fdisk

The fdisk command is a powerful, albeit somewhat complex, tool in Linux for partitioning hard disks. It allows you to create, delete, resize, and manage partitions on your storage devices. While graphical tools exist, understanding fdisk is important for system administrators and advanced users. This guide will walk you through its essential functionalities with detailed examples.

Understanding Partitions:

Before diving into fdisk, it’s important to grasp the concept of partitions. A partition is a logical division of a physical hard drive, allowing you to organize your storage space into separate sections. Each partition can be formatted with a different filesystem (e.g., ext4, NTFS, FAT32) and have its own independent file system.

Using fdisk:

The basic syntax of fdisk is:

sudo fdisk /dev/sdX

Replace /dev/sdX with the actual device name of your hard drive. For example, /dev/sda usually refers to the first hard drive. Always double-check the device name before proceeding, as incorrect usage can lead to data loss. The sudo command is necessary because partitioning requires root privileges.

Key fdisk Commands:

Once you’ve executed the command, you’ll be presented with the fdisk prompt. Here are some of the most important commands:

• p (print): Displays the current partition table. This is essential to see the existing partitions before making any changes.

fdisk /dev/sda
p

• n (new): Creates a new partition. You’ll be prompted to choose a partition type (primary or logical), partition number, and starting and ending cylinders.

n
p       # Primary partition (choose p or l for logical)
1       # Partition number (usually starts from 1)
<Enter> # Accept default starting sector
<Enter> # Accept default ending sector (or specify a size)

• d (delete): Deletes a partition. You’ll be prompted to specify the partition number to delete.

d
1       # Delete partition 1

• w (write): Writes the changes to the partition table. Your changes will not be saved until you execute this command.

w

• q (quit): Quits the fdisk utility without saving changes.

q

• t (type): Changes the partition type (e.g., to specify a filesystem). You’ll need the hexadecimal code for the desired type. For example, 83 is typically for Linux partitions.

t
1       # Select partition 1
83      # Linux filesystem type

Example: Creating a New Partition:

Let’s say we want to create a new primary partition on /dev/sda for a Linux system. The steps would be:

1. Open fdisk: sudo fdisk /dev/sda
2. Print the partition table: p
3. Create a new partition: n (Choose primary partition ‘p’, then choose a partition number, and accept default start/end sectors or specify a custom size.)
4. Set the partition type to Linux: t (Select the newly created partition number and then enter 83)
5. Write the changes: w
6. Exit fdisk: The system will prompt you to reload the partition table, generally by running partprobe /dev/sda

Important Considerations:

• Data Loss: Incorrect use of fdisk can lead to irretrievable data loss. Always double-check your commands and device names before executing them. It is strongly recommended to back up your data before making any partitioning changes.
• Backup: Before starting, back up your data.
• Device Names: Be extremely careful when specifying the device name. A simple typo can have disastrous consequences.

This guide provides a basic introduction to fdisk. There are more advanced options and features available, which you can look at further in the fdisk man page (man fdisk). Remember that practicing with a virtual machine is highly recommended before applying these commands to a production system.