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Linux lets you divide a physical disk into multiple partitions, each with its own filesystem. For example, on a 2 TB SSD you might allocate 1 TB for Windows (NTFS) and 1 TB for Linux (ext4). Partitioning keeps filesystems separate and lets each OS manage its space independently.

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Why Partition a Disk?

  • Separate operating systems (e.g., Windows vs. Linux)
  • Isolate data, swap, and boot partitions
  • Use different partition table formats: MBR (DOS) vs. GPT (modern systems)
Leaving 1 MiB unallocated at the start of the disk is a best practice. Many bootloaders require this alignment for optimal performance.

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1. Viewing Existing Partitions

Use lsblk to list block devices and their partitions: 
lsblk
Only entries with TYPE part are actual partitions: 
$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda       8:0    0   20G  0 disk
├─sda1    8:1    0    1G  0 part /boot
├─sda2    8:2    0   19G  0 part
│ ├─cs-root 253:0  0   17G  0 lvm  /
│ └─cs-swap 253:1  0    2G  0 lvm  [SWAP]
sdb       8:16   0   10G  0 disk
sr0      11:0    1 1024M  0 rom
ColumnMeaning
NAMEDevice name (sda, sdb, etc.)
SIZEDisk or partition size
TYPEdisk, part, or lvm
MOUNTPOINTWhere it’s mounted (if applicable)

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2. Inspecting the Partition Table with fdisk

To view the partition table on /dev/sda, run: 
sudo fdisk --list /dev/sda
Sample output: 
Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xb65442dd

Device         Boot    Start      End  Sectors Size Id Type
/dev/sda1      *        2048   2099199  2097152   1G 83 Linux
/dev/sda2      2099200 41943039 39843840  19G  8e Linux LVM
  • Disklabel type: dos indicates an MBR partition table.
  • Start and End are measured in 512-byte sectors.

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3. Creating and Modifying Partitions with cfdisk

cfdisk offers an ncurses interface for partitioning. It’s especially helpful on servers without a GUI.

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Steps to Partition /dev/sdb

  1. Attach the disk (e.g., sdb) and launch: 
    sudo cfdisk /dev/sdb
  2. Select a label:
    • GPT for modern UEFI systems.
    • DOS for legacy MBR.
  3. Create partitions:
    • Navigate to Free Space → New → enter 8G → Enter.
    • Repeat in remaining free space with 2G.
  4. Resize or split (optional):
    • Highlight a partition → Resize → enter new size (e.g., 4G).
    • Use freed space to create another partition.
The image shows a terminal window displaying disk partition information for /dev/sdb, including details about partitions, free space, and options for managing them.
Disk: /dev/sdb
Size: 10 GiB, 10737418240 bytes, 20971520 sectors
Label: gpt, identifier: 42F7FA1E-9398-1741-89AA-477083B71FC3

Device       Start       End    Sectors  Size Type
/dev/sdb1    2048     8390655   8388608   4G Linux filesystem
/dev/sdb2  8390656    16779263   8388608   4G Linux filesystem
/dev/sdb3 16779264    20971486   4192223   2G Linux filesystem

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3.1 Setting a Partition Type

The default type is “Linux filesystem.” To mark /dev/sdb3 as swap:
  • Highlight sdb3 → Type → select Linux swap → Enter.
The image shows a terminal window with a menu for selecting a partition type, highlighting "Linux swap" among various options like EFI System and Microsoft reserved.
You can also choose types like EFI System for UEFI boot partitions or Microsoft reserved for Windows.
The image shows a terminal window displaying a disk partitioning tool on a CentOS system, listing partitions on the disk /dev/sdb with details like size and type.
When you Write changes in cfdisk, all partition modifications become permanent. Double-check before confirming.

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3.2 Writing and Quitting

  1. Select Write, type yes, and press Enter.
  2. Select Quit to exit cfdisk.

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4. Verifying the New Partitions

Back in the shell, confirm with lsblk: 
lsblk

NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda       8:0    0   20G  0 disk 
├─sda1    8:1    0    1G  0 part /boot
├─sda2    8:2    0   19G  0 part 
│ ├─cs-root 253:0  0   17G  0 lvm  /
│ └─cs-swap 253:1  0    2G  0 lvm  [SWAP]
sdb       8:16   0   10G  0 disk 
├─sdb1    8:17   0    4G  0 part 
├─sdb2    8:18   0    4G  0 part 
└─sdb3    8:19   0    2G  0 part 
sr0      11:0    1 1024M  0 rom
Now /dev/sdb has three partitions: two 4 GiB data partitions and one 2 GiB swap.

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Summary of Common Commands

CommandPurposeExample
lsblkList block devices and partitionslsblk
sudo fdisk —list /dev/sdXShow partition tablesudo fdisk -l /dev/sda
sudo cfdisk /dev/sdXInteractive disk partitioningsudo cfdisk /dev/sdb

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