Jupyter Notebook - Cannot Connect to Kernel

Question

I\'ve tried installing jupyter notebook using pip3 install jupyter. Every time i launch a new jupyter notebook, the notebook is unable to connect to the kernel. See screenshot b

Answer 1

I experienced a similar issue on my old PC converted into a Ubuntu 20.04 server, with Jupyterlab running under Jupyterhub. The issue appeared after installing Jupytext with the following command:

python3 -m pip install jupytext --upgrade

which non only installed Jupytext but also upgraded my system to Jupyterlab 2.2.9 and Jupyterhub 1.2.2 (among other packages updates).

After that, running a cell containing the simple code:

3 * 4

under any python 3.6 kernel or even R 3.6 or 4.0 kernel left me with the status message:

Kernel xxx connecting...

but never completing the connection nor the simple computation.

Neither re-installing Tornado to version 5.1.1., nor reinstalling ipywidgets, succeeded in solving the issue.

But finally downgrading Jupyterlab and Jupyterhub to (approximately) the original version numbers worked for me:

python3 -m pip install wheel jupyterhub==1.1.0 jupyterlab==2.1.0 ipywidgets

According to the command outputs, the following packages versions were actually applied:

Installing collected packages: wheel, jupyterhub
  Attempting uninstall: wheel
    Found existing installation: wheel 0.34.2
    Uninstalling wheel-0.34.2:
      Successfully uninstalled wheel-0.34.2
  Attempting uninstall: jupyterhub
    Found existing installation: jupyterhub 1.1.0
    Uninstalling jupyterhub-1.1.0:
      Successfully uninstalled jupyterhub-1.1.0
Successfully installed jupyterhub-1.2.2 wheel-0.36.1

And after restarting jupyterhub, all my kernels were working again.