File descriptors are a crucial part of any operating system, as they provide a way for programs to access files. Each file descriptor is a small integer that is used to identify a particular file. When a program opens a file, the operating system assigns it a file descriptor. This file descriptor is then used by the program to read from or write to the file.
There are a number of ways to check file descriptors. One way is to use the `lsof` command. The `lsof` command lists all of the open files on a system, along with their file descriptors. Another way to check file descriptors is to use the `fstat` system call. The `fstat` system call returns information about a file, including its file descriptor.
