The Philosophy
Linux is not just a Kernel; it is a way of thinking.
- Everything is a file. (Even your hard drive, your mouse, and your RAM).
- Small, single-purpose programs. (Do one thing and do it well).
- Chainability. (Output of one program becomes the input of another).
1. The File System Hierarchy (FHS) 📂
Unlike Windows (which uses C:\, D:\), Linux starts from a single root: /.
| Path | Purpose | The “Windows” Analogy |
|---|---|---|
/ | Root. The beginning of everything. | My Computer |
/bin | Binaries. Essential user commands (ls, cp). | System32 |
/boot | Bootloader. Kernel (vmlinuz) and GRUB live here. | (Hidden EFI partition) |
/dev | Devices. Hardware represented as files (/dev/sda is your SSD). | Device Manager |
/etc | Etcetera. System-wide configuration files. | Registry / AppData |
/home | User Home. Where your data lives (/home/habibullah). | C:\Users |
/lib | Libraries. Shared code required by binaries. | .dll files |
/proc | Processes. A virtual window into the Kernel’s brain. | Task Manager details |
/root | Root’s Home. The VIP room for the Admin user. | Administrator Folder |
/var | Variables. Logs, website files, database storage. | C:\ProgramData |
Hacker Tip
You can recover deleted files from a running process by exploring
/proc/<pid>/fd.
2. The Shell (Strap Yourself In) 🐚
The Shell (Bash/Zsh) is not just a command runner; it is a full programming environment.
The Streams (I/O)
Every program has 3 connections to the outside world:
- STDIN (0): Standard Input (Keyboard).
- STDOUT (1): Standard Output (Screen).
- STDERR (2): Standard Error (Screen, specifically for errors).
Redirection & Piping
The pipe | is the most powerful operator in Linux. It connects the STDOUT of the left command to the STDIN of the right command.
# Redirection
echo "Hello" > file.txt # Overwrite file
echo "World" >> file.txt # Append to file
# Piping
cat file.txt | grep "Hello" # Read file -> Search for string
ps aux | grep firefox # List processes -> Filter for browser
# The "Black Hole"
./script.sh > /dev/null 2>&1 # Silence all output (Send to void)3. Permissions (Chmod/Chown) 🔐
Linux is multi-user by design. Every file has an Owner, a Group, and a World.
The Syntax: -rwxr-xr--
-
r= Read (4) -
w= Write (2) -
x= Execute (1)
Breakdown:
-
Owner:
rwx(7) → Can Read, Write, Run. -
Group:
r-x(5) → Can Read, Run. -
World:
r--(4) → Can only Read.
Commands:
Bash
chmod +x script.sh # Make executable
chmod 777 script.sh # Give EVERYONE access (Dangerous!)
chmod 600 private.key # Only owner can read/write (Secure)
chown user:group file # Change ownership
4. Process Management ⚡
You are the god of your machine. You decide what lives and dies.
| Command | Action |
|---|---|
ps aux | List all running processes. |
top / htop | Task Manager (Real-time CPU/RAM usage). |
kill <pid> | Ask a process to stop nicely (SIGTERM). |
kill -9 <pid> | Force Kill. The Kernel assassinates the process immediately (SIGKILL). |
Ctrl + Z | Pause current process (send to background). |
bg / fg | Resume process in background or foreground. |
5. Text Manipulation (The Superpowers)
GUI editors open files. Linux tools stream files.
-
grep: Search for patterns.
Bash
grep -r "TODO" . # Find all "TODO" comments in current directory -
head / tail: View start or end.
Bash
tail -f /var/log/nginx/access.log # Watch server hits in real-time -
sed: Stream Editor (Find & Replace).
Bash
sed -i 's/foo/bar/g' config.txt # Replace 'foo' with 'bar' inside file
6. Networking from CLI 🌐
-
curl: The Swiss Army Knife of HTTP.
Bash
curl -I google.com # Check headers curl -L habibullah.dev # Follow redirects -
ss / netstat: Who is listening?
Bash
ss -tuln # Show all TCP/UDP ports listening on numbers -
ssh: Remote access.
Bash
ssh -i key.pem user@192.168.1.10
7. Package Management (DNF/RPM) 📦
Since you run Fedora, you use dnf.
Bash
sudo dnf update # Update entire system
sudo dnf install git # Install package
sudo dnf search "browser" # Find package
sudo dnf history # Undo mistakes (Rollback installs)
Linked Notes
-
Fedora-Workstation - My specific configuration.
-
Linux-Kernel-Internals - How the OS works deeper down.
-
Docker-Ultimate-Guide - Running Linux inside Linux.