About IT Interviews - Part Three: A Map of Preparation Materials

In part three I share what I promised: a map of the materials I used to prepare for interviews for a Linux engineer position at the Middle+ level. Topics, articles, cheat sheets, videos and channels, plus the order in which it is best to study all this 🐧.

Also see: part one and part two.

Preface

Originally I planned to fit everything into one article, but there turned out to be too much material. So the topic was split into two parts:

• Part three (this one) - a map of materials. What to learn, in what order, and where to read or watch about it;
• Part four - a full cheat sheet: topics, typical questions and concise answers to them.

In its raw form my notes looked like a dump: summaries, links, chats with ChatGPT, videos. Your eyes wander. So here I organized everything into blocks, from general to specific. Each block comes with my blog articles, external materials and videos.

How to Use the Map

I divided the blocks below into four groups by how often they come up in interviews. This is my subjective impression from past technical interviews, the picture may differ in your market:

• Must know - asked almost always, regardless of the job title;
• Often - asked if it is in the stack or in the job description;
• Depends on the job - worth looking at only if it is mentioned in the requirements;
• Optional - not the basis of preparation, but useful for work.

The order is the same as in my preparation plan: first the foundation (Linux, networking, Bash), then the tools built on top of it (Git, Docker, Ansible, Kubernetes), and finally adjacent areas.

The Main Source of Questions

Most of my questions come from the open repository Swfuse/devops-interview, where a kind person collected all the topics they ran into themselves, plus what readers sent them. The file interview.md is a huge list of questions and answers, about 7,500 lines, with the following sections: hardware and IPMI, Linux, disks and file systems, Debug, Docker, networking, Ansible, DBMS, Python, Kubernetes, GitLab CI/CD, AWS, Git, Terraform and workflow.

There is no point in studying it from start to end, but as a question bank (just “the bank” below) for self-checking it is good. Note that the questions there are not sorted by priority and sometimes repeat. The answers should also be read critically: some are outdated, some are superficial.

I used the file like this: I read a question, try to answer, then check. If my answer was muddled, the topic goes to the review list. This very list will form the basis of part four.

In the blocks below I gave links to specific sections and questions from this file, so you do not have to search for them manually.

1. Linux: System and Command Line

Must know. The core of any such interview. As I wrote in part two, one of the interviews asked only about Linux, both in practice and in theory.

What the block includes: command line, directory hierarchy, boot process (BIOS and UEFI, bootloader, kernel, initramfs, PID 1), systemd and its units, processes and threads, signals, access rights, memory and swap, load average, system calls.

My Articles: the Command Line Series

This is my series for those who master the console from scratch, but it is also great for reviewing the basics. It is better to go through it in order:

• Introduction: types of commands, plain text, file system, shell prompt;
• Navigating the system and viewing directories: pwd, ls, cd;
• Output and reading contents: echo, cat, less;
• Working with files: touch, mkdir, cp, mv, rm;
• File links: ln;
• Input and output redirection: >, <, |;
• Command execution control: &&, ||, ;, &;
• Processes: jobs, fg, bg, ps, pgrep, kill, pkill, htop;
• File permissions: id, chmod, chown;
• Privilege escalation: su, sudo;
• Archiving and compression: tar, gzip, bzip2, xz, zstd, zip, 7z, rar.

My Articles: Breakdowns and Theory

• Breaking down the output of the top utility - it was analyzed item by item at a technical interview, a must-read;
• Initial Linux server setup using Debian as an example;
• Init system;
• A little about shebang in Linux.

Videos

They explain well how everything works under the hood (more about the channels at the end):

• How computer memory works;
• How the processor works;
• How the processor cache works;
• How the stack works;
• How the ELF file is structured (Linux);
• History of Unix. Part one: AT&T Unix and part two: BSD Unix.

Self-Check Questions

The Linux section from the main question bank. It collects questions about booting, processes, memory and permissions:

• The OS boot process from pressing the power button;
• Processes with PID 0 and 1;
• Kernel, initramfs, bootloader;
• systemd and init: what is the difference;
• PXE and network boot;
• Userspace and kernelspace;
• System calls;
• Process and thread;
• Zombie processes;
• Signals;
• SIGTERM and SIGKILL;
• Swap;
• How sudo works;
• suid, sgid and sticky bit.

Troubleshooting and Performance

A typical task: “the server is slow, what do you do?” My map had no separate block for it, so I collected the questions here. The whole Debug section is useful, plus questions from the Linux section:

• The web server returns a 502 error;
• The no such file or directory error when running a file;
• Where a program looks for its config;
• A binary crashes right at startup;
• The server is slow under load;
• available and free in the free output;
• How to check the disk load;
• Load average 900: is it normal;
• What load average shows;
• iowait: where it comes from;
• The too many open files error;
• OOM killer;
• Where to look at a service’s output;
• Breaking down the top output.

The bank has no questions about SELinux, AppArmor and PAM. If these technologies are in the job description, see the documentation of your distribution.

Might Be Useful

As an example on the PXE topic, from my articles: netboot.xyz - installing Linux online from a USB flash drive.

2. Disks and File Systems

Must know. The disk space task from part two came from this topic.

What the block includes: inode and the reasons they run out, hard and symbolic links, ext4 and xfs, /etc/fstab and mounting, LVM, RAID, the “df and du show different values” situation.

My articles on the topic:

• Linux command line, file links: ln.

Videos:

• File and directory structure in Linux;
• How a file system works (FAT-32) by Alek OS.

Self-Check Questions

The Disks and file system section of the question bank covers almost the whole block:

• What a file system is;
• What an inode is;
• Where inodes are physically stored;
• Why inodes run out and what it leads to;
• Where file and directory names are stored;
• Hard and symbolic links;
• Mounting file systems;
• /etc/fstab, /etc/mtab, /etc/mdadm/mdadm.conf;
• ext4 or xfs;
• File system problems and recovery;
• How to find the physical disk by partition;
• Which processes use a partition;
• What RAID is and what types exist;
• Tools for software RAID;
• What LVM is;
• Loop devices;
• no space left on device: causes;
• df and du show different values;
• no space left on device with free space available (quotas).

The LVM answer in the bank is short. Study the commands (pvcreate, vgcreate, lvcreate, lvextend) and growing a volume together with the file system (resize2fs, xfs_growfs) in man.

Might Be Useful

Not directly on topic, but related to images and disks of virtual machines:

• Preparing a qcow2 virtual machine image using Debian as an example;
• Building a cloud-init template on ZFS.

3. Networking and SSH

Must know. Networking questions are asked both at the HR stage (in a simplified form) and at the technical one.

What the block includes: TCP/IP and OSI models, addressing and subnets, ARP and VLAN, TCP and UDP, DNS, HTTP, TLS and SNI, SSH, the nftables firewall. A classic that comes up almost everywhere: “What happens when you type a website address in the browser?”

My Articles: SSH

• SSH - Secure connection to remote hosts: introduction;
• SSH - Fine-tuning the client in Linux: config file and ssh-agent;
• SSH - Port forwarding: direct and reverse tunnels;
• Forced command in SSH: running only one command without shell access;
• The sshd port does not change after editing sshd_config in Ubuntu.

My Articles: Firewall, DNS, VPN, TLS

• Basic Nftables setup in Linux using a Bash script;
• Ansible: managing the nftables firewall with the firewall role;
• Running your own Unbound DNS server and Pihole ad blocker in docker;
• Finding spies on the local network with NMAP;
• VPN - a technology for secure network communication;
• Running an OpenConnect SSL VPN server (ocserv) in docker for internal projects;
• mkcert - Valid self-signed TLS certificates in 3 commands in the Linux terminal.

Videos

• How TCP/IP works;
• How the internet works. The beginning;
• How the browser works;
• How WiFi works.

Self-Check Questions

The Networking section of the question bank:

• What happens when you type a website address in the browser;
• The TCP/IP model;
• IP address and subnet mask;
• Private and special-purpose address ranges;
• Routing table;
• ARP;
• VLAN;
• TCP and UDP;
• How TCP establishes a connection;
• How TCP maintains a connection;
• How DNS works;
• DNS record types;
• Recursive and non-recursive DNS queries;
• NAT;
• ICMP;
• traceroute;
• TTL;
• How an SSH connection is established and authentication works;
• TLS and SSL;
• How certificates work;
• SNI;
• L4 and L7 load balancers;
• HTTP response codes.

The bank has no hands-on practice with ss and tcpdump. Practice these utilities on a virtual machine.

Might Be Useful

Examples on the topic from my articles:

• A quick way to check VPN connection speed using SSH - an example of network diagnostics;
• Setting up DNS over HTTPS (DoH) on OpenWrt - a DNS example;
• Setting up an OpenConnect middle server for access to a closed perimeter - an example of access to closed infrastructure through an intermediate server;
• Secure file transfer with Nginx - an example of protected file distribution.

4. Bash and Python

Must know (Bash), often (Python). A systems engineer is almost always expected to be able to write scripts. Bash is checked both with questions and with a live task.

What the block includes: variables and exporting them, quotes, streams and redirection, special variables ($@, $!, $?, $$), set -euo pipefail, pipelines, grep, sed, awk, find, xargs.

My Articles

Where to start and what to read:

• How to learn to write Bash scripts: recommended materials;
• A collection of Bash one-liners;
• A collection of Bash snippets.

Breakdowns of specific techniques:

• Bash: Features of arithmetic operations - increment ((expression++));
• Bash: An example of optimizing filtering commands with grep and awk;
• Bash: Generating configs with envsubst, here document and here string;
• flock - locks in shell scripts;
• Setting up output logging for Bash scripts.

Complete scripts that are good for practice:

• Bash: Writing a universal host availability check script;
• Writing a Bash script for backups with tar;
• Writing a bash script to connect to an OpenConnect VPN server;
• About a backup script in Python.

Python is simpler: the basics are enough (data types, functions, working with files, exceptions, virtual environments, main libraries) and the ability to read someone else’s script and explain what it does.

Self-Check Questions

Bash, the Linux section:

• export VAR and VAR without export;
• Special variables $@, $!, $?, $$;
• How to output only stderr;
• How to pass stderr through a pipeline too;
• Single and double quotes;
• What the variable a equals after a pipeline.

Python, the Python section:

• Hash table;
• Generator and iterator;
• Tuple and list;
• Decorator;
• The value of a variable with no value.

Might Be Useful

From my articles, about a convenient working environment:

• ZSH - An interactive command shell for Linux + Oh-My-Zsh;
• VIM - Console editor: an introduction;
• Terminal multiplexer;
• Tmux - installation and customization + Nord theme.

5. Git

Often. The questions are usually simple, but people like to fail on them: merge and rebase, reset and revert, fetch and pull, checkout, switch and restore. Plus stash, cherry-pick and working with conflicts.

• Git commands cheat sheet - a third-party material (original on GitHub);
• Video: Git. A big practical episode.

Self-Check Questions

The Git section of the question bank:

• merge and rebase;
• When to use merge and when rebase;
• git pull and git fetch;
• cherry-pick;
• Git workflows, forks;
• GitFlow.

The bank has no questions about reset, revert and stash. You can take them from the cheat sheet above.

6. Docker and Containers

Often. Here they check not the ability to write docker run, but the understanding of what everything rests on: namespaces, cgroups, image layers, networks, the differences between CMD and ENTRYPOINT.

My Articles

• Containerization - an OS-level virtualization technology;
• Installing Docker engine on a Linux server running Debian;
• Building a docker image of the Unbound DNS server;
• Building OpenConnect (ocserv) version 1.3 from source in Debian 12 + a docker image;
• How to find all tags of a Docker image - the skopeo utility;
• A convenient Docker lab with blackjack and a Web GUI.

Third-Party Materials

A series of articles on Habr from RUVDS. It is not new, but the basics (images, containers, networks, volumes) have not changed since then:

• Article 1;
• Article 2;
• Article 3;
• Article 4;
• Article 5;
• Article 6.

Videos

• Docker basics. A big practical episode.

Self-Check Questions

The Docker containers section of the question bank. It covers the main things: namespaces, cgroups, image layers and networks.

• Containerization and virtualization;
• What Docker is built on;
• Containers and images;
• Image storage, layers, overlayfs;
• Container isolation (namespaces);
• Why a container sees only its own processes;
• Resource limits (cgroups);
• Docker network types;
• Networking between two containers;
• CMD and ENTRYPOINT;
• ADD and COPY;
• ARG and ENV;
• How to reduce the image size;
• Which user a container runs as;
• Why you should not use latest;
• What docker-compose is for.

7. Ansible and Terraform

Often. If the job description contains the words “automation” or “IaC”, these tools will almost certainly come up.

What the block includes. Ansible: playbook, play, task, module, role, inventory, handler, template, facts, vault, idempotence. Terraform: provider, resource, state and backend, variable, output, plan, apply.

My Articles

• Configuration management system - theory;
• Ansible - a configuration management system: an introduction;
• Writing an ansible playbook for the initial setup of a Linux server;
• Ansible: managing the nftables firewall with the firewall role;
• ansible-cmdb - Structuring and visualizing ansible facts;
• Creating infrastructure in Proxmox with Terraform or OpenTofu.

Third-Party Materials

• Ansible Inventory: a complete guide - an article on Habr, very useful.

Videos

• Terraform - From Zero to Certified Professional - an ADV-IT playlist.

Self-Check Questions

Ansible, the Ansible section:

• ad hoc commands;
• Roles;
• Idempotence;
• handlers;
• pull and push models;
• Main Ansible primitives;
• Module and plugin.

Terraform, the Terraform section:

• Ansible and Terraform: what is the difference;
• Provider;
• Resource;
• tfstate;
• Locking tfstate;
• Recommendations for working with tfstate;
• Configuration drift;
• How to bring a manually created resource into code;
• lifecycle rules;
• One code for several environments.

8. Kubernetes and CI/CD

Often, and almost mandatory for jobs with “DevOps” in the title. As I wrote in part one, everyone works with Kubernetes one way or another.

What the block includes. Kubernetes: Pod, Deployment, ReplicaSet, StatefulSet, DaemonSet, Job, CronJob, Service, Ingress, ConfigMap, Secret, PV and PVC, RBAC, Control Plane architecture, kubelet, CNI and CSI. CI/CD: pipelines, runners, stages, artifacts.

There are no articles of my own on these topics on the blog yet, so here I rely on videos:

• Kubernetes from scratch - an ADV-IT playlist;
• GitLab and GitLab CI/CD for DevOps - an ADV-IT playlist;
• Jenkins in Russian - an ADV-IT playlist;
• Kubernetes - In Simple Words with a Clear Example;
• CI/CD - In simple words with a clear example;
• PRODUCTION Tools of REAL development: Kubernetes, Grafana, CI/CD, Harbor and others.

The last three are by Artem Shumeiko, more about the channel below.

Self-Check Questions

Kubernetes, the Kubernetes section:

• What Kubernetes is and what problem it solves;
• Cluster architecture;
• How a Pod is created;
• Pod and container;
• Deployment and ReplicaSet;
• StatefulSet and Deployment;
• DaemonSet;
• readiness, liveness, startup probes;
• Service types;
• Ingress;
• ConfigMap;
• Secret;
• PV and PVC;
• requests, limits and QoS;
• What happens when a memory or CPU limit is exceeded;
• RBAC;
• CRI, CSI, CNI.

GitLab CI/CD, the GitLab CI/CD section:

• Key components of GitLab CI/CD;
• before_script and after_script;
• How to avoid duplicating pipeline configuration;
• How to run tests only for a merge request;
• Ways to control job execution;
• Caching.

If the cloud is in the job description, see the Cloud (AWS) section (VPC, EC2, Security Group, S3, Route 53, EKS).

9. Databases

Often. Confident SQL and an understanding of how PostgreSQL works (or MySQL, depending on what is in the job description) are enough.

What the block includes. SQL: DDL, DML, DCL, JOIN, GROUP BY, HAVING, subqueries, constraints, indexes, transactions. PostgreSQL: architecture, WAL, MVCC, VACUUM, index types, reading EXPLAIN, roles and privileges, replication.

My Articles: the PostgreSQL Series

The “PostgreSQL Administration” series. I recommend going in order:

• Part 1 - Installing and running PostgreSQL in Docker;
• Part 2 - Working with psql and DBeaver;
• Part 3 - Architecture and MVCC;
• Part 4 - Configuring PostgreSQL.

The series is not finished yet: the next parts (including VACUUM and WAL) will come later.

Third-Party Materials

• An SQL memo/cheat sheet - an article on Habr.

Videos

The “Digitalize!” channel (more below):

• Breaking down SQL using PostgreSQL as an example - SELECT, JOIN, GROUP, HAVING, COALESCE and more;
• PostgreSQL optimization basics - schema, indexes, reading EXPLAIN, access and join methods, tuning.

Self-Check Questions

The DBMS section of the question bank. Despite the name, it also has PostgreSQL questions:

• Indexes;
• Why too many indexes are dangerous;
• ACID;
• WAL;
• Roles in PostgreSQL;
• TRUNCATE, DELETE, DROP;
• How to safely change a million rows;
• Why you should not run mysqldump on a large active database;
• Master-slave replication.

Might Be Useful

On the database topic, but not about questions: Video recommendation: an interview with Ivan Panchenko, co-founder of Postgres Pro.

10. Monitoring and Logs

Depends on the job. Here the picture depends on the stack. My map had Zabbix, Prometheus, Loki, journald, rsyslog and auditd.

My articles:

• What are monitoring systems in IT? - theory;
• System log in Linux: Syslog and Journald;
• Running a Zabbix 7 + TimescaleDB monitoring server in docker;
• Breaking down the output of the top utility.

Video: Prometheus - monitoring basics - an ADV-IT playlist.

Self-Check Questions

The question bank has nothing about Zabbix, Prometheus and Loki. General questions suit this block:

• SLO, SLA, SLI;
• Breaking down the top output;
• How to check the disk load;
• Where to look at a service’s output (journalctl).

11. Virtualization, Backups, Storage

Depends on the job. If the job involves server hardware, virtualization and data storage, this block is mandatory.

What the block includes: KVM and QEMU, libvirt, Proxmox, snapshots, LVM, RAID, rsync, tar, S3-compatible storage.

My articles:

• Creating a VM template with cloud-init in Proxmox;
• Preparing a qcow2 virtual machine image using Debian as an example;
• Installing a Debian 12 server in VirtualBox;
• Arkeep - A centralized Backup server with agents, based on Restic and Rclone;
• Rclone mount - Mounting SFTP, WebDAV, S3 network storage as a local directory in Linux;
• RustFS - Installing and setting up S3-compatible storage;
• Writing a Bash script for backups with tar.

Self-Check Questions

For server hardware and virtualization the question bank has two sections: Hardware questions and Viewing hardware information.

• IPMI;
• PXE;
• QEMU;
• KVM as a hypervisor;
• qemu-kvm;
• Virtualization and emulation;
• RAID;
• LVM;
• S3.

The bank has no questions about backups (rsync, tar, restic). My articles above cover this part.

Might Be Useful

For a home lab: Installing VirtualBox in Linux Mint 21.

12. Soft Skills and Resume

Must know. This is not technical, but you need to prepare for it too. My map had three separate lists that I thought through in advance:

• Reasons for changing jobs. The answer must be honest and without negativity about the previous employer;
• Job preferences. What interests you, how much communication with customers is acceptable (in part two I wrote how that ended), whether you are ready for on-call duty;
• Questions for the employer. The stack, the release process, how on-call is organized, how onboarding goes, what the team is like.

The last one is often underestimated. Questions for the employer show that you choose the company the same way it chooses you.

Materials:

• About IT Interviews - part one;
• About IT Interviews - part two: resume, interview stages, salary size;
• DevOps and job search in IT - an ADV-IT playlist;
• Why does it not work out in IT? - a video by Alek OS.

13. AI and Agents

Optional. The topic is hyped right now. I strongly recommend learning to work with AI and agents: it is already part of the working toolkit. But do not get stuck on it while preparing for interviews. The foundation from the blocks above matters more.

What the block includes: how large language models (LLMs) and AI agents work, cloud and local models, running agents yourself, basic logic for checking model answers.

Videos

The videos will help you get a bit into the essence of the matter:

• AI for the very small: how an LLM and an AI agent work - it is better to start with this one;
• Paid LLMs versus a local model on an everyday laptop - is the difference big?;
• Learning to think right in the age of AI. How and why to study formal logic;
• Local AI without limits: installing Hermes Agent locally on Windows/Ubuntu;
• What is OpenClaw | How to install | Free and safe on a laptop.

The first three are from the “Digitalize!” channel, the last two are from ADV-IT. More about the channels below.

Might Be Useful

From my articles, if you want to try local models and AI in the terminal:

• Ollama - local AI on your Linux PC;
• ShellGPT - an AI assistant in your Linux terminal;
• Automatic Ollama updates.

YouTube Channels

From videos I mostly took what explains the basics and how systems are built, rather than yet another review of yet another tool.

Main

• ADV-IT - full course playlists: GitLab CI/CD, Prometheus, Terraform, Kubernetes, Jenkins, job search in IT and local AI agents;
• Alek OS - how everything works under the hood: memory, processor, TCP/IP, file systems, ELF, encryption. A good base for answering “how does it work” questions;
• Digitalize! - materials about databases, primarily PostgreSQL, as well as about how LLMs and AI agents work;
• GOLDEN PLAY - the history of Unix and operating systems. For an interview it is more of a background, but it helps to understand why Linux is built the way it is.

Also Useful

• Artem Shumeiko - Kubernetes, CI/CD and development tools in simple words, with examples;
• Artem Matyashov - big practical episodes (Docker, Git, OpenVPN);
• Merion Academy;
• Prosto Devops.

For Variety

• DistroTube;
• Kirill Semaev - I included the channel here out of respect and sympathy for the author. It still has an excellent Linux foundation, although there have been no new videos for a long time;
• Aleksey Samoilov;
• Ampersand;
• LinuxShef;
• overbafer1 - only old videos about cybersecurity.

How I Studied

A few thoughts about the process itself:

• Do not try to learn everything at once. Go by blocks following the table above: first Linux and networking, then the rest. Reviewing what you already know is also needed, it is not a waste of time;
• Answer the questions out loud. In your head the answer always seems coherent, but out loud it turns out it is not;
• Check everything you can on a virtual machine: ip, ss, lsof, strace, journalctl, df, du. This is exactly what is expected in live admin tasks;
• AI is good as a trainer: ask it to pose questions on a topic and review your answers. But not as a prompter during the interview itself, I wrote about this in part two;
• Do not be afraid of an honest “I don’t remember, but I would check it like this”. It is a normal answer.

Afterword

The map turned out long, and that is fine. Learning everything is unrealistic and unnecessary: the goal is not to know every Nginx directive, but to confidently understand the fundamentals.

In the next, fourth part, I will put all this together into a full cheat sheet: topics, typical questions and short answers.

Thanks for reading. Good luck with your preparation and your search! 🐧

Used Materials

• Swfuse/devops-interview;
• cyberspacedk/Git-commands;
• An SQL memo/cheat sheet on Habr;
• Ansible Inventory: a complete guide on Habr;
• A series of articles on Docker on Habr.

👨‍💻And…

Don’t forget about our Telegram channel 📱 and chat

Or maybe you want to become a co-author? Then click here🔗

💬 All the best ✌️

That should be it. If not, check the logs 🙂