Linux administration and shell scripting
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Your app can't connect to the database. Latency is spiking. DNS resolution is failing. A microservice can't reach its dependency. Networking issues are behind the majority of production incidents, and if you can't debug them from the command line, you're flying blind. Let's fix that.
A new developer joins your team on Monday. They need SSH access to three servers, permission to deploy to staging, read-only access to production logs, and sudo for a handful of commands. Do you give them full root access and hope for the best? Absolutely not. Here's how to do it right.
Two containers are running on the same machine. One is your API server, the other is your database. They need to talk to each other. But how? They are isolated processes — they do not share localhost. Understanding Docker networking is the difference between containers that communicate effortlessly and hours of debugging "connection refused" errors.
You just got a new job. Half the servers run Ubuntu, the other half run CentOS. Your Ansible playbooks need to work on both. Your Dockerfiles target different base images. Which package manager do you use? What are the actual differences? Let's clear this up once and for all.
It's 3 AM. Your pager goes off. The production server is crawling. CPU is at 100%. Memory is gone. Something is eating your server alive, and you need to find it and stop it — fast. Knowing how to manage Linux processes isn't optional for a DevOps engineer; it's survival.
Your deployment script fails at 2 AM with Permission denied. The container can't write to the log directory. A junior developer accidentally made a config file world-writable. Sound familiar? Understanding Linux file permissions is the difference between a secure, working system and a nightmare.