Operating Systems

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What Is an Operating System?

What Happens When You Run a Program

Setting Up Your Environment

C Survival Guide for Operating Systems

Essential System Tools

Interview Questions

How the CPU Executes Instructions

Privilege Levels: User Mode and Kernel Mode

The Memory Hierarchy and Why Latency Matters

Interrupts, Exceptions, and Traps

Interview Questions

What the Kernel Manages

Monolithic, Micro, and Hybrid Kernels

System Calls: The Kernel's API

Inside a System Call: The Execution Path

Boot, ELF, and the ABI

Linux, Windows, and macOS Compared

Interview Questions

Program vs Process

The Process Control Block

Process States and Transitions

fork, exec, wait, and exit

clone(): What fork and Thread Creation Share

Zombies and Orphans

Context Switching

Process Groups, Sessions, and Jobs

Interview Questions

Why CPU Scheduling Exists

Scheduling Metrics

FCFS, SJF, and SRTF

Priority Scheduling and Aging

Multilevel Queues and Feedback Queues

Multiprocessor Scheduling

Real-Time Scheduling

Linux Scheduling Classes

Fair Scheduling: From CFS to EEVDF

Interview Questions

What a Thread Is to the Kernel

Processes vs Threads

User-Level and Kernel-Level Threads

Thread Creation and Teardown

What a Thread Switch Actually Costs

Why Thread Pools Exist and How to Size Them

How Language Runtimes Map to Kernel Threads

Interview Questions

Race Conditions and Hardware Atomicity

Memory Ordering, Barriers, and False Sharing

Mutexes, Semaphores, and Condition Variables

How Blocking Works: Wait Queues and Futexes

Spinlocks, Preemption, and Interrupt Context

Deadlock: Conditions, Detection, and Prevention

Starvation, Livelock, and Priority Inversion

Interview Questions

Pipes and Named Pipes

Message Queues and Signals as IPC

Unix Domain Sockets

Network Sockets: Buffers, Backlog, and Accept Queues

Zero-Copy: sendfile, splice, and mmap

Interview Questions

The I/O Path: From write() to the Device

Device Controllers, Interrupts, and DMA

Blocking and Non-Blocking I/O

Synchronous and Asynchronous I/O

select, poll, and epoll

Readiness vs Completion, Edge vs Level

io_uring: The Completion-Based Model

Event Loops, Reactor, and Proactor

Buffering and Backpressure

Event-Driven Servers in Production

Interview Questions

The Process Address Space

Logical and Physical Memory

Contiguous Allocation and Fragmentation

How malloc Works

Kernel Memory Allocation

VSZ, RSS, PSS, and What They Mean

Memory Pressure and the OOM Killer

Interview Questions

Why Virtual Memory Exists

The MMU and Address Translation

Multilevel Page Tables

The TLB: Hits, Misses, and Invalidation

Page Replacement Algorithms

Working Sets and Thrashing

mmap and Memory-Mapped Files

Shared Libraries and Shared Pages

Huge Pages, NUMA, and ASLR

Interview Questions

The File Abstraction

File Descriptors

File Operations

Directories and Path Resolution

Hard and Symbolic Links

File Permissions

The Virtual File System Layer

File Allocation and Extents

Directory and Inode Caches

Crash Consistency

Copy-on-Write File Systems

Interview Questions

Storage Hardware

Storage Performance

Disk Scheduling Algorithms

The Block Layer

The Page Cache and Write-Back

Buffered and Direct I/O

Durability and fsync

RAID Fundamentals

Diagnosing I/O Problems

Interview Questions

Protection vs Security

Users, Groups, and Permissions

Access Control Models and Capabilities

Memory Protection

Seccomp and Syscall Filtering

Resource Limits

Common OS-Level Vulnerabilities

Interview Questions

What Virtualization Is

Virtual Machines and Hypervisors

Virtualized Memory

Containers vs Virtual Machines

Linux Namespaces

Container File Systems

PID 1 and Signal Handling

Container Resource Failures

Container Security

Interview Questions

A Systematic Debugging Method

Investigating Processes

Investigating CPU

Investigating Memory

Investigating Disk

Investigating System Calls

Investigating Network and Sockets

File Descriptor Exhaustion

Profiling and Flame Graphs

eBPF and bpftrace

Interview Questions

Operating Systems

Welcome

Course Roadmap
Join the Community

Introduction to OS

What Is an Operating System?
What Happens When You Run a Program
Setting Up Your Environment
C Survival Guide for Operating Systems
Essential System Tools
Interview Questions

Hardware Foundations

How the CPU Executes Instructions
Privilege Levels: User Mode and Kernel Mode
The Memory Hierarchy and Why Latency Matters
Interrupts, Exceptions, and Traps
Interview Questions

OS Architecture

What the Kernel Manages
Monolithic, Micro, and Hybrid Kernels
System Calls: The Kernel's API
Inside a System Call: The Execution Path
Boot, ELF, and the ABI
Linux, Windows, and macOS Compared
Interview Questions

Processes

Program vs Process
The Process Control Block
Process States and Transitions
fork, exec, wait, and exit
clone(): What fork and Thread Creation Share
Zombies and Orphans
Context Switching
Signals
Process Groups, Sessions, and Jobs
Interview Questions

CPU Scheduling

Why CPU Scheduling Exists
Scheduling Metrics
FCFS, SJF, and SRTF
Round Robin
Priority Scheduling and Aging
Multilevel Queues and Feedback Queues
Multiprocessor Scheduling
Real-Time Scheduling
Linux Scheduling Classes
Fair Scheduling: From CFS to EEVDF
Interview Questions

Threads

What a Thread Is to the Kernel
Processes vs Threads
User-Level and Kernel-Level Threads
Thread Creation and Teardown
What a Thread Switch Actually Costs
Why Thread Pools Exist and How to Size Them
How Language Runtimes Map to Kernel Threads
Interview Questions

Synchronization

Race Conditions and Hardware Atomicity
Memory Ordering, Barriers, and False Sharing
Mutexes, Semaphores, and Condition Variables
How Blocking Works: Wait Queues and Futexes
Spinlocks, Preemption, and Interrupt Context
Deadlock: Conditions, Detection, and Prevention
Starvation, Livelock, and Priority Inversion
Interview Questions

Inter-Process Communication

Pipes and Named Pipes
Shared Memory
Message Queues and Signals as IPC
Unix Domain Sockets
Network Sockets: Buffers, Backlog, and Accept Queues
Zero-Copy: sendfile, splice, and mmap
Interview Questions

I/O Systems

The I/O Path: From write() to the Device
Device Controllers, Interrupts, and DMA
Blocking and Non-Blocking I/O
Synchronous and Asynchronous I/O
select, poll, and epoll
Readiness vs Completion, Edge vs Level
io_uring: The Completion-Based Model
Event Loops, Reactor, and Proactor
Buffering and Backpressure
Event-Driven Servers in Production
Interview Questions

Memory Management

The Process Address Space
Logical and Physical Memory
Contiguous Allocation and Fragmentation
Segmentation
How malloc Works
Kernel Memory Allocation
VSZ, RSS, PSS, and What They Mean
Memory Pressure and the OOM Killer
Interview Questions

Virtual Memory

Why Virtual Memory Exists
The MMU and Address Translation
Paging
Multilevel Page Tables
The TLB: Hits, Misses, and Invalidation
Page Faults
Demand Paging
Page Replacement Algorithms
Working Sets and Thrashing
Copy-on-Write
mmap and Memory-Mapped Files
Shared Libraries and Shared Pages
Huge Pages, NUMA, and ASLR
Interview Questions

File Systems

The File Abstraction
File Descriptors
File Operations
Directories and Path Resolution
Inodes
Hard and Symbolic Links
File Permissions
The Virtual File System Layer
File Allocation and Extents
Directory and Inode Caches
Crash Consistency
Journaling
Copy-on-Write File Systems
Interview Questions

Storage

Storage Hardware
Storage Performance
Disk Scheduling Algorithms
The Block Layer
The Page Cache and Write-Back
Buffered and Direct I/O
Durability and fsync
RAID Fundamentals
Diagnosing I/O Problems
Interview Questions

Protection and Security

Protection vs Security
Users, Groups, and Permissions
Access Control Models and Capabilities
Memory Protection
Seccomp and Syscall Filtering
Resource Limits
Common OS-Level Vulnerabilities
Side Channels
Interview Questions

Virtualization and Containers

What Virtualization Is
Virtual Machines and Hypervisors
Virtualized Memory
Containers vs Virtual Machines
Linux Namespaces
Control Groups
Container File Systems
PID 1 and Signal Handling
Container Resource Failures
Container Security
Interview Questions

Observability and Debugging

A Systematic Debugging Method
Investigating Processes
Investigating CPU
Investigating Memory
Investigating Disk
Investigating System Calls
Investigating Network and Sockets
File Descriptor Exhaustion
Profiling and Flame Graphs
eBPF and bpftrace
Interview Questions

Directories and Path Resolution

Medium Priority

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File Operations Inodes