Is the concept of file permission only applicable when access is via shell?

Question

So in Linux we have a concept of file permission. There are three classes: user, group, and others, and there are three types of permissions: read, write, and execute.

Now consider this. You are on a remote computer, you open a web browser, you access a static site on a (Linux) server, and the browser downloads the static files such as html files and image files from the server.

In this case, you did not login to the server with a user account. So how were you able to access the html files and image files? What "user" was used? Is it the "others" user? But how?

Or does file permission only works when files are accessed via shell?

Answer 1

The web server runs in the background under a system-level user account. You're using that user's permissions in this scenario.

System users are created via mechanisms like useradd --system and generally cannot be logged into. Even so, they're legitimate "users" for the purposes of permission checking.

If you look in /etc/group, you're likely to find a group named after the particular web server you're using (nginx, apache, etc.) or something generic (e.g. wwwdata) so that you can chgrp your static files to be readable by the web server without changing their ownership.