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Understanding the Linux Operating System: A Deep Dive
1. Kernel Initialization
The kernel is the heart of the Linux operating system. During boot, several critical steps occur:
BIOS/UEFI and Bootloader:
The BIOS or UEFI firmware initializes hardware components.
The bootloader (e.g., GRUB) loads the Linux kernel (vmlinuz).
Kernel Initialization:
The kernel initializes hardware devices (CPU, memory, storage, etc.).
It sets up essential data structures (e.g., process tables, page tables).
The root filesystem is identified and mounted.
2. Init Process
The kernel starts the init process (traditionally init, but modern systems use systemd).
Init is responsible for:
Starting system services and daemons.
Managing user sessions and spawning user-space processes.
3. User Space Initialization
Init spawns the first user-space process (usually init or systemd).
User sessions (e.g., graphical desktop environments) start from here.
4. Filesystem Hierarchy
Linux follows a standard directory structure:
/: Root directory.
/bin, /sbin: Essential system binaries.
/etc: Configuration files.
/home: User home directories.
/var: Variable data (logs, caches).
/tmp: Temporary files.
/usr: User programs and libraries.
/opt: Optional software.
/dev: Device files.
/proc: Virtual filesystem for process information.
5. Processes and Scheduling
The scheduler (e.g., Completely Fair Scheduler) manages process execution.
Processes are created using fork() and exec() system calls.
Priorities, nice values, and CPU affinity affect scheduling.
6. Memory Management
Virtual memory management:
Page tables map virtual addresses to physical memory.
TLB (Translation Lookaside Buffer) caches page table entries.
Demand paging and swapping optimize memory usage.
Memory allocation:
malloc(), free() manage dynamic memory.
Kernel memory management handles system memory.
7. File I/O and System Calls
File descriptors (stdin, stdout, stderr) facilitate I/O.
System calls (e.g., open(), read(), write(), close()) interact with files.
8. Networking
Network stack:
IP, TCP, UDP protocols.
Socket API for network communication.
Network configuration:
ifconfig, ip commands.
Routing tables determine packet forwarding.
9. Security and Permissions
Users, groups, and permissions control access.
sudo allows privilege escalation.
File integrity checks (e.g., md5sum, sha256sum) verify file integrity.
10. Device Drivers
Kernel modules manage hardware devices.
Examples: usb-storage, e1000 (Ethernet), i915 (graphics).
11. Logging and Debugging
syslog and dmesg provide system logs.
Debugging tools (e.g., strace, gdb) help diagnose issues.
12. Shutdown and Reboot
Init sends signals to processes.
Filesystems are unmounted.
The system halts or reboots.
🌟 Cheatsheet Linux🐧
Linux Basics:
Commands:
ls: List files and directories.
cd: Change directory.
pwd: Print working directory.
cp: Copy files or directories.
mv: Move or rename files.
rm: Remove files or directories.
File Permissions:
chmod: Modify file permissions.
chown: Change file ownership.
chgrp: Change group ownership.
Processes:
ps: List running processes.
top: Monitor system processes.
kill: Terminate processes.
nice: Adjust process priority.
Package Management:
yum (RPM-based systems): Install, update, and manage packages.
apt-get (Debian-based systems): Similar functionality.
File System Hierarchy:
Understand the directory structure:
/: Root directory.
/bin: Essential system binaries.
/etc: Configuration files.
/home: User home directories.
/var: Variable data (logs, caches).
/tmp: Temporary files.
/usr: User programs and libraries.
/opt: Optional software.
/dev: Device files.
/proc: Virtual filesystem for process information.
Networking:
ifconfig or ip: Network configuration.
ping: Check network connectivity.
netstat: Network statistics.
ssh: Secure shell for remote access.
iptables: Firewall rules.
Shell Scripting:
Create and execute shell scripts:
Variables.
Loops (for, while).
Conditionals (if, else).
Functions.
Input/output redirection.
System Administration:
User management:
useradd, userdel, passwd.
Disk management:
df, du, mount.
Cron jobs:
crontab.
Security:
sudo: Execute commands with superuser privileges.
File integrity checks:
md5sum, sha256sum.
Firewalls and SELinux.
Sharing working overview, and there’s much more to explore!
Feel free to ask questions and share with beginners starting with AWS DevOps. Happy learning! 🌟🐧
