Understanding the Linux File System

Linux organizes files in a hierarchical directory structure, often referred to as the Filesystem Hierarchy Standard (FHS). This structure starts from the root directory, represented by a forward slash /.

Directory Structure

Root Directory (/)

The root directory is the top-level directory in the Linux filesystem hierarchy. All other files and directories are descendants of this directory.

Key System Directories

Directory	Purpose
/bin	Essential command binaries (programs) that need to be available for all users
/boot	Boot loader files, kernel images, and initial ramdisk files
/dev	Device files that represent hardware devices
/etc	System-wide configuration files
/home	User home directories
/lib	Essential shared libraries and kernel modules
/media	Mount points for removable media (USB drives, CDs, etc.)
/mnt	Mount point for temporarily mounted filesystems
/opt	Optional application software packages
/proc	Virtual filesystem that provides process and kernel information
/root	Home directory for the root user
/sbin	Essential system binaries used for system administration
/srv	Data for services provided by the system
/sys	Virtual filesystem for kernel and device information (similar to /proc)
/tmp	Temporary files that are typically cleared on reboot
/usr	Secondary hierarchy for user data and applications
/var	Variable data files (logs, spool files, temporary files, etc.)

Understanding Paths

Absolute vs. Relative Paths

• Absolute path: Starts from the root directory (/), e.g., /home/user/documents/file.txt
• Relative path: Relative to the current directory, e.g., documents/file.txt

Path Shortcuts

• . (dot): References the current directory
• .. (double dot): References the parent directory
• ~ (tilde): References the home directory of the current user

File Types in Linux

Linux treats everything as a file, but there are different types:

1. Regular files: Normal files containing data, text, or programs
2. Directories: Special files that contain listings of other files
3. Links:
   • Hard links: Additional references to the same inode (data)
   • Symbolic links: Pointers to other files or directories
4. Device files:
   • Block devices: Storage devices that can be accessed in blocks (e.g., hard drives)
   • Character devices: Devices that handle data as character streams (e.g., terminals)
5. Sockets: Enable inter-process communication
6. Named pipes: Allow processes to communicate with each other

Viewing File Information

Using ls -l

When you run ls -l, you'll see output like:

-rwxr-xr-x 1 user group 5096 Jun 10 14:30 example.sh

This format provides:

• File permissions (-rwxr-xr-x)
• Number of links (1)
• Owner name (user)
• Group name (group)
• File size (5096 bytes)
• Last modification time (Jun 10 14:30)
• File name (example.sh)

Finding File Information

# Get detailed file information
stat filename

# Find files by name
find /path/to/search -name "filename"

# Find files by type
find /path/to/search -type f  # f for regular files
find /path/to/search -type d  # d for directories

# Find files by size
find /path/to/search -size +10M  # Files larger than 10MB

Disk Usage and Management

Checking Disk Space

# Show disk usage for all mounted filesystems
df -h

# Show disk usage for a specific directory
du -sh /path/to/directory

# Show disk usage for all subdirectories in current directory
du -sh */

Mounting and Unmounting Filesystems

# Mount a filesystem
sudo mount /dev/sdb1 /mnt/usb

# Unmount a filesystem
sudo umount /mnt/usb

# List all mounted filesystems
mount

File System Types

Linux supports various filesystem types:

1. ext4: The default filesystem for many Linux distributions
2. XFS: High-performance filesystem, good for large files
3. Btrfs: Modern filesystem with advanced features like snapshots
4. NTFS/FAT32: Windows compatibility filesystems
5. NFS: Network File System for remote file access

Practice Exercises

1. Navigate through the filesystem and identify the purpose of different directories
2. Create a directory structure for a project with multiple subdirectories
3. Use relative and absolute paths to navigate between directories
4. Find all files larger than 100MB in your home directory
5. Check which filesystem is using the most disk space on your system

In the next section, we'll explore Linux permissions and how to manage them.