How to Create Partition.md

How to Create a Partition

Warning: These steps modify disk partitions and can destroy data. Double-check the device name and back up any important data before proceeding.

Prerequisites

• Root access (use sudo -i or sudo su).
• A spare disk or removable media (SD card, USB drive, eMMC) with free space.
• Know the correct device name (e.g. /dev/sda, /dev/mmcblk0, /dev/nvme0n1).

Overview

This document explains how to create a new partition using fdisk, force the kernel to re-read the partition table, and optionally create a filesystem and mount the partition.

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Steps

1. List disks and existing partitions

Identify the correct disk before making changes:

# list block devices and partitions
lsblk
# or show detailed partition/size information
sudo fdisk -l
# inspect a specific device (example)
lsblk /dev/sda
# or for SD/eMMC devices
lsblk /dev/mmcblk0

Carefully confirm which device (for example /dev/sda or /dev/mmcblk0) you will modify.

2. Start fdisk on the target disk

Open an interactive fdisk session for the target disk (replace /dev/sdX with your device):

sudo fdisk /dev/sdX

3. Create a new partition

Inside the fdisk prompt:

• Type n and press Enter to create a new partition.
• Choose partition type:
  • p — primary
  • e — extended (usually not needed on modern systems)
• Choose a partition number (or press Enter to accept the default).
• For the first sector press Enter to accept the default (recommended).
• For the last sector you can press Enter to use the remaining space, or specify a size like +1G, +500M, etc.

Example interactive session:

Command (m for help): n
Select (default p): p
Partition number (1-4, default 1): [Enter]
First sector (2048-..., default 2048): [Enter]
Last sector, +sectors or +size{K,M,G,T,P} (2048-..., default ...): +2G

4. (Optional) Change partition type/code

The default type is Linux (code 83). To change it:

• Type t and Enter.
• Enter the partition number if prompted.
• Enter the hex code for the type, or type L to list available codes and choose one.

Common type codes:

• 83 — Linux filesystem
• 82 — Linux swap
• 07 — NTFS/exFAT
• ef — EFI System (FAT)

5. Write the partition table and exit

When ready, save changes with:

Command (m for help): w

This writes the partition table to disk and exits fdisk. If you quit without w (for example with q), no changes will be saved.

6. Make the kernel re-read the partition table

Force the kernel to re-read the partition table so the new partition becomes visible:

sudo partprobe /dev/sdX
# or
sudo partx -a /dev/sdX
# verify
lsblk
sudo fdisk -l /dev/sdX

If the kernel cannot re-read the table, a reboot may be required.

7. (Optional) Create a filesystem and mount the partition

After creating a partition (for example /dev/sdX1) you can create a filesystem:

# create ext4 filesystem
sudo mkfs.ext4 /dev/sdX1
# or create FAT32 (useful for SD cards / cross-platform):
sudo mkfs.vfat -F 32 /dev/sdX1

Mount it:

sudo mkdir -p /mnt/my-partition
sudo mount /dev/sdX1 /mnt/my-partition
# check usage
df -h /mnt/my-partition

To auto-mount at boot, use the partition UUID in /etc/fstab:

sudo blkid /dev/sdX1
# example fstab entry (replace UUID and mount point):
# UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx  /mnt/my-partition  ext4  defaults  0  2

Tips and precautions

• ALWAYS double-check the device name; writing to the wrong device will destroy data.
• On eMMC/SD devices, partitions are named like /dev/mmcblk0p1 (note the p before the number).
• On NVMe devices, device names are like /dev/nvme0n1 and partitions like /dev/nvme0n1p1.
• Use lsblk and fdisk -l to confirm sizes and partitions before and after changes.

References

• fdisk manual: man fdisk
• lsblk manual: man lsblk

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