Why does Linux have a limit on the number of open files?

Question

linux

Linux, and probably all other Unixes (correct me if I'm wrong) have a /proc/sys/fs/file-max file that has a ceiling on the number of open files.
I have three questions:

1. Why is this needed?
   
2. How is this number chosen?
   
3. Is it possible to set different values ​​for different users?
   

Answer 1

There is a limit on the number of open files in all operating systems, including Windows. And it is needed because a descriptor is created for each open file in a special memory area of ​​the operating system kernel. This area is not unlimited, and if it is exhausted, the system can spill out into a crust . No one likes an operating system that you can fill up just by opening files and not closing them.

Answer 2

To prevent processes from opening files
Empirically
You can set limits in limits

Answer 3

This is a simple precaution and a deliberate rake for those developers who do not close file descriptors in their programs.