How is the access control system for files and resources implemented in Linux?

In Linux, the file and resource access control system is based on a permission model that includes three types of users: the file owner, the group, and other users. Each has permissions for reading (r), writing (w), and executing (x).

Permissions are represented as three sets of bits, for example: rwxr-xr--, where the first three characters are the owner's rights, the next three are the group's, and the last three are others'.

In addition to standard permissions, there are extended mechanisms:

• ACL (Access Control Lists) — allow setting more fine-grained permissions for individual users and groups.
• SELinux/AppArmor — mandatory access control systems that impose additional security policies.

Permissions are managed using commands like chmod (change permissions), chown (change owner), and chgrp (change group). For example:

chmod 755 script.sh  # owner: rwx, group and others: r-x
chown user:group file.txt

Thus, file access is controlled through a combination of permissions and ownership, ensuring security and flexibility in resource management.