What does the setuid permission do - CompTIA Linux + XK0-005

Question

What does the setuid permission do?

Answers

Allows directory execution
Grants execute to owner
correct

Runs file with owner’s privileges
Changes file group

Explanation

The Correct Answer is: C. Runs file with owner’s privileges
The setuid (Set User ID) permission allows a user to execute a file with the permissions of the file’s owner, rather than with the permissions of the user who ran it. This is commonly used for programs that need elevated privileges to perform specific tasks, such as passwd, which changes user passwords but must write to system files owned by root.

Why the other options are incorrect:

A. Allows directory execution
This is related to the execute (x) permission on directories, not to the setuid bit. Execute permission on a directory allows a user to access files within it by name, but it doesn’t involve running files with different privileges or altering ownership behavior.
B. Grants execute to owner
This describes the standard execute permission (x) for the owner, not the function of setuid. Setuid doesn’t grant execute permission; instead, it changes how the execution behaves—by giving the executing user the file owner's privileges during that session.
D. Changes file group
Changing a file’s group is done with the chgrp or chown command and relates to ownership, not to execution behavior. This has nothing to do with setuid, which impacts user permissions during execution, not ownership changes. Setuid doesn't affect group settings.