How does Linux know what program to open files with?

Answer 1

The exact method the desktop environment uses (it is not a feature of the Linux kernel itself) that selects a program to open a file with varies slightly, but works something like this:

1. The file manager / explorer tries to identify what type of file it is. Unlike in Windows, this is not determined by the file extension, but by various identifying features in the file, such as "magic numbers", or commonly used strings, and syntax used in specific types of plaintext documents.

2. The file is matched by its type to a program.

3. The file manager launches the program with the path to the file as an input parameter, much like entering "programname filename" on the command line.