What are file watchers in an Angular app, and how to clean them up? (System limit for number of file watchers reached)

Question

I have a simple Angular app, that is a collection of small example apps.
(The code can be found on GitHub, and the homepage is here.)

I work on it locally. Suddenly the following error is all over my console, when I do ng serve:

Watchpack Error (watcher): Error: ENOSPC:
System limit for number of file watchers reached,
watch '/home/tilman/Code/angular_examples/node_modules/blah/blah'

But the app still works. There seems to be no problem, except my flooded console.

Some details:
   Ubuntu 20.04
   PyCharm 2024.1.3 (Professional Edition)
   Angular CLI: 13.3.4
   Node: 17.9.0 (Unsupported, according to ng v)
   Package Manager: npm 8.5.5
   /proc/sys/fs/inotify/max_user_watches: 65536

Similar questions have been asked about React in 2019 and about Angular in 2021.
The answers mostly sound like: Pressing some buttons worked for me.
But I would like to know what is going on here.

I was not aware, that file watchers are a thing.
Do I need them? Where are they? Why are there so many? How to clean them up?

One of the proposed solutions is deleting and reinstalling node_modules.
That is not a good way to solve problems. (What if something is gone, when I try to reinstall it?)

One answer to the React question sounds quite reasonable:
add watchOptions: { ignored: /node_modules/ } to webpack.config.js
I just don't have that file.

Initially the errors are for all kinds of folders in node_modules.
Eventually only these four are repeated in a loop:

/home/tilman/Code/angular_examples/node_modules/jquery/dist
/home/tilman/Code/angular_examples/node_modules/jquery
/home/tilman/Code/angular_examples/node_modules/typescript/lib
/home/tilman/Code/angular_examples/node_modules/typescript

Here is a screenshot, showing Compiled successfully among the error messages:

---

Edit: A popup in Pycharm sends me to this support page: Inotify Watches Limit (Linux)
There I am told, that I should just increase the number of allowed watchers.
A user asks about the same problem, also in an Angular project.
The answer is, that folders can not be excluded from watching.
But there is a proposal that users can vote for: https://youtrack.jetbrains.com/issue/IJPL-2175

Anyway, I have added node_modules to the excluded folders, and now the problem is gone. (It was already orange, but ulike dist and tmp it did not appear in the list.)

Answer 1

The solution is of course not to watch files in node_modules.
(Because nothing there is supposed to be changed.)

I have added it to the excluded folders in Pycharm. Apparently that worked.
(See screenshot at the end of the question.)