Linux Servers Introduction¶

Linux is the backbone of modern infrastructure and cloud computing. As a DevOps engineer, mastering Linux is essential for server management, automation, and scalable deployments.

Why Linux for DevOps?¶

Open Source: Cost-effective and customizable
Stability: Reliable for production environments
Security: Strong permission model and security features
Automation: Excellent scripting and automation capabilities
Cloud Native: Foundation for containerization and orchestration

Getting Started with Linux¶

Comprehensive Learning Resource¶

Introduction to Linux (LFS101x) | Linux Foundation

Free comprehensive course covering Linux fundamentals, perfect for beginners and those needing a refresher.

Essential Linux Concepts for DevOps¶

File System Hierarchy¶

/                    # Root directory
├── /bin            # Essential user binaries
├── /boot           # Boot loader files
├── /dev            # Device files
├── /etc            # System configuration
├── /home           # User home directories
├── /lib            # Essential shared libraries
├── /opt            # Optional software packages
├── /proc           # Process information
├── /root           # Root user home
├── /tmp            # Temporary files
├── /usr            # User programs and data
└── /var            # Variable data (logs, databases)

Key Directories for DevOps¶

Directory	Purpose	DevOps Relevance
`/etc/`	Configuration files	Service configuration, system settings
`/var/log/`	System and application logs	Monitoring and troubleshooting
`/opt/`	Third-party software	Custom application installations
`/srv/`	Service data	Web server content, databases
`/home/`	User directories	Developer workspaces, SSH keys

Essential Linux Skills for DevOps¶

1. Command Line Proficiency¶

Master these fundamental commands:

# File operations
ls, cd, pwd, mkdir, rmdir, cp, mv, rm, find, locate

# Text processing  
cat, less, head, tail, grep, sed, awk, sort, uniq, wc

# System information
ps, top, htop, df, du, free, uptime, who, id

# Network
ping, netstat, ss, curl, wget, ssh, scp, rsync

# Process management
kill, killall, nohup, screen, tmux, jobs, fg, bg

# Permissions
chmod, chown, chgrp, umask, sudo, su

2. Package Management¶

Different distributions use different package managers:

Distribution	Package Manager	Commands
Ubuntu/Debian	APT	`apt update`, `apt install`, `apt remove`
RHEL/CentOS	YUM/DNF	`yum install`, `dnf install`, `rpm -qa`
SUSE	Zypper	`zypper install`, `zypper update`
Arch Linux	Pacman	`pacman -S`, `pacman -Syu`

tldr: apt

Package manager for Debian/Ubuntu-based distributions.

sudo apt update              # Refresh package index
apt search <package>         # Search by name or description
apt show <package>           # Show package details
sudo apt install <package>   # Install or upgrade a package
sudo apt remove <package>    # Remove a package (keep config files)
sudo apt purge <package>     # Remove package and its config files
sudo apt upgrade             # Upgrade all installed packages
apt list --installed         # List all installed packages

More info: https://manned.org/apt.8

3. Service Management¶

Modern Linux uses systemd for service management:

# Service operations
systemctl start service-name
systemctl stop service-name  
systemctl restart service-name
systemctl reload service-name
systemctl enable service-name
systemctl disable service-name

# Service status
systemctl status service-name
systemctl is-active service-name
systemctl is-enabled service-name

# System operations
systemctl reboot
systemctl poweroff
systemctl suspend

tldr: systemctl

Control the systemd system and service manager.

systemctl status                             # Show all running services
systemctl status <unit>                      # Status of a specific service
systemctl start|stop|restart|reload <unit>   # Manage a service
systemctl enable|disable <unit>              # Enable/disable at boot
systemctl daemon-reload                      # Reload after unit file changes
systemctl is-active|is-enabled <unit>        # Check service state
systemctl list-units --type service --state failed  # List failed services
systemctl cat <unit>                         # Show unit file contents

More info: https://www.freedesktop.org/software/systemd/man/latest/systemctl.html

Linux Security Fundamentals¶

User and Group Management¶

# User operations
useradd username
usermod -aG groupname username
passwd username
userdel username

# Group operations  
groupadd groupname
groupmod groupname
groupdel groupname

# Permission management
chmod 755 filename        # rwxr-xr-x
chmod u+x,g+r filename    # Add execute for user, read for group
chown user:group filename # Change ownership

SSH Security¶

tldr: ssh

Securely connect to and execute commands on remote systems.

# Connect to a remote server
ssh <user>@<host>

# Connect with a specific private key
ssh -i ~/.ssh/my_key <user>@<host>

# Connect on a non-default port
ssh -p 2222 <user>@<host>

# Execute a remote command
ssh <user>@<host> <command>

# Local port forwarding (localhost:9999 → remote:80)
ssh -L 9999:example.com:80 -N -T <user>@<host>

# Dynamic SOCKS proxy on localhost:1080
ssh -D 1080 <user>@<host>

# Jump through a bastion host
ssh -J <user>@<bastion> <user>@<target>

More info: https://man.openbsd.org/ssh

tldr: ssh-keygen

Generate SSH keys for authentication and password-less logins.

# Generate a key interactively (prompts for file and passphrase)
ssh-keygen

# Generate a modern Ed25519 key
ssh-keygen -t ed25519 -C "comment or email"

# Generate an RSA 4096-bit key
ssh-keygen -t rsa -b 4096 -C "comment or email"

# Save key to a specific file
ssh-keygen -f ~/.ssh/my_key -t ed25519

# Change the passphrase on an existing key
ssh-keygen -f ~/.ssh/my_key -p

# Extract the public key from a private key
ssh-keygen -f ~/.ssh/my_key -y

# Remove a stale host from known_hosts
ssh-keygen -R <remote_host>

More info: https://man.openbsd.org/ssh-keygen

# Generate SSH key pair
ssh-keygen -t rsa -b 4096 -C "your-email@example.com"

# Copy public key to server
ssh-copy-id user@server

# SSH with key authentication
ssh -i ~/.ssh/private_key user@server

# SSH config file (~/.ssh/config)
Host myserver
    HostName server.example.com
    User myuser
    Port 2222
    IdentityFile ~/.ssh/my_key

Next Learning Steps¶

After mastering Linux basics, explore:

Practical Exercises¶

Hands-on Learning

Set up a Linux VM or cloud instance
Practice command line operations daily
Configure SSH key authentication
Explore system logs in /var/log/
Set up a basic web server

Production Considerations

Always test commands in development first
Use configuration management tools for consistency
Implement proper backup strategies
Follow the principle of least privilege
Keep systems updated and patched

DevOps Integration¶

Linux skills directly enable:

Infrastructure as Code: Ansible, Terraform automation
Containerization: Docker and Kubernetes deployments
CI/CD Pipelines: Build agents and deployment scripts
Monitoring: Log analysis and system monitoring
Cloud Operations: EC2, VPS, and bare metal management