Linux File System Explained (with Practical Examples)

What is the Linux File System?

Linux organizes everything under a single root directory /. Disks, USB drives, and even virtual files are mounted into this tree. Unlike Windows drive letters (C:, D:), Linux mounts locations to paths like /mnt/data.

Quick Start: Core Navigation Commands

# where am I?
pwd

# list files with details (human-readable sizes)
ls -alh

# change directory
cd /etc

# create, move, copy, remove
touch notes.txt
mv notes.txt /tmp/
cp /etc/hosts ~/hosts.backup
rm -i ~/hosts.backup

# show a tree of directories (install tree first)
# Ubuntu/Debian:
sudo apt install -y tree
# CentOS/AlmaLinux:
sudo dnf install -y tree
tree -L 2 /

Directory Layout (FHS essentials)

Ubuntu/Debian vs CentOS/AlmaLinux: Key Differences

• Package manager: apt (Ubuntu/Debian) vs dnf (CentOS/Alma).
• Default filesystems: Ubuntu/Debian = ext4 (often), CentOS/Alma = xfs by default.
• Service manager: All use systemd, but service names/locations under /etc may differ.
• Web root: Ubuntu’s Apache defaults to /var/www/html; RHEL family similar but package names differ.

Hands-On: Common Tasks (Both Families)

Create a directory for a project

mkdir -p ~/projects/talkecoho
cd ~/projects/talkecoho
echo "Hello Linux" > hello.txt
ls -lh

Explore configuration in /etc

# show your hosts file
sudo nano /etc/hosts

# check your network interfaces (systemd-networkd or NetworkManager may manage them)
ip a

View logs in /var/log

# follow the kernel/message log (journalctl spans virtual logs)
sudo journalctl -f
# or read classic log files
sudo tail -n 100 /var/log/syslog      # Ubuntu/Debian
sudo tail -n 100 /var/log/messages    # CentOS/AlmaLinux

Mount a new disk

# find disk name
lsblk

# create filesystem and mount (example uses /dev/sdb1)
sudo mkfs.ext4 /dev/sdb1
sudo mkdir -p /mnt/data
sudo mount /dev/sdb1 /mnt/data
df -h /mnt/data

# make it persistent across reboots by adding to /etc/fstab:
# UUID=xxxx-xxxx  /mnt/data  ext4  defaults  0  2
sudo blkid /dev/sdb1
sudo nano /etc/fstab

Permissions & Ownership (Quick Primer)

# see permissions
ls -l

# change owner and group
sudo chown user:group /var/www/html -R

# change permissions (e.g., rwxr-xr-x)
sudo chmod 755 /usr/local/bin/mytool

Typical web directories use 755 for dirs and 644 for files. Never give 777 unless you really know why.

Cheat Sheet by Distro

Ubuntu/Debian

# install software
sudo apt update && sudo apt install -y nginx

# services
sudo systemctl status nginx
sudo systemctl enable --now nginx

CentOS/AlmaLinux

# install software
sudo dnf install -y nginx

# services
sudo systemctl status nginx
sudo systemctl enable --now nginx