kernels from other virtual environments/installations, it depends on the kernel, but when using IPython (ipykernel) you can:

1. Activate your old virtual environment with the ipython kernel you want to use
2. Execute ipython kernel install --name "My New Kernel" --user
3. Confirm that it was installed by running jupyter kernelspec list
4. Restart JupyterLab-App
5. See new kernel icon with My New Kernel label show up in the launcher
6. Try to import a package installed only in that kernel to verify that it works ok

Now, it works for me on Ubuntu but I don't have Windows/Mac to test it. It would be great if you could follow these steps and let us know how it goes.

[krassowski]

There is also nb_conda_kernels and jupyter_environment_kernels which allow for auto-discovery of kernels and maybe we should consider including those by default. This discussion is in #169 (comment).

[alejandroschuler]

@krassowski I'd love to try that, but, as I said, I can't get the app to even start the server. Based on my understanding, I can't really do anything about the kernel without a running server in the first place, right?