How to limit the capacity of a folder on the server?

Question

linux

The logic of the program is as follows.
When you run a php script, it in turn launches the .sh script for execution.
Files are downloaded to a certain folder.
It is not known in advance how many files.
You need to somehow set a limit on downloading files to a folder, i.e. when the folder is full, then .sh should be chopped off by itself.
Let's say the folder capacity is 5 MB and no more.
How to do this using Linux?
Many scripts and folders can work at the same time, so controlling everything through PHP is resource-intensive + there is no pointer to stop the script.

Answer 1

After each jump in the sh script, check the size of the folder (du -s) and if it exceeds, exit. If the files are small, then the error due to multithreading will not be very large.

Answer 2

If you can divide into different owners, then look towards disk quotas.