EN_Linux - somaz94/DevOps-Engineer GitHub Wiki

Linux System Administration Guide

A summary of Linux concepts for DevOps engineers. Click each link for full details.


Glossary

Linux Kernel & Architecture

  • Monolithic Kernel: Kernel structure where filesystem, drivers, and memory management are compiled into a single binary (Linux)
  • Kernel Space / User Space: Memory area where the kernel runs (direct hardware access) / restricted area for user applications
  • System Call: Interface for user-space apps to request kernel services (open, read, write, fork)

Shell & CLI

  • bash / zsh / sh: Most widely used shell / enhanced autocomplete and plugins / POSIX standard
  • TTY: Physical or virtual terminal device

Filesystem

  • ext4: Default Linux journaling filesystem
  • XFS: High-performance filesystem optimized for large files
  • inode: Data structure storing file metadata (permissions, owner, size, timestamps)
  • fstab: Auto-mount configuration at boot (/etc/fstab)

Package Management

  • APT: Debian-based package management (apt install / apt update)
  • DNF/YUM: Red Hat-based package management (dnf install / yum install)
  • RPM / DEB: Red Hat / Debian package formats

Process Management

  • PID / PPID: Unique process number / parent process number
  • Daemon: Process running in the background (sshd, httpd)
  • Zombie / Orphan: Process that exited but parent hasn't collected / process whose parent exited first
  • Nice Value: Process scheduling priority (-20 to 19, lower = higher priority)

Users & Permissions

  • /etc/passwd / /etc/shadow: User account info / encrypted password storage
  • chmod / chown / umask: Change file permissions / change owner / default permission mask for new files
  • sudo / sudoers: Run commands as root / sudo permission configuration

Init System & Service Management

  • systemd: Init system and service manager in modern Linux distributions
  • systemctl: Command to control systemd services
  • Unit: Entity managed by systemd (Service, Socket, Timer, etc.)
  • Target: systemd's equivalent of runlevels (multi-user.target, graphical.target)

Security

  • SELinux: Mandatory Access Control (MAC) security module for Red Hat-based systems
  • AppArmor: MAC security framework for Debian/Ubuntu systems
  • firewalld / UFW: Dynamic firewall wrapping iptables (RHEL) / simple firewall tool (Ubuntu)

Network Management

  • ip / ss: Network interface and routing tool (iproute2) / socket statistics (replaces netstat)
  • nmcli: NetworkManager CLI tool
  • /etc/hosts / /etc/resolv.conf: Static hostname mapping / DNS configuration

Q&A List

Q1-Q3: Linux Basics & Distribution Comparison

Covers what Linux is and its key components, differences between Red Hat-based (RHEL, CentOS, Fedora) and Debian-based (Ubuntu, Debian) distributions in terms of package management, service management, and directory structure.

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Q4-Q6: System Administration

Covers Linux system management commands, essential CLI tools (ls, grep, awk, sed, find), user management with /etc/skel, and key configuration files for managing users and services.

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Q7: Linux Kernel

Covers the Linux kernel architecture, kernel modules, kernel updates and version management, and key kernel-related concepts for system engineers.

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Reference

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