fdisk Command Linux: Complete Guide to Disk Partition Management

The fdisk command is one of the most powerful and essential tools for disk partition management in Linux systems. Whether you’re setting up a new system, adding storage, or managing existing partitions, understanding fdisk is crucial for any Linux administrator or power user.

What is fdisk Command?

The fdisk (format disk) command is a command-line utility that allows you to create, delete, modify, and display disk partitions on Linux systems. It works with MBR (Master Boot Record) and GPT (GUID Partition Table) partition schemes, making it versatile for both legacy and modern systems.

Key Features of fdisk:

• Create and delete partitions
• Change partition types
• Display partition information
• Set bootable flags
• Support for various file systems
• Interactive and non-interactive modes

Basic fdisk Syntax

The basic syntax of the fdisk command is:

fdisk [options] device

Where device is typically a disk like /dev/sda, /dev/sdb, etc.

Common Options:

• -l – List partition tables
• -s – Display partition size
• -u – Change display units
• -c – Disable DOS compatibility mode
• -h – Display help information

Viewing Disk Information

List All Available Disks

To see all available disks and their partitions:

sudo fdisk -l

Sample Output:

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c7b8c

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
/dev/sda2              64       60802   487875584   8e  Linux LVM

View Specific Disk Information

To examine a specific disk:

sudo fdisk -l /dev/sda

Check Partition Size

To display the size of a specific partition:

sudo fdisk -s /dev/sda1

Output:

512000

Interactive fdisk Mode

The interactive mode is where fdisk’s real power lies. To enter interactive mode:

sudo fdisk /dev/sda

Welcome Message:

Welcome to fdisk (util-linux 2.31.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help):

Essential Interactive Commands

Creating Partitions with fdisk

Step-by-Step Partition Creation

Let’s create a new partition on /dev/sdb:

sudo fdisk /dev/sdb

Step 1: Check current partition table

Command (m for help): p

Disk /dev/sdb: 10 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System

Step 2: Create new partition

Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-20971519, default 2048): 
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-20971519, default 20971519): +5G

Step 3: Verify the new partition

Command (m for help): p

Disk /dev/sdb: 10 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048    10487807     5242880   83  Linux

Step 4: Write changes

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

Partition Types and File Systems

Common Partition Type IDs

Changing Partition Type

To change a partition type from Linux to Linux swap:

Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): 82
Changed type of partition 'Linux' to 'Linux swap / Solaris'

Advanced fdisk Operations

Creating Extended and Logical Partitions

For more than 4 partitions on MBR systems, you need extended partitions:

# Create extended partition
Command (m for help): n
Partition type:
   p   primary (3 primary, 0 extended, 1 free)
   e   extended
Select (default e): e
Selected partition 4

# Create logical partition within extended
Command (m for help): n
All primary partitions are in use
Adding logical partition 5

Setting Bootable Flag

To make a partition bootable:

Command (m for help): a
Partition number (1-4): 1
Command (m for help): p

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux

Practical Examples and Use Cases

Example 1: Setting Up a Dual-Boot System

Creating partitions for a Windows/Linux dual-boot setup:

# Partition 1: Windows (100GB)
n → p → 1 → default → +100G → t → 1 → 07

# Partition 2: Linux Root (50GB)
n → p → 2 → default → +50G → t → 2 → 83

# Partition 3: Linux Swap (8GB)
n → p → 3 → default → +8G → t → 3 → 82

# Partition 4: Shared Data (remaining space)
n → p → 4 → default → default → t → 4 → 07

Example 2: Creating LVM Setup

Preparing partitions for LVM (Logical Volume Manager):

# Create LVM partition
Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-41943039, default 2048): 
Last sector (2048-41943039, default 41943039): 

# Change to LVM type
Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): 8e
Changed type of partition 'Linux' to 'Linux LVM'

Safety and Best Practices

Important Safety Guidelines

• Always backup data before partitioning
• Use ‘q’ to quit without saving if you make mistakes
• Double-check device names to avoid wrong disk operations
• Test in virtual machines first when learning
• Understand the difference between MBR and GPT

Pre-partitioning Checklist

# 1. Identify the correct disk
lsblk
df -h

# 2. Unmount any mounted partitions
sudo umount /dev/sdb1

# 3. Check for any processes using the disk
sudo lsof /dev/sdb*

# 4. Create backup if necessary
sudo dd if=/dev/sdb of=/backup/sdb_backup.img

Troubleshooting Common Issues

Partition Table Corruption

If you encounter partition table errors:

# Create backup of partition table
sudo sfdisk -d /dev/sda > partition_backup.txt

# Restore from backup
sudo sfdisk /dev/sda < partition_backup.txt

Device Busy Error

When fdisk shows “Device is busy”:

# Check mounted filesystems
mount | grep /dev/sda

# Check for swap usage
sudo swapoff -a

# Kill processes using the device
sudo fuser -km /dev/sda1

Partition Not Recognized

Force kernel to re-read partition table:

# For specific device
sudo partprobe /dev/sda

# For all devices
sudo partprobe

Alternative Tools and Modern Approaches

When to Use fdisk vs Other Tools

• fdisk: Traditional MBR partitioning, scripting, basic operations
• gdisk: GPT partitioning, modern systems
• parted: Both MBR and GPT, resize operations
• cfdisk: User-friendly curses interface

Scripting with fdisk

For automated partitioning:

#!/bin/bash
# Automated partitioning script
{
echo n # New partition
echo p # Primary
echo 1 # Partition number
echo   # Default first sector
echo +10G # Size
echo w # Write changes
} | sudo fdisk /dev/sdb

Conclusion

The fdisk command remains an essential tool for Linux system administrators and users who need to manage disk partitions. While newer tools like gdisk and parted offer additional features, fdisk’s simplicity and universal availability make it invaluable for both learning and production environments.

Remember to always exercise caution when working with disk partitions, as incorrect operations can lead to data loss. Practice these commands in safe environments, maintain regular backups, and gradually build your confidence with this powerful partitioning tool.

Whether you’re setting up a new system, expanding storage, or troubleshooting partition issues, mastering fdisk will significantly enhance your Linux administration skills and provide you with the foundation for more advanced storage management techniques.