Lecture 2: Linux Directories

Directory

What is a Directory?

A directory is a container for system and data files — essentially a folder used to organize files within the filesystem.

Linux vs. Windows Directory Structure

• Windows: Each drive (e.g., C:\, D:\) has its own root.
• Linux: A single root (/) exists for the entire system; all files and directories branch from it.

Linux Directory Structure

Directory	Purpose	Directory	Purpose
/bin	User Binaries.	/sbin	System Binaries.
/etc	Configuration Files.	/dev	Device Files.
/proc	Process Information.	/var	Variable Files.
/tmp	Temporary Files.	/usr	User Programs.
/home	Home Directories.	/boot	Boot Loader Files.
/lib	System Libraries.	/opt	Optional Applications.
/mnt	Mount Directory.	/media	Removable Devices.
/srv	Service Data.	/run	Volatile runtime data.

Difference Between / and /root

Directory	Description
/	The root directory, top of the Linux file hierarchy. Every directory is a subdirectory of /.
/root	The home directory of the system administrator (root user).

The /boot Directory

• Contains essential boot files, including the Linux kernel and bootloader (e.g. GRUB).
• Required for system startup; losing this directory prevents the OS from booting.
• Static and unshareable directory used before user-mode processes start.

Linux Directory Commands

Command	Description
pwd	Prints the current working directory path.
ls	Lists directory contents.
cd	Changes the current directory.
mkdir	Creates a new directory.
rmdir	Removes an empty directory.

pwd Command

Description

• pwd stands for Print Working Directory.
• Displays the absolute path of the current directory.
• Exists as both a shell built-in and a binary (/bin/pwd).

Syntax

pwd    # Print the full filename of the current working directory.
pwd -L # Use the $PWD environment variable, even if it contains symlinks
pwd -P # Resolve all symlinks

$PWD Environment Variable

• Stores the path of the current working directory.
• echo $PWD gives the same output of pwd -L.

Options

• --help: Displays help for the command.
• --version: Displays version information.

cd Command

Description

• cd stands for Change Directory.
• Used to move between directories.
• Available as a shell built-in.

Syntax

cd [directory]

Examples

cd /         # Move to the root directory
cd           # Move to home directory
cd ~         # Move to home directory
cd Documents # Move to a subdirectory
cd ..        # Move to parent directory

Absolute vs Relative Paths

• Absolute Path: Starts from / (root). Example: /home/user/Documents
• Relative Path: Starts from the current directory. Example: ../Downloads

Path Completion

• Press Tab to auto-complete filenames and directories.

ls Command

Description

Lists the files and directories within a directory (by default the current working directory).

Syntax

ls [options] [directory]

Common Options

Option	Description
-a, --all	Include hidden files (. prefix).
-A, --almost-all	Show hidden files but omit . and ...
-d, --directory	List directories themselves, not their contents.
-g	Show group ownership instead of file owner.
-h, --human-readable	Show human-readable sizes (e.g., KB, MB).
-i, --inode	Show inode numbers.
-l	Long listing format with detailed info.
-r, --reverse	Reverse the sorting order.
-R, --recursive	Recursive listing including subdirectories.
-S	Sort by file size, largest first
-t	Sort by modification time, newest first.

ls -l Format Fields

1. Permissions: e.g., -rwxr-xr-- (user/group/others).
2. Links: Number of hard links.
3. Owner: File owner.
4. Group: Group ownership.
5. Size: File size in bytes.
6. Date/Time: Last modification.
7. Name: File or directory name.

Custom Block Sizes:

Unit	Unit
K = Kilobyte	M = Megabyte
G = Gigabyte	T = Terabyte
P = Petabyte	E = Exabyte
Z = Zettabyte	Y = Yottabyte

ls -l --block-size=M  # Display sizes in megabytes

Hidden Files and Directories

• Hidden files start with a dot (.), e.g., .bashrc.
• ls -a: Lists all files including . (current directory) and .. (parent directory).
• ls -A: Lists hidden files but omits . and ...

Reasons for Hidden Files:

• Keeps directories clean.
• Hides backups or configuration files.
• Prevents accidental deletion.

Other Examples

• ls ~ -> Lists home directory contents.

• ls ../ -> Lists parent directory contents.

• ls -g -> Excludes owner column from output.

  

• ls -R -> Recursively lists subdirectories.

  

mkdir Command

Description

Creates directories in the filesystem.

Syntax

mkdir [options] directory_name

Options

Option	Description
-p / --parents	Create parent directories if needed.
-v / --verbose	Print a message for each directory created.
-m MODE	Set permissions (same format as chmod).
--help	Display help information.
--version	Show version info.

Examples

mkdir new_folder
mkdir -p dir1/dir2/dir3
mkdir -m 755 secure_dir # Create a new directory with rwx-rw-rw- permissions

rmdir Command

Description

Removes empty directories only.

Syntax

rmdir [options] directory_name

Example

rmdir temp_folder

Recursive Deletion

rmdir -p parent/child

Deletes a directory and its empty parent directories.

Renaming Directories

Linux uses the mv command to move or rename directories (and files).

There is no dedicated rename command.

Syntax

mv [options] old_name new_name

Options

Option	Description
--backup	Creates a backup before overwriting.
-f	Forces overwrite without confirmation.
-i	Asks before overwriting.
-v	Verbose output showing operations.

rename Command

Description

Used for batch renaming of multiple files or directories.
May need to be installed depending on the distribution.

Example

Installation

# Arch Linux (btw)
sudo pacman -S rename

# Debian / Ubuntu
sudo apt install rename

# Fedora
sudo yum install prename