How Linux Works Internally (Kernel, Process, Memory)
Introduction
Understanding how Linux works internally is essential for developers, system administrators, and DevOps engineers. Linux powers servers, cloud platforms, containers, and embedded systems, yet many users only interact with it through commands and tools.
This guide explains Linux internals in a simple and practical way, focusing on three core components: the Linux kernel, process management, and memory management.
High-Level Architecture of Linux
Linux follows a layered architecture:
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Hardware – CPU, RAM, disk, network
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Kernel – Core of the operating system
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System Libraries – Interfaces for applications
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User Space Applications – Shell, apps, services
The kernel acts as the bridge between hardware and user programs.
What Is the Linux Kernel?
The Linux kernel is the heart of the operating system. It directly communicates with hardware and manages system resources.
Responsibilities of the Linux Kernel
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Process scheduling
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Memory management
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Device drivers
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File system access
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Networking
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Security and permissions
Linux uses a monolithic kernel, meaning most OS services run in kernel space for high performance.
Kernel Space vs User Space
User Space
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Where applications run
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Limited access to hardware
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Safer execution environment
Kernel Space
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Executes critical OS code
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Full access to hardware
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Faster but sensitive to errors
Applications interact with the kernel using system calls.
System Calls: How Applications Talk to the Kernel
When a user runs a command like:
ls
The flow is:
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Command executes in user space
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A system call requests file access
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Kernel communicates with disk
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Results return to user space
Common system calls include read, write, fork, and exec.
Process Management in Linux
A process is a running instance of a program.
Process Lifecycle
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Created using fork()
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Program loaded using exec()
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Scheduled by the kernel
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Terminated after completion
Each process has a process ID, parent process, and execution state.
Process Scheduling
Linux uses the Completely Fair Scheduler (CFS) to allocate CPU time fairly among processes.
Key features:
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Fair CPU allocation
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Priority-based scheduling
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Fast context switching
Threads in Linux
Linux treats threads as lightweight processes.
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Threads share memory
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Faster execution than full processes
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Widely used in modern applications
Memory Management in Linux
Linux uses virtual memory to efficiently manage system RAM.
Key Memory Concepts
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Virtual memory
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Physical memory
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Swap space
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Page cache
Virtual Memory Explained
Each process is given its own virtual address space. This ensures isolation, security, and efficient memory usage.
Paging and Swapping
Paging divides memory into fixed-size pages loaded on demand. Swapping moves inactive pages to disk to free RAM.
Command to view memory usage:
free -h
File System Interaction
Linux treats everything as a file, including devices, sockets, and pipes. The Virtual File System layer allows Linux to support multiple file systems.
Device Drivers and Hardware Access
Device drivers enable the kernel to communicate with hardware components. Drivers can be loaded dynamically.
Command to view loaded modules:
lsmod
Security and Permissions Internals
Linux security is enforced using user IDs, group IDs, file permissions, and capabilities to restrict access.
Linux Boot Process (Overview)
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BIOS or UEFI initializes hardware
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Bootloader loads the kernel
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Kernel initializes devices
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systemd starts services
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Login prompt appears
Why Understanding Linux Internals Matters
Understanding Linux internals helps with debugging, performance optimization, automation, and interview preparation.
FAQs
What is the role of the Linux kernel?
The kernel manages hardware, processes, memory, and system calls.
How does Linux manage memory?
Linux uses virtual memory, paging, and swapping for efficient memory management.
Conclusion
Understanding how Linux works internally provides deep insight into system behavior. Mastering kernel, process, and memory concepts is essential for developers and DevOps professionals.