01 · FoundationsLab 3 / 59
Challengelinux
Linux Security & SSH Hardening — Challenge
Lock down SSH without locking yourself out, and know how to recover when you inevitably do.
- Time
- 22 min
- Level
- Beginner
- Objectives
- 4 objectives
- Cost
- Free
Where this fits in the platform
Already built
This lab adds
- Key-only SSH access, root login disabled
Before you start
You will need
- A Linux host you can reach another way (console, snapshot, or a second VM)
You do not need these already — the lab environment below provides them.
You will be able to
- Move from password login to key-only authentication safely
- Grant administrative access without handing out root
- Verify a change from a second session before trusting it
Cost — Free
— a VM, a container, or a spare machine.
The goal#
Achieve the same outcome as Linux Security & SSH Hardening, from an empty starting point, without the steps.
A server is reachable on port 22 with password authentication and a shared root login. It is being scanned within minutes of being created — that is not paranoia, it is what the auth log shows.
This lab closes it down. The order matters more than the settings: get it wrong and you lock yourself out of a machine you cannot physically reach.
Hands-on environment
Run this lab in a real terminal, free and in your browser. The environment is temporary and yours alone — break it as much as you like.
Start the challengeOpens in Killercoda, in a new tab — keep this page open for the steps.
This is the guided lab's environment — the same machine, with its walkthrough on the left. Work from the task above and leave those steps alone until you are done, or you are reading the answers.
Run it on your own machine
Run this lab on your own machine. One command starts the environment, with everything the lab needs already installed:
You will need:
- bash
git clone https://github.com/EgyKode/EgyKode-lab.git
cd EgyKode-lab
./egykode start
./egykode shellYou need Docker and Git installed. Everything else runs inside the environment. The first start downloads it and takes a few minutes; later starts are seconds.
Not sure what you already have? Run: npm run doctor — it checks and changes nothing.
Anything you tick here is your own record. EgyKode cannot see inside that terminal, so the success criteria stay self-assessed even when the environment checks your work for you.
What must be true when you are done
Step 1 of 3
What must be true when you are done#
- Key-based login works for a non-root administrative user.
- Password authentication and direct root login are both refused.
- You proved the new configuration in a second session before closing the first.
- A firewall permits SSH and nothing else you did not intend.
Rules#
- Do not open the guided lab until you are finished, or until the same problem has held you up for 20 minutes.
- Documentation is allowed and encouraged.
- Verify every criterion with a command whose output you can read.
If you get stuck#
- What did you expect, exactly?
- What happened instead — the error text, not a paraphrase?
- Which layer is that error from?
- What is the smallest command that proves the layer below is fine?
You are done when
0 of 4
The concept behind it
Next up
Lab 3 of 59 on the project path