Hands-On System Programming with Linux

How the Unix permission model works

A really important point to understand regarding this topic is this: both the shared object that is being worked upon (here, the myfile file) and the process that is performing some access (rwx) on the object (here, the echo process) matter. To be more correct, their attributes with respect to permissions matter. The next discussion will help make this clear.

Let's consider this step by step:

1. A user with the login name seawolf logs in to the system.
2. On success, the system spawns a shell; the user is now at the shell prompt. (Here, we consider the traditional case of logging into a command-line interface (CLI) console, not a GUI environment.)

Every user has a record; it's stored in the /etc/passwd file. ...