SadServers Linux & DevOps Troubleshooting Scenarios

Linux & Bash

- Linux commands, Bash scripting
- Systemd
- Networking, DNS
- Storage
- SSH, Firewall
- Libraries
- Cron and more...

Web Servers

- Nginx
- Apache
- HAProxy
- Caddy
- Gunicorn
- uWSGI
- HTTPS/TLS

Databases

- PostgreSQL
- MySQL
- SQLite
- Redis
- ClickHouse
- MongoDB
- etcd

Data Processing

- CSV
- JSON
- SQL queries

Docker

- Building images
- Multi-stage builds
- Volumes
- Networks
- Docker Compose
- Podman

Kubernetes

- kubectl
- Helm
- K8S Roles & Permissions
- Services
- Namespaces
- Deployments, StatefulSets
- ConfigMaps, Secrets

Tooling / Applications

- Git
- Rabbitmq
- Envoy
- Vault
- Harbor
- Prometheus
- Jenkins

Hacking

- Capture the Flag (CTF) Challenges
- Code Vulnerabilities
- Privilege Escalation

Languages

- Python
- Golang
- PHP
- Java
- Node.js
- C

advent2025 apache bash c caddy clickhouse cron csv data processing disk volumes dns docker envoy etcd git golang gunicorn hack haproxy harbor hashicorp vault helm java jenkins json kubernetes linux-other mongodb mysql nginx node.js php podman postgres prometheus python rabbitmq redis sql sqlite ssh ssl supervisord systemd traefik

realistic / interviews new pro business

Easy

#	Name	Time	Type
1	"Valladolid": Cleaner not cleaning	20 m	Fix New	"Valladolid": Cleaner not cleaning Scenario: "Valladolid": Cleaner not cleaning Level: Easy Type: Fix Access: Email Description: The systemd service log-cleaner.service is supposed to be run manually (not a timer or cron job) and delete log files older than 7 days in the /var/log/app directory. The service runs successfully (exit code 0), but no logs are ever deleted. Fix the service and/or the script so that old_data.log (older than 7 days) is deleted, but recent_data.log is preserved. If you accidentally delete the wrong files while debugging, run `~/reset_logs.sh` to restore them. Test: Running `sudo systemctl restart log-cleaner` deletes the file /var/log/app/old_data.log but not /var/log/app/recent_data.log The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute. Time to Solve: 20 minutes.

Medium

#	Name	Time	Type
1	Amsterdam: Cron Hijack	15 m	Hack New	Amsterdam: Cron Hijack Scenario: Amsterdam: Cron Hijack Level: Medium Type: Hack Access: Email Description: You are logged in as the user admin. A cron job (not a systemd timer) appears to be running as root every minute, related to a health check. We've discovered this set up may be insecure. Your mission is to find the running cron job, analyze it for a vulnerability, and exploit it to read the secret file at /root/secret.txt Save the secret string from the secret file to the file /home/admin/solution.txt. Test: `cat /home/admin/solution.txt` displays the same string that is in /root/secret.txt, with `md5sum /home/admin/solution.txt` returning `c6ef5d3ea5e937ae56f8635f91cc727a` (the solution string without an ending newline is also accepted) The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute. Time to Solve: 15 minutes.

Hard

#	Name	Time	Type
1	"Madrid": exploiting capabilities	20 m	Hack New	"Madrid": exploiting capabilities Scenario: "Madrid": exploiting capabilities Level: Hard Type: Hack Access: Email Description: You are logged in as the admin user without sudo privileges. A secret string is in the file /root/flag.txt and you don't have permission to read it directly. However, a standard system binary has been misconfigured with a "hidden" capability that allows it to bypass file permissions. Your mission is to find the misconfigured binary and use it to copy the content of /root/flag.txt into the file /home/admin/flag.txt. Test: `cat /home/admin/flag.txt` displays the same string that is in /root/flag.txt, with `md5sum /home/admin/flag.txt` returning `a43d338b0fc1dfb0c6425aa55e24c8c6` (the solution string without an ending newline is also accepted) The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute. Time to Solve: 20 minutes.