Skip to content

kernel.md

Latest commit

 

History

History
116 lines (87 loc) · 3.73 KB

kernel.md

File metadata and controls

116 lines (87 loc) · 3.73 KB
Raw

Kernel

See the kernel version:

uname -r

Which modules are loaded:

lsmod | less

Get kernel messages:

dmesg

What the Kernel Is

The kernel is the first program that loads at boot and never stops running.
It is the only software that directly talks to hardware.

Hardware          →  Physical components (CPU, RAM, Disk, NIC)
Kernel            →  Controls hardware directly, always running
OS (full system)  →  Kernel + userland tools + utilities + GUI
Applications      →  Run in user space, request kernel services via syscalls

4 Core Responsibilities

Responsibility What It Does
Process Management Creates, schedules, kills processes; handles multitasking across CPU cores
Memory Management Allocates/frees RAM, enforces isolation, manages virtual memory
Device Management Talks to hardware via device drivers (disk, NIC, keyboard, GPU)
System Calls Only gateway for apps to request kernel services (read, write, fork, socket)

OS vs Kernel

┌──────────────────────────────────────────┐
│              USER SPACE                  │
│  Browser   IDE   Terminal   Docker CLI   │  ←  Applications
│  Package Manager   Shell   File Manager  │  ←  OS Utilities
│  GUI (GNOME/KDE)   System Libraries      │  ←  OS Layer
├──────────────────────────────────────────┤
│              KERNEL SPACE                │
│  Process Mgmt   Memory Mgmt   Scheduler  │
│  Device Drivers   Filesystem   Network   │  ←  THE KERNEL
└──────────────────────────────────────────┘
           ↕  direct hardware access
┌──────────────────────────────────────────┐
│   CPU    RAM    Disk    NIC    GPU       │  ←  Hardware
└──────────────────────────────────────────┘
Kernel Operating System
What it is Core engine Kernel + tools + utilities
Hardware access Direct Always goes through kernel
Examples Linux kernel, Windows NT Ubuntu, Windows 11, macOS, Android
Runs in Kernel space (privileged) User space (restricted)

Linux ≠ Ubuntu

Linux    =  just the kernel  (Linus Torvalds, 1991)
Ubuntu   =  Linux kernel + apt + bash + GNOME + tools
Debian   =  Linux kernel + different tools/config
Android  =  Linux kernel + Google userspace + apps

Kernel Space vs User Space

User Space    →  your app runs here  —  RESTRICTED  —  cannot touch hardware
                          ↓  system call  (the only bridge)
Kernel Space  →  kernel runs here  —  PRIVILEGED  —  full hardware access

Example — Java reading a file

Files.readString(Path.of("config.yaml"))

What actually happens:

Java IO  →  glibc  →  open() syscall  →  Linux kernel  →  disk driver  →  disk

Your code never touches the disk — the kernel does it on your behalf.

How This Relates to Docker

VM:      App → [Guest Kernel] → [Hypervisor] → [Host Kernel] → Hardware
Docker:  App → [Host Kernel] → Hardware
  • VM boots a full guest kernel → slow startup, heavy RAM usage
  • Docker container has no kernel — shares host kernel directly
  • Container lives in user space, isolated via namespaces
  • No kernel to boot → container starts in milliseconds