How do linux file descriptor limits work?

Question

I was told that my server refused to accept client network connections at a specific port could be due to the lack of file descriptors. I looked up what this is all about an

Answer 1

It does not look like you are hitting the system file desriptor limit. See this answer.

Perhaps your server process uses select and is thus limited to 1024 descriptors? If you switch to another mechanism, e.g. poll you will not be limited to 1024 descriptors anymore.

select() works with fd_sets

This is from the POSIX documentation of select.h:

The following shall be defined as a macro:

FD_SETSIZE

Maximum number of file descriptors in an fd_set structure.

Try to find or output FD_SETSIZE on your system.

If you find FD_SETSIZE is too low for you, I would rather try to move away from select than trying to increase FD_SETSIZE which is typically harder.