Making and Mounting a File System

 

1. Why Do We Need This?

A system may have:

• Multiple disks

• Multiple partitions

• Different file system types

👉 But users should see one unified directory tree

✔ Solution:

• Create file systems

• Mount them into a single hierarchy

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2. Making a File System

📌 Tool: mkfs (make file system)

🔑 Purpose

Creates a new, empty file system on a storage device (like a disk partition)

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📖 Syntax

mkfs -t <filesystem_type> <device>

Example

mkfs -t ext3 /dev/sda1

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⚙️ What mkfs Does Internally

When you run mkfs, it:

1. Initializes the disk partition

2. Creates essential structures:

   • Root directory (/)

   • Inodes

   • Free space management

3. Writes metadata structures onto disk

👉 After this:

• The disk contains a valid file system

• But it is still not accessible to users

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3. Mounting a File System

📌 System Call: mount()

📌 Command:

mount -t <type> <device> <mount_point>

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🔑 Concept

👉 Mounting =
Attaching a file system to an existing directory

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📖 Example

mount -t ext3 /dev/sda1 /home/users

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🔄 What Happens During Mount?

• /home/users becomes the entry point (mount point)

• The root of new file system is attached there

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📂 Before Mount

/
├── home
│   └── users  (empty or existing dir)

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📂 After Mount

/
├── home
│   └── users  → root of new filesystem
                 ├── a
                 │   └── foo
                 └── b
                     └── foo

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📌 Accessing Files

Path	Meaning
/home/users/	root of new FS
/home/users/a	subdirectory
/home/users/a/foo	file

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4. Key Insight: Unified Namespace

👉 Mount creates a single global directory tree

✔ User does NOT see:

• Different disks

• Different partitions

✔ Everything appears under /

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5. Multiple File Systems in One Tree

Example output of mount:

/dev/sda1 on /     type ext3
proc on /proc      type proc
tmpfs on /dev/shm  type tmpfs

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🔍 Types of File Systems

Type	Purpose
ext3	Disk-based storage
proc	Process information
tmpfs	Temporary memory-based FS
AFS	Distributed file system

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🔑 Insight

👉 Different file systems can coexist:

• Disk storage

• Memory storage

• Network storage

✔ All appear as one system

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6. Important Concepts

📌 Mount Point

• A directory where new FS is attached

• Must exist before mounting

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📌 Root of Mounted FS

• The root (/) of new FS appears at mount point

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📌 Transparency

👉 Users don’t need to know:

• Where data is physically stored

• Which device is used

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7. Advantages

✅ Simplicity

• Single directory structure

✅ Flexibility

• Add/remove storage easily

✅ Modularity

• Different FS types supported

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8. Summary

Emphasize:

👉 Key abstraction

Multiple file systems → One unified tree

👉 Two-step process:

1. mkfs → create filesystem

2. mount → make it accessible

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