Write a C Program Without a main() Function
by Başar Subaşı
Produce a valid ELF binary that runs and exits cleanly, but does not define a main() function.
Challenges
Focused hands-on problems designed to help you hone your DevOps or Server Side skills. Some challenges are more educational, while others are based on real-world scenarios. The platform provides hints and feedback for each challenge, including automated solution checks.
Reach a Remote Loopback Port Through an SSH Jump Host
An inventory service lives inside a private VPC and keeps its debugging port bound to 127.0.0.1. Use SSH local port forwarding with a jump-only bastion to query the debugging port from your workstation.
Submissions: 65/96
Reach Internal Servers Through a "No Shell" SSH Bastion
The application fleet lives inside a private VPC, reachable only through a locked-down bastion that refuses to give you a shell. Find a way to jump through the bastion and place a maintenance lock on two misbehaving servers.
Reach a Private VPC Service Through an SSH Bastion
A production search cluster lives inside a private VPC and is reachable only from within it. Use SSH local port forwarding through a public-facing bastion host to query the cluster's API from your dev machine.
Submissions: 74/94
Expose a Local Service Through an SSH Reverse Tunnel
A payment webhook receiver runs as a local build on your dev machine, bound to 127.0.0.1 and invisible from the Internet. Use SSH remote port forwarding to publish it on a public-facing gateway VM so a test payment provider can reach it.
Submissions: 48/96
Expose a Home Network Device Through an SSH Reverse Tunnel
A status dashboard runs on an isolated device in your home network, with no inbound route from the Internet. Use SSH remote port forwarding with your workstation as a jump host to publish it on a public-facing gateway VM.
Submissions: 44/51
Expose a Whole Home Network Through an SSH Reverse SOCKS Proxy
Several self-hosted services run on isolated devices in your home network, with no inbound route from the Internet. Use SSH dynamic remote port forwarding to turn a public-facing gateway VM into a single SOCKS proxy that reaches all of them.
Submissions: 38/50
Reach a Whole VPC Through an SSH SOCKS Proxy
Several internal microservices live inside a private VPC and are reachable only from within it. Use SSH dynamic local port forwarding to turn your dev machine into a single SOCKS proxy that reaches all of them through one bastion host.
Submissions: 43/50
Resolve a Port Conflict and Keep All Dev Services Running
A new service needs to run in your development environment, but the port it requires is already in use by another app that has to keep working. Diagnose the conflict, free the port without taking the other app down, and get both services running side by side - a realistic exercise in untangling local port conflicts.
Restrict Access to a Unix Domain Socket
A daemon exposes a Unix domain socket that every local user can talk to. Protect it so that only root and members of a dedicated group may connect - the same way Docker restricts access to /var/run/docker.sock.
Submissions: 46/68