On Windows, you have drive letters (C:\, D:\). On Linux, there is only one starting point: /, called the root directory. Everything — disks, USB drives, processes, network sockets — is represented as a file or directory somewhere under /.
Why a Single Hierarchy?
This design, inherited from Unix, makes the system consistent and scriptable. You never need to know which physical disk something is on — you just know its path. External drives are "mounted" into the tree, meaning they appear as directories like /mnt/data or /media/usb.
The Most Important Directories
/ — Root
The top of the entire filesystem. No directory is above /. Only the root user can write here directly.
/etc — Configuration Files
System-wide configuration lives here. Nearly every service you install puts its config in /etc:
/etc/nginx/nginx.conf— Nginx web server config/etc/ssh/sshd_config— SSH server settings/etc/fstab— Disk mount configuration/etc/hosts— Local hostname-to-IP mappings
/home — User Home Directories
Each regular user gets a directory here: /home/alice, /home/bob. This is where personal files, shell configs (.bashrc, .bash_history), and application data live. The root user's home is /root, not under /home.
/var — Variable Data
Data that changes over time: logs, databases, caches, mail spools.
/var/log— System and application log files/var/lib— Application state (e.g., database files)/var/tmp— Temporary files that persist across reboots
/tmp — Temporary Files
Temporary scratch space, cleared on reboot. Programs use this for short-lived files. Anyone can write here.
/bin and /sbin — Essential Binaries
/bin contains commands needed to boot and repair the system: ls, cp, mv, bash. /sbin contains system administration binaries: fdisk, fsck, iptables. On modern systems (Ubuntu 20.04+, RHEL 8+) these are symlinked to /usr/bin and /usr/sbin.
/usr — User Programs
The bulk of installed software lives here:
/usr/bin— User commands installed by packages/usr/lib— Shared libraries/usr/share— Architecture-independent data (docs, icons)/usr/local— Software compiled and installed manually (not by the package manager)
/proc and /sys — Virtual Filesystems
These directories contain no real files. They're interfaces to the running kernel:
/proc/cpuinfo— CPU details/proc/meminfo— Memory usage/proc/1/— Information about the process with PID 1 (systemd)/sys/class/net/— Network interface settings
/dev — Device Files
Hardware devices appear as files: /dev/sda (first disk), /dev/null (discard everything written to it), /dev/zero (produces endless zero bytes), /dev/random (random data source).
/opt — Optional Software
Third-party applications that don't follow the standard layout install here. Example: /opt/google/chrome/.
Navigating the Hierarchy
Two types of paths:
- Absolute path: starts with
/, e.g./etc/nginx/nginx.conf. Always unambiguous. - Relative path: relative to your current directory, e.g.
../config/settings.json.
Special symbols:
~— Your home directory (/home/yourname).— Current directory..— Parent directory
Quick reference commands:
pwd # print working directory (where am I?)
ls /etc # list contents of /etc
ls -la ~ # list home directory with hidden files
cd /var/log # change to /var/log
cd ~ # return home
cd .. # go up one levelIn the next lesson, you'll go deeper into the terminal itself — how to use it effectively with shortcuts, history, and command composition.