What is a “file descriptor”, really?

People say “in UNIX, everything is a file”. And that we interact with the operating system through “file descriptors”.

I don’t find this very enlightening. All it means is that the word “file” is overloaded to mean “some sort of resource”. Here are things that a file descriptor can represent:

Depending on how you got your “file descriptor”, the operations you can do on it are different. There is no universal API for interacting with a “file descriptor”. For example, if you call kqueue() to get a new kernel queue, you should not perform a write operation on it. Just because it’s a “file descriptor”, it doesn’t mean you can write to it like that. It’s a kernel queue, which is completely different from a file.

“File descriptor” should be renamed “resource descriptor”.

I just released Vidrio, a free app for macOS and Windows to make your screen-sharing awesomely holographic. Vidrio shows your webcam video on your screen, just like a mirror. Then you just share or record your screen with Zoom, QuickTime, or any other app. Vidrio makes your presentations effortlessly engaging, showing your gestures, gazes, and expressions. #1 on Product Hunt. Available for macOS and Windows.

With Vidrio

With generic competitor

More by Jim

Tagged . All content copyright James Fisher 2016. This post is not associated with my employer. Found an error? Edit this page.