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Navigation and File Systems

Chapter 3: Navigation and File Systems

In Unix-like systems, "everything is a file." Whether it's your hard drive, your keyboard, or a simple text document, the shell interacts with them all through the file system hierarchy. Mastering navigation is about understanding the Filesystem Hierarchy Standard (FHS) and how to control access through permissions.

I. The Unix Directory Structure

Unlike Windows, where every drive has its own root (like C:\ or D:\), Unix systems have a single unified root (/). All storage devices are "mounted" as folders within this tree.

//bin/etc/home/varExecutablesConfig FilesUser DataVariable Logs

Key Directories to Know:

  • /bin & /usr/bin: Essential command binaries (like ls, cp).
  • /etc: System-wide configuration files (e.g., password files, network config).
  • /home: Personal directories for regular users.
  • /root: The home directory for the superuser (Administrator).
  • /tmp: Temporary files (often cleared on reboot).
  • /dev: Hardware devices represented as files (e.g., /dev/sda for a disk).

II. File Permissions (rwx)

Unix security is based on three types of access for three types of people.

PermissionFor a FileFor a Directory
Read (r)View the contents.List the files inside.
Write (w)Modify the contents.Add or delete files inside.
Execute (x)Run as a program.Enter the directory (cd).

The ls -l Breakdown

When you run ls -l, you see a string like -rwxr-xr--.

  1. -: File type (- for file, d for directory).
  2. rwx: Owner permissions.
  3. r-x: Group permissions.
  4. r--: Others (everyone else).

III. Modifying Permissions and Ownership

chmod (Change Mode)

You can use symbolic or numeric notation to change permissions.

  • Symbolic: chmod u+x script.sh (Add execute for user).
  • Numeric: chmod 755 script.sh (Owner: rwx, Group: r-x, Others: r-x).
    • Read = 4, Write = 2, Execute = 1. (4+2+1=7).

chown (Change Owner)

Requires administrative privileges (sudo).

sudo chown jane:developers report.txt
# Changes owner to 'jane' and group to 'developers'

IV. Finding Files

As the filesystem grows, you need powerful tools to find data.

find (The Powerhouse)

Searches the directory tree based on attributes.

find /home -name "*.pdf" -size +10M
# Finds all PDFs larger than 10MB in /home

locate (The Speedster)

Uses a pre-built database for near-instant results.

locate config.yaml

V. Disk Usage Analysis

  • du (Disk Usage): How much space is this folder taking?
    • du -sh . (Show summary of current folder in human-readable format).
  • df (Disk Free): How much space is left on my hard drives?
    • df -h.

In the next chapter, we'll learn how to customize our environment using Variables and Dotfiles.

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