Linux Security Showdown: When Alice, Bob, and Carol Invade /project/shared

Ever wonder what happens when three users walk into a directory? No, this isn't the start of a joke—it’s your next real-world RHEL 9 project!

Today, we’ll create a secure multi-user file collaboration system using Linux permissions, ACLs, setgid, and the sticky bit—because letting users roam free is chaos, and chaos is for developers, not sysadmins.

So grab your sudo powers and let’s lock this place down.

📚 Table of Contents

• Meet the Cast


• Act 1: Forming the Cult, I Mean, Group


• Act 2: The Sacred Temple of /project/shared


• Act 3: The Trash Trap with Sticky Business


• Act 4: The ACL Tribunal


• Act 5: Testing the Drama


• Curtain Call: What Did We Learn?


• Why RealWorld Projects Matter

Meet the Cast

Alice – Project lead. Bossy. Needs full access.

Bob – The “helpful” teammate who thinks he knows more than he does.

Carol – Just here to do her job and avoid drama

Act 1: Forming the Cult, I Mean, Group

We’ll start by creating a secret club called projectteam.

Now, let’s rope in our trio:

Yes, -m gives them a home. We’re not monsters.

Act 2: The Sacred Temple of /project/shared

Create a shared space where they can collaborate—or clash.

Let’s break that down:

Only the owner (root) and projectteam can access.

The setgid (2) ensures anything created in here carries the group like a family curse.

Act 3: The Trash Trap with Sticky Business

What’s a shared space without a trash folder for your mistakes?

This folder is special:

• Everyone can drop files in.




• Only the file owner (or root) can delete them.




• Perfect for passive-aggressive document deletions.

Act 4: The ACL Tribunal

Now it’s time to set the rules of engagement.

Alice gets full control (obviously)

Bob and Carol get read/execute access. Sorry, Bob.

Act 5: Testing the Drama

Switch to each user and try to stir up trouble.

Carol? She’s fine. She’ll behave

Curtain Call: What Did We Learn?

• Setgid makes files inherit group ownership.




• Sticky bit keeps people from deleting each other’s trash.




• ACLs allow for fine-tuned control over who does what.




• Bob should not be trusted with write access. Ever.

And just like that, you’ve built a secure, real-world shared collaboration system in RHEL 9—while fending off chaos, ego, and accidental deletions.

Why RealWorld Projects Matter

Working through hands-on projects like this isn’t just fun—it’s foundational.

Real-world scenarios in RHEL 9 give you the kind of practical experience that job interviews, certification exams, and production environments expect.

You move beyond memorizing commands and start understanding how, when, and why to use them. Plus, nothing beats the confidence that comes from knowing you’ve already solved problems like the ones companies face every day.