JupyterHub doesn't see JupyterLab

[jluttine]

Issue description

When JupyterLab has been installed with JupyterHub, the hub should have an URL of the form http://localhost:8000/user/jluttine/lab to launch JupyterLab (see https://jupyterlab.readthedocs.io/en/stable/user/jupyterhub.html). However, this doesn't seem to work for some reason although I added jupyterlab to propagatedBuildInputs of jupyterhub.

Steps to reproduce

Add jupyterlab to propagatedBuildInputs of jupyterhub. (And also notebook if you don't have it there already, see #58542.)

Launch nix shell with nix-shell -p python3Packages.jupyterhub.

Launch Jupyter Hub with jupyterhub.

Open localhost:8000in your browser and log in (with your actual Linux username and password).

Try to open URL: http://localhost:8000/user/jluttine/lab (replace jluttine with your username).

Instead of opening JupyterLab, you'll see 404 error page.

Technical details

$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 4.14.103, NixOS, 19.09.git.1233c8d (Loris)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.2`
 - nixpkgs: `/etc/nixpkgs`

[jluttine]

Turns out that the docs were a bit incorrect. The Hub needs to be launched as:

jupyterhub --Spawner.cmd='jupyter-labhub'

Then it works.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/anyone-has-a-working-jupyterhub-jupyter-lab-setup/7659/1