eolas/zk/Linux_disk_partitions.md

---
tags:
  - disks
  - Linux
  - procedural
---

# Linux disk partitions

A disk is divided up into partitions which are subsections of the overall disk.
The kernel presents each partition as a [block device](Devices.md#Devices) as it
would with an entire disk.

The disk dedicates a small part of its contents to a **partition table**: this
defines the different partitions that comprise the total disk space.

## Viewing current partitions

Whenever you install a Linux distribution on a real or virtual machine, you must
partition the drive. There are three main tools to choose from: `parted`,
`g(raphical)parted`, `fdisk`.

For a top-level overview of your disks and their main partitions you can run
`lsblk` (_list block devices_):

```bash
$ lsblk

NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda           8:0    0 465.7G  0 disk
├─sda1        8:1    0   200M  0 part
└─sda2        8:2    0 465.4G  0 part /run/media/thomas/ganesh
nvme0n1     259:0    0 476.9G  0 disk
├─nvme0n1p1 259:1    0   488M  0 part
├─nvme0n1p2 259:2    0  27.9G  0 part /
└─nvme0n1p3 259:3    0 448.5G  0 part /home
```

We can use `parted -l` to view the partition table for the current machine:

```bash
Model: SKHynix_HFS512GDE9X081N (nvme)
Disk /dev/nvme0n1: 512GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  513MB   512MB   fat32              boot, esp
 2      513MB   30.5GB  30.0GB  ext4
 3      30.5GB  512GB   482GB   ext4
```

We can use `fdisk -l` to get slightly more info:

```bash
disk /dev/nvme0n1: 476.94 GiB, 512110190592 bytes, 1000215216 sectors
Disk model: SKHynix_HFS512GDE9X081N
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: gpt
Disk identifier: 08175E77-CB9F-C34A-9032-DF29A3F8F0FE

Device            Start        End   Sectors   Size Type
/dev/nvme0n1p1     2048    1001471    999424   488M EFI System
/dev/nvme0n1p2  1001472   59594751  58593280  27.9G Linux filesystem
/dev/nvme0n1p3 59594752 1000214527 940619776 448.5G Linux filesystem
```

## Standard Linux partitions

The two tools disclose that the main harddrive is `/dev/nvme0n1` (equivalent to
`sda` on older machines running Linux) and it has the standard three partitions:

- Boot partition (`/dev/nvme0n1p1`)
- Root dir (`/dev/nvme0n1p2`)
- Home dir (`/dev/nvme0n1p3`)

### Boot partition

- Takes up the smallest amount of space
- Contains the Linux kernel and the bootloader (GRUB, usually) and any other
  files required for booting.
- Once the BIOS has initialized the hardware components it hands control to the
  bootloader stored in this partition.
- The bootloader loads the kernel contained in its partition, into memory

### Root partition (`/`)

- This houses everything to do with the operation of the operating system apart
  from the initial booting process. Once the kernel is in memory it accesses the
  resources in the root partition to get the OS up and running. These resources
  include system libraries, utilities, system-wide configs and application
  software.

- The root partition is vital for the system's functionality. Without it, the
  system cannot boot or operate. It needs to be  
   large enough to accommodate the operating system, installed programs, and system
  libraries, but it doesn't need to store user data or  
   additional applications, which can be located on other partitions.

- This is the domain of the [superuser](User_Space.md#root-user-superuser). The
  part of the filesystem that you need sudo priveleges to access and where you
  manage users

### Home partition

- This is presented as `/home/`, i.e. that it is a descendent of `/`. But this
  is because the Linux file system is hierarchical. Typically `/home/` is
  usually its own partition.
- Separating user data and system data in this way protects user data during
  upgrades or reinstallation. Reinstalling or upgrading the OS can be done
  without affecting these files.
- Each user has their own directory off of `/home`, e.g `/home/thomas`.
- While the root partition (`/`) is essential for the operation of the OS,
  placing `/home` on a separate partition allows for better management of user
  data, enhancing the system's flexibility and the user's control over their own
  files, without compromising the integrity or performance of the OS. This
  approach exemplifies the Linux philosophy of giving the user control while
  maintaining a clear distinction between system  
  resources and user data.

## Types of partition table

In the Linux world there are two main types: MBR and GPT. The type of table used
determines how the OS boots. So although partition tables are also responsible
for the partitioning of non-bootable sectors of a disk, **they are distinguished
by the boot system they implement**. If we look at the output from `parted` and
`fdisk` above we see that the harddrive uses the GPT partition type.

#### Primary, extended and logical partitions

Most standard partition tables allow for primary, extended and logical
partitions. The primary partition is the part of the harddisk that contains the
operating system and is thus described as 'bootable' and may be called the 'boot
partition'. During the bootstrapping process this is injected into memory as the
[kernel](The_kernel.md).

The extended partition is basically everything other than the primary partition.
This is typically subdivided into other partitions that are called _logical_
partitions. This is because they physically reside in the same sector of the
disk (the extended partition) but are treated as virtual and independent disks.

In our example above:

- `/dev/nvme0n1p1` is the primary/boot partition
- `/dev/nvme0n1p2` and `/dev/nvme0n1p3` comprise the extended partition and by
  themselves are each logical partitions.

<dl>
  <dt>MBR</dt>
  <dd> 
    <ul>
      <li>Stands for Master Boot Record</li> 
      <li>Uses BIOS in the boot process</li> 
      <li>Can only works with disks up to 2TB in size</li> 
      <li>Only supports 4 primary partitions. This means the number of operating systems you install is limitied to this number.</li> 
      <li>This is the first 512 bytes of a storage device, preceding the first partition.</li>
    </ul> 
  </dd>
  <dt>GPT</dt>
  <dd>
  <ul>
      <li>Stands for GUID Partition Table </li>
      <li>Gradually replacing MBR</li>
      <li>Uses UEFI instead of BIOS</li>
      <li>As name indicates, every partition on disk has its own globally-unique identifier</li>
      <li>Vastly more partitions available than with MBR (dependent on operating system)</li>
      <li>Offers greater recovery options and anti-corruption safeguards</li> 
    </ul>
</dd>
</dl>

## Related notes

![Creating a Linux partition table](./Creating_a_Linux_partition_table.md)