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Aisalkyn Aidarova
Aisalkyn Aidarova

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This is a strong interview-preparation guide for a DevOps/SRE/Cloud Engineer role.

1. What is an Operating System (OS)?

Interview Question

What is an Operating System?

Answer

An Operating System (OS) is software that acts as an interface between users/applications and computer hardware.

Responsibilities:

  • Process management
  • Memory management
  • File system management
  • Device management
  • Security and permissions
  • Networking

Examples:

  • Linux
  • Windows
  • macOS

Real Life Example

When you open Chrome:

  1. Chrome requests CPU resources.
  2. OS allocates RAM.
  3. OS schedules CPU time.
  4. OS accesses files from disk.
  5. OS displays output on screen.

Without an OS, hardware cannot be efficiently utilized.

2. What Happens When You Type a Command in Linux?

Example 

ls
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Answer

  1. User enters command in Shell.
  2. Shell sends request to Kernel.
  3. Kernel schedules process.
  4. CPU executes instructions.
  5. Output returned to Shell.
  6. Shell displays result.

Flow:

User
 ↓
Shell
 ↓
Kernel
 ↓
CPU/RAM
 ↓
Output
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3. What is Linux?

Answer

Linux is an open-source operating system kernel.

Common distributions:

  • Ubuntu
  • CentOS
  • Red Hat
  • Amazon Linux
  • Debian

Why Linux?

  • Secure
  • Stable
  • Free
  • Highly customizable
  • Most cloud servers use Linux

4. What is a Kernel?

Answer

Kernel is the core of the operating system.

Responsibilities:

  • Process management
  • Memory management
  • Hardware communication
  • Device drivers

Example:

Chrome requests memory.

Kernel decides:

  • How much RAM
  • Which CPU core
  • What permissions

5. What is a Process?

Answer

A process is a running instance of a program.

Example:

firefox
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When Firefox starts:

  • Process ID assigned
  • Memory allocated
  • CPU assigned

Check processes:

ps -ef
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or

top
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6. What is PID?

Answer

PID = Process ID

Every running process gets a unique number.

Example:

ps -ef
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Output:

root 1234 nginx
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1234 is PID.

7. What is RAM?

Answer

RAM (Random Access Memory) is temporary memory used by running applications.

Example:

Application running:

  • Stored in RAM

Server reboot:

  • RAM contents disappear

8. Difference Between RAM and Disk

RAM Disk
Temporary Permanent
Fast Slower
Lost after reboot Survives reboot
Running programs File storage

9. What is a File System?

Answer

File System organizes files and directories on storage.

Examples:

  • ext4
  • xfs
  • NTFS

Linux stores everything as files.

10. Linux Directory Structure

Question

Explain Linux file system hierarchy.

Answer 

/
├── bin
├── etc
├── home
├── var
├── tmp
├── opt
├── usr
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Important Directories

/etc

Configuration files

/etc/nginx/nginx.conf
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/var

Logs

/var/log
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/home

User files

/home/ec2-user
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/tmp

Temporary files

/bin

System commands

ls
cp
mv
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11. What is Troubleshooting?

Answer

Troubleshooting is a systematic process of finding and fixing issues.

Steps

  1. Identify problem
  2. Collect logs
  3. Verify symptoms
  4. Find root cause
  5. Fix issue
  6. Verify fix

12. Website Not Working. How Do You Troubleshoot?

Answer

Step 1

Check DNS

nslookup google.com
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Step 2

Check connectivity

ping
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Step 3

Check port

telnet hostname 80
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Step 4

Check service

systemctl status nginx
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Step 5

Check logs

journalctl
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or

cat /var/log/nginx/error.log
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13. What is Hardware?

Answer

Physical components of a computer.

Examples:

  • CPU
  • RAM
  • SSD
  • Motherboard
  • NIC

14. What is Software?

Answer

Programs that run on hardware.

Examples:

  • Linux
  • Windows
  • Chrome
  • Docker

15. CPU vs RAM

CPU

Brain of computer.

Executes instructions.

RAM

Working memory.

Stores active data.

16. What is a Server?

Answer

A server is a computer that provides services to other computers.

Examples:

  • Web Server
  • Database Server
  • DNS Server

17. What is AWS?

Interview Question

What is AWS?

Answer

AWS stands for Amazon Web Services.

Cloud platform providing:

  • Compute
  • Storage
  • Networking
  • Databases
  • Security

Benefits:

  • Pay as you go
  • Highly available
  • Scalable

18. What is a Region?

Answer

A Region is a geographical area containing multiple Availability Zones.

Examples:

  • us-east-1
  • us-east-2
  • eu-west-1

19. What is an Availability Zone?

Answer

Availability Zone (AZ) is one or more data centers inside a region.

Example:

us-east-1
├── us-east-1a
├── us-east-1b
├── us-east-1c
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Applications are deployed across multiple AZs for high availability.

20. What is EC2?

Answer

EC2 = Elastic Compute Cloud

Virtual server in AWS.

Used to run:

  • Applications
  • Databases
  • Websites

Example:

Launch Linux EC2.

SSH into it.

Install nginx.

Host website.

21. What is EBS?

Answer

EBS = Elastic Block Store

Persistent storage attached to EC2.

Like a virtual hard drive.

Example:

EC2
  ↓
EBS Volume
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If EC2 stops:

Data remains on EBS.

22. What is S3?

Answer

S3 = Simple Storage Service

Object storage.

Stores:

  • Images
  • Videos
  • Backups
  • Logs

Example:

bucket
 ├─ image.jpg
 ├─ video.mp4
 └─ logs.txt
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Features:

  • Durable
  • Scalable
  • Cheap

23. What is ECS?

Answer

ECS = Elastic Container Service

AWS container orchestration service.

Runs Docker containers.

Components

  • Cluster
  • Task Definition
  • Service
  • Task

Flow:

Docker Image
     ↓
ECR
     ↓
ECS Task
     ↓
ECS Service
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24. What is Lambda?

Answer

AWS Lambda is serverless compute.

You upload code.

AWS runs it.

No server management required.

Example:

API Gateway
      ↓
Lambda
      ↓
S3
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25. What is API Gateway?

Answer

API Gateway exposes APIs to users.

Acts as front door for backend services.

Example:

User
 ↓
API Gateway
 ↓
Lambda
 ↓
Database
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Benefits:

  • Authentication
  • Throttling
  • Monitoring

26. How Do Two Computers Communicate?

Answer

Example:

Laptop → Google Server

Step 1

Laptop gets IP address.

Example:

192.168.1.10
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Step 2

DNS resolves domain.

google.com
↓
142.x.x.x
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Step 3

TCP connection established.

3-Way Handshake:

SYN
SYN-ACK
ACK
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Step 4

Data exchanged.

Step 5

Response returned.

27. Explain OSI Model

Answer

OSI has 7 layers.

7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
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Layer 7 Application

User applications.

Examples:

  • Chrome
  • Firefox

Protocols:

  • HTTP
  • HTTPS

Layer 6 Presentation

Encryption.

Examples:

  • SSL
  • TLS

Layer 5 Session

Maintains communication sessions.

Layer 4 Transport

Reliable communication.

Protocols:

  • TCP
  • UDP

Layer 3 Network

Routing.

Device:

  • Router

Protocol:

  • IP

Layer 2 Data Link

MAC addresses.

Device:

  • Switch

Layer 1 Physical

Cables and signals.

Examples:

  • Fiber
  • Ethernet

28. Explain TCP 3-Way Handshake

Answer

Connection establishment:

Client → SYN
Server → SYN-ACK
Client → ACK
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After this, data transfer begins.

29. What is DNS?

Answer

DNS converts domain names into IP addresses.

Example:

google.com
↓
142.250.x.x
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Command:

nslookup google.com
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30. Common Linux Commands Every DevOps Engineer Must Know 

pwd
ls -la
cd
cp
mv
rm
mkdir
find
grep
cat
less
tail
head
chmod
chown
ps
top
df -h
du -sh
free -m
netstat
ss
curl
wget
systemctl
journalctl
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These are the foundational interview questions for DevOps, Linux, Cloud, SRE, and AWS roles. A 6-year DevOps interview will often build on these basics and then move into Docker, Kubernetes, Terraform, CI/CD, VPCs, Load Balancers, Auto Scaling, IAM, monitoring, logging, and troubleshooting scenarios.

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