Comment partitionner un disque Linux avec fdisk

Understanding Disk Partitioning

Before a newly attached hard drive can be used on a Linux server, it typically needs to be partitioned. Partitions divide a physical disk into logical sections that can later be formatted with file systems and mounted for use by the operating system.

Linux provides several partitioning utilities, but one of the most widely available tools is fdisk. It is included with most Linux distributions and allows administrators to create, modifier, and manage partition tables directly from the command line.

Because fdisk works at a very low level, it is important to use it carefully. Incorrect changes can result in permanent data loss.

Important Warning

Avant d'apporter des modifications:

• Verify the correct disk device.
• Ensure the disk is not actively in use.
• Créer sauvegardes of any important data.
• Confirm you are not modifying your operating system disk by mistake.

Modifying the wrong partition table can make data inaccessible and may require recovery procedures.

Identifying the Target Disk

Before launching fdisk, identify the device name assigned to the new drive.

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Courir:

fdisk -l

You can also use:

lsblk

Example output:

NAME   SIZE TYPE
sda    500G disk
├─sda1 100G part
├─sda2 200G part
└─sda3 200G part

sdb    100G disk

In this example:

/dev/sdb

is a new unpartitioned disk.

Starting fdisk

Launch fdisk using the target disk:

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fdisk /dev/sdb

On a brand-new drive, you may see a message indicating that no partition table exists yet.

Exemple:

Device contains neither a valid DOS partition table nor GPT partition table.

This is normal for a new disk.

Displaying Available Commands

At any time, display available commands:

m

Common commands include:

Creating a GPT Partition Table

Modern systems commonly use GPT instead of the older MBR format.

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Create a GPT partition table:

g

Benefits of GPT include:

• Support for disks larger than 2 TB
• More partitions
• Fiabilité améliorée
• Modern UEFI compatibility

For most current deployments, GPT is recommended.

Choose the partition-table type before creating partitions. Running g after adding partitions starts a new empty table and discards the pending layout. Use it only on the verified empty target disk.

Creating a New Partition

To create a partition:

n

With GPT, select the partition number and accept the default start sector. There are no primary or extended partition types. On an older MBR/DOS disk, fdisk may instead ask for p (primary) or e (extended), and primary partition numbers are limited to 1–4.

Choosing the First Sector

fdisk will suggest the default starting sector:

First sector:

In most situations, simply press Enter to accept the default.

Exemple:

Using default value

Specifying Partition Size

You can define partition size using:

• Sectors
• Megabytes
• Gigabytes

Exemples:

+500M
+10G
+100G

To create a 10 GB partition:

+10G

fdisk then creates the partition.

Viewing the Current Partition Layout

Display the partition table:

p

Exemple:

Device      Start      End  Sectors Size Type
/dev/sdb1    2048 20973567 20971520  10G Linux

This confirms the first partition has been created successfully.

Creating Additional Partitions

To create another partition:

n

Select the next partition number:

2

Accept the default first sector and choose the desired size.

Exemple:

+50G

Repeat the process until all desired partitions are created.

Using Remaining Free Space

To create a partition that consumes all remaining disk space:

1. Create a new partition.
2. Accept the default first sector.
3. Accept the default ending sector by pressing Enter.

Exemple:

Using default value

The partition will automatically use all remaining available space.

Example Partition Layout

After creating two partitions, the output may resemble:

Device      Start       End    Sectors  Size Type
/dev/sdb1    2048  20973567   20971520   10G Linux
/dev/sdb2 20973568 209715199 188741632   90G Linux

Changing a Partition Type

Par défaut, fdisk usually assigns:

Linux

If another partition type is required:

t

You can list available partition types:

L

Les exemples incluent:

• Linux
• Linux Swap
• EFI System
• Linux LVM

Saving Changes

Once the partition layout is correct, save the configuration:

w

fdisk writes the partition table to disk and exits.

Example output:

The partition table has been altered.
Syncing disks.

Exiting Without Saving

If you made a mistake and want to cancel all pending changes:

q

This exits fdisk without modifying the disk.

Refreshing Partition Information

Sometimes Linux does not immediately reload the updated partition table.

You can force a refresh:

partprobe

Or:

partx -u /dev/sdb

In some situations, a reboot may still be required.

Creating a Filesystem

Formatting destroys existing data on the selected partition. Choose exactly one of the following formats; do not run all three commands. The later mount and fstab example assumes ext4. A swap partition uses swapon and a swap fstab entry instead of mounting on /data.

Partitioning alone does not make the partition usable.

Create a filesystem:

EXT4

mkfs.ext4 /dev/sdb1

XFS

mkfs.xfs /dev/sdb1

Linux Swap

mkswap /dev/sdb1

Mounting the Partition

Create a mount point:

mkdir -p /data

Mount the partition:

mount /dev/sdb1 /data

Vérifier:

df -h

Exemple:

/dev/sdb1   9.8G  200M  9.1G  3% /data

Configuring Automatic Mounting

To mount automatically after reboot:

Retrieve the UUID:

blkid

Exemple:

UUID="12345678-abcd-1234-abcd-123456789abc"

Add an entry to:

/etc/fstab

Exemple:

UUID=12345678-abcd-1234-abcd-123456789abc /data ext4 defaults 0 2

Test the configuration:

mount -a

Common Troubleshooting

Device Does Not Appear

The scan command below applies only to the correct SCSI host, which may not be host0. It is not a generic fix for NVMe or every virtual-disk bus. Check the provider attachment status and the actual device bus first.

Rescan storage devices:

echo "- - -" > /sys/class/scsi_host/host0/scan

Or reboot the server.

Partition Table Not Reloaded

Courir:

partprobe

If unsuccessful, reboot the server.

Incorrect Device Selected

Never save changes if you notice the wrong disk was selected.

Exit immediately:

q

before writing the partition table.

Best Practices

• Use GPT for modern systems.
• Verify disk names before modifying partitions.
• Create backups before partitioning.
• Use UUIDs in /etc/fstab.
• Leave room for future growth when planning partitions.
• Avoid modifying active production disks without maintenance planning.

Final Notes

fdisk remains one of the most reliable and widely available Linux disk partitioning tools. Whether you are preparing additional storage on a serveur dédié, creating separate partitions for applications, or configuring new data volumes, understanding how to use fdisk safely is an essential Linux administration skill.

Once partitions are created, formatted, and mounted, the new storage becomes available for applications, bases de données, sauvegardes, and general server operations.