Disk Partitioning with fdisk

Disk Partitioning with fdisk

fdisk is the standard interactive tool for partitioning MBR (Master Boot Record) and GPT disks on Linux. It works in a menu-driven mode where changes are staged in memory and only written to disk when you save. Understanding fdisk well enough to safely partition a new data disk is an essential skill for Ubuntu server administration.

When to use fdisk

Use fdisk for interactive partitioning of disks up to 2 TB. Use parted for larger disks or automation. Both work fine for GPT on modern systems.

Inspecting disks and partitions

# List all block devices and their partitions
lsblk
lsblk -f    # Include file system info

# List all disks and their partition tables
sudo fdisk -l

# List a specific disk
sudo fdisk -l /dev/sdb

# Show partition table type and partitions
sudo parted /dev/sdb print

lsblk output showing disks and partitions

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   50G  0 disk
├─sda1   8:1    0   49G  0 part /
└─sda2   8:2    0    1G  0 part [SWAP]
sdb      8:16   0  500G  0 disk            ← New unpartitioned disk

Creating partitions with fdisk

⚠️ WARNING: Partitioning a disk that has data will destroy that data. Always verify you have the correct disk with lsblk and fdisk -l before running any partitioning commands. On a production server, confirm the disk is /dev/sdb (not sda which is usually the OS disk). Double-check disk size matches what you expect.

# Start fdisk on a new disk
sudo fdisk /dev/sdb

Interactive fdisk session — creating a single partition

Welcome to fdisk (util-linux 2.37.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): g       ← Create GPT partition table (use 'o' for MBR)
Created a new GPT disklabel.

Command (m for help): n       ← New partition
Partition number (1-128, default 1): 1
First sector (2048-1048575966, default 2048): [Enter]     ← Accept default start
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-1048575966, default 1048575966): [Enter]    ← Use entire disk

Created a new partition 1 of type 'Linux filesystem' and of size 500 GiB.

Command (m for help): p       ← Print partition table to verify
Device     Start        End    Sectors  Size Type
/dev/sdb1  2048  1048575966  1048573919  500G Linux filesystem

Command (m for help): w       ← Write changes to disk
The partition table has been altered.
Syncing disks.

# After creating partition: create file system and mount
sudo mkfs.ext4 /dev/sdb1
sudo mkdir -p /data
sudo mount /dev/sdb1 /data

# Add to /etc/fstab for persistent mount
UUID=$(sudo blkid -s UUID -o value /dev/sdb1)
echo "UUID=$UUID  /data  ext4  defaults,noatime  0  2" | sudo tee -a /etc/fstab
sudo mount -a    # Test

Deleting partitions

# Delete a partition in fdisk
sudo fdisk /dev/sdb
# d → delete partition
# 1 → partition number
# w → write changes

Partitioning for common scenarios

# Scenario: 500 GB data disk — one large partition for LVM (recommended for flexibility)
# In fdisk on /dev/sdb:
# g   → GPT
# n   → new partition
# 1, Enter, Enter   → one partition using all space
# t   → change type
# 30  → type "Linux LVM" (allows LVM to use it later)
# w   → write

# Scenario: Split disk into multiple partitions
# In fdisk on /dev/sdb:
# g   → GPT
# n → 1 → Enter → +100G     (first 100 GB)
# n → 2 → Enter → +200G     (next 200 GB)
# n → 3 → Enter → Enter     (rest of disk)
# w   → write

# After: make file systems and mount each
sudo mkfs.ext4 /dev/sdb1
sudo mkfs.xfs /dev/sdb2
sudo mkfs.ext4 /dev/sdb3

Conclusion

For adding a new data disk to an Ubuntu server, the standard workflow is: identify the disk with lsblk, partition with fdisk (create GPT table, single partition), format with mkfs.ext4 or mkfs.xfs, mount it, and add to /etc/fstab using its UUID. For disks that will be managed by LVM, set the partition type to "Linux LVM" in fdisk and then create the LVM physical volume with pvcreate.