Module · DevOps Engineer
Security & Hardening
Least privilege, secret hygiene and hardened defaults for every machine you touch.
TOPIC 01
Secrets & Credentials
Where credentials live, how they must be protected, and how to keep them out of Git history.
What you'll practice
- Keep a Credentials File Private — guided · beginner
- Rotate a Leaked Credential — practice · intermediate
A command you'll meet
chmod 600 ~/app/.envPermissions are the cheapest security control you have. Open the task below for the full walkthrough.
Hands-On Tasks in This Topic (2)
Keep a Credentials File Private
Application secrets belong in one file with owner-only permissions. Create ~/app/.env with an API key and lock it down to mode 600 so no other account on the machine can read it.
Rotate a Leaked Credential
A key that leaked is a key you rotate, not one you delete. Issue a replacement credential, protect it like the original, and leave a trail that proves the rotation happened.
TOPIC 02
Access Control & Least Privilege
Lock down remote access, keep administrative privileges narrow, and make audits repeatable.
What you'll practice
- Harden the SSH Daemon — practice · intermediate
- Write a Reusable Audit Script — challenge · intermediate
A command you'll meet
ss -tlnpEvery service that listens is a door. Open the task below for the full walkthrough.
Hands-On Tasks in This Topic (2)
Harden the SSH Daemon
Password logins and root logins are the two most abused doors into a Linux box. Write an sshd_config that closes both and trims the attack surface further.
Write a Reusable Audit Script
Audits should be repeatable, not remembered. Write a script that lists the listening sockets, counts the failed requests in the access log and is readable only by its owner.
TOPIC 03
Auditing & Evidence
Turn raw logs into findings someone can act on - with numbers attached to names.
What you'll practice
- Find the Noisy Client in the Access Log — scenario · advanced
A command you'll meet
grep 500 /var/log/app/access.logAn audit trail is only useful if it ends in a finding. Open the task below for the full walkthrough.