1.What is a file descriptor in Linux? What are standard files? What are their descriptors?

A file descriptor in Linux is a unique integer that identifies an open file or I/O stream. It is used by the operating system to keep track of open files and their associated data.

Standard files are the input, output, and error streams that are automatically opened for every process in Linux. They are referred to as standard input (stdin), standard output (stdout), and standard error (stderr), respectively.

Their descriptors are:

- 0 (stdin): the file descriptor for standard input
- 1 (stdout): the file descriptor for standard output
- 2 (stderr): the file descriptor for standard error

These descriptors are used by programs to read input from the user, write output to the terminal, and report errors to the user. They can be redirected to different files or devices using shell commands or program options.