practical Linux knowledge map for a DevOps engineer

1. Linux Basics (Must-Know)

You use this every day

• File system structure: /, /etc, /var, /opt, /home, /tmp
• Absolute vs relative paths

• Basic commands:

  • ls, cd, pwd, cp, mv, rm, mkdir, touch
  • cat, less, head, tail

• File permissions:

  • chmod, chown
  • Read/write/execute (rwx)

• Users & groups:

  • useradd, userdel, groupadd
  • /etc/passwd, /etc/group
  • sudo, /etc/sudoers

Interview focus:
“How do you restrict access to files?”
“How do you give sudo access safely?”

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2. Process & Resource Management

How Linux runs applications

• Processes:

  • ps, top, htop
  • kill, kill -9

• System load & resources:

  • CPU, memory, swap
  • free -m, uptime, vmstat

• Background & foreground:

  • &, jobs, bg, fg, nohup

Real-world usage:
Killing stuck services, finding memory leaks, CPU spikes.

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3. Networking (Very Important for DevOps)

• Network basics:

  • IP, ports, DNS, routing

• Commands:

  • ip a, ip r
  • ss, netstat
  • ping, traceroute
  • curl, wget

• Firewalls:

  • ufw, iptables

• Port troubleshooting:

  • lsof -i :8080

Interview focus:
“Service is up but not reachable — what do you check?”

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4. Disk & Storage

Used heavily in cloud

• Disk commands:

  • lsblk, df -h, du -sh

• Mounting:

  • mount, umount
  • /etc/fstab

• Partitions:

  • fdisk, parted

• Filesystems:

  • ext4, xfs

• LVM (important):

  • pvcreate, vgcreate, lvcreate
  • Resize volumes safely

AWS relevance:
EBS volumes, resizing disks without downtime.

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5. Logs & Troubleshooting

One of the most critical DevOps skills

• Log locations:

  • /var/log/syslog
  • /var/log/messages
  • /var/log/auth.log

• journalctl:

  • journalctl -u nginx
  • journalctl --since today

• Application logs vs system logs

Interview focus:
“How do you debug a failed service?”

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6. Services & Systemd

How applications start

• Service management:

  • systemctl start|stop|restart
  • systemctl status
  • systemctl enable

• Service files:

  • /etc/systemd/system/*.service

• Startup behavior

Real-world:
Restarting apps, debugging startup failures.

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7. Package Management

• Ubuntu/Debian:

  • apt, apt-get

• RedHat/CentOS:

  • yum, dnf

• Install, update, remove packages

• Repositories

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8. Shell & Bash (Core DevOps Skill)

Automation starts here

• Bash basics:

  • Variables, environment variables
  • $PATH

• Redirection & pipes:

  • >, >>, <, |

• Text processing:

  • grep, awk, sed, cut, sort, uniq, wc

• Scripts:

  • if, for, while
  • Functions

• Cron jobs:

  • crontab -e

Interview focus:
“How do you automate repetitive tasks?”

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9. SSH & Security

• SSH:

  • ssh, scp, rsync
  • SSH keys (id_rsa, authorized_keys)

• Permissions & security basics

• Firewall rules

• Fail2ban basics

• SELinux (basic awareness)

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10. Containers & Linux

Docker and Kubernetes depend on Linux

• Namespaces & cgroups (concept)
• File permissions inside containers
• Volume mounts
• Networking inside containers

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11. Monitoring & Performance

• Tools:

  • top, htop, iotop
  • sar, dstat

• Disk I/O vs CPU vs Memory issues

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What Companies Expect (Summary)

A DevOps engineer must be able to:

• SSH into servers
• Debug issues using logs
• Manage services
• Handle disks and networking
• Write Bash scripts
• Secure access
• Support Docker/Kubernetes workloads

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DevOps Interview Reality

You are not expected to be a Linux kernel developer, but you are expected to:

• Fix broken servers
• Debug production issues
• Automate tasks
• Understand what Linux is doing under the hood