FirstTry

Objective 2.5

XK0-005

Given a scenario, apply the appropriate access controls.

Objective 2.5 sits in Security, which carries 21% of the Linux+ exam. The questions below are original, written from the official objective title above, and each explanation cites the CompTIA page it rests on.

Objective title verbatim from the official objectives. CompTIA exam page ↗

A worked example

Shown solved, with the whole explanation open: this is what every question here carries.

2-5Security

In the four-digit mode 4755, what does the leading 4 set?

The set-user-ID bit on executionCorrect · your answerCorrect. Four in the leading digit is set-user-ID.
The set-group-ID bit on executionSet-group-ID is 2 in that digit.
The restricted deletion flag bitThe restricted deletion flag is 1 in that digit.
Read permission for the file ownerOwner read is the 4 in the second digit, not the first.

Correct.

Checked against man7.org, August 2026

Concept

The optional leading digit encodes the three special bits, each with its own value, ahead of the familiar owner, group and other digits.

Why A

The first digit combines set user ID at 4, set group ID at 2 and the sticky or restricted deletion attribute at 1, so a leading 4 sets set-user-ID.

Source

…et user ID (4) and set group ID (2) and restricted deletion or sticky (1) attributes. The second digit selects permissions for the user who owns the file: read (4), write (2), and…

chmod(1), change file mode bits, checked August 2026
#permissions#chmod

Now you: objective 2.5 questions

No account needed. The explanation opens when you answer.

Sample question 1 of 3

2-5Security

Users keep deleting each other's files in a world-writable shared directory. Which single bit stops that while leaving the directory writable?

Sample question 2 of 3

2-5Security

A script recursively applies numeric modes to a tree, and set-group-ID directories keep their bit even though the digits did not include it. Why?

Sample question 3 of 3

2-5Security

Even as root, an administrator cannot edit or delete /etc/resolv.conf, and no permission looks wrong. Which attribute most likely explains this?

Full Linux+ question bank coming

We’re writing the complete bank from the official objectives right now. Leave your email and we’ll tell you when it ships, nothing else, ever.

Read the sources

These are the official pages the questions above cite. Reading them is studying the objective from the primary source, which is what the explanations point you toward anyway.

More objectives in Security