Notes - Computer Security MT24, Access control in UNIX

@Describe how access control works in UNIX.

Each object is associated with a user, a group and an “other”
Each object has nine permission flags:
- Read (r), write (w), execute (x), (or s instead of x)
- For each user, group and other.
Each object belongs to one UID and one GID.
When a process requests access:
- If its UID matches the object’s UID, the user permissions are used
- If its GID matches the object’s GID, the group permissions are used
- Otherwise, the other permissions are used

Explain the permissions on a file where ls -l shows

drwxrws---

d means that the file is a directory
rwx means that the owner has read, write and execute permissions (executing a folder means you can navigate into it)
rws means that the group owning the file can read, write and execute. The s instead of an x means that any user (allowed) to execute it will have their GID set to the owning group.
--- means that all other users cannot read, write or execute.