Documentație3.1.4. Rights Management
Unix-like systems support multiple users and groups and allow control of permissions. Most of the time, a process is identified by the user who started it. That process is only permitted to take actions permitted for its owner. For instance, opening a file requires the kernel to check the process identity against access permissions (for more details on this particular example, see section 3.4.4, “Managing Rights” [pagina 57]).