Creating a Linux partition table

Creating a partition table

To demonstrate the process of partitioning a harddrive I am going to repartition an external SATA drive as if it were being primed for a fresh Linux install.

Let’s take a look at the disk in its current form:

$ fdisk -l

  Disk /dev/sda: 465.74 GiB, 500079525888 bytes, 976717824 sectors
  Disk model: My Passport 071Aumount /dev/sda2
  Disklabel type: gpt
  Disk identifier: 9993F1BB-626C-485F-8542-3CC73BB40953

  Device      Start       End   Sectors   Size Type
  /dev/sda1      40    409639    409600   200M EFI System
  /dev/sda2  409640 976455639 976046000 465.4G Apple HFS/HFS+

(This disk was previously used as a backup disk for MacOS so in addition to the extended partition which has a proprietary file system type (Apple HFS) it has a primary partition which would load the recovery OS. In contrast to my main harddrive this uses the standard SCSI prototcol and thus the partitions are prepended with sda.)

1. Unmount existing partitions

umount /dev/sda1
umount /dev/sda2

2. Deleting the existing partitions

# Load the disk into fdisk
$ sudo fdisk /dev/sda
Command (m for help): d
Partition number (1,2, default 2): 1
Partition 1 has been deleted.
Command (m for help): d
Selected partition 2
Partition 2 has been deleted.

# Verify deletion with p(rint) command
Command (m for help): p
Disk /dev/sda: 465.74 GiB, 500079525888 bytes, 976717824 sectors
Disk model: My Passport 071A
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: 9993F1BB-626C-485F-8542-3CC73BB40953

# Write the changes to disk with w(rite)
w

# Check execution:
$ lsblk

NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda           8:0    0 465.7G  0 disk

So now the disk has no partitions, just the physical disk space and no mountpoints. We are ready to re-partition.

3. Re-partition the disk

We are going to create a GPT partition table

$ sudo fdisk /dev/sda
Command (m for help): g
Created a new GPT disklabel (GUID: E316B1A9-6F73-FB41-8CBB-FA4E3C448F2B).

Command (m for help): n
Partition number (1-128, default 1):
First sector (2048-976717790, default 2048):

# Just press enter here

# The last sector is where we put the actual size we want for the partition
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-976717790, default 976715775): +100G
Created a new partition 1 of type 'Linux filesystem' and of size 100 GiB.

# For the second and final partition, we follow the same steps but don't add a partition size, since it will default to what is left.

Command (m for help): n
Partition number (2-128, default 2):
First sector (209717248-976717790, default 209717248):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (209717248-976717790, default 976715775):

Created a new partition 2 of type 'Linux filesystem' and of size 365.7 GiB.

# Check the partitions with p(rint)
Command (m for help): p
Disk /dev/sda: 465.74 GiB, 500079525888 bytes, 976717824 sectors
Disk model: My Passport 071A
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: 92739978-F7D2-5042-9758-C1429B5C8E11

Device         Start       End   Sectors   Size Type
/dev/sda1       2048 209717247 209715200   100G Linux filesystem
/dev/sda2  209717248 976715775 766998528 365.7G Linux filesystem

# Then write with w
Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

We can now confirm our new partitions:

$ lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda           8:0    0 465.7G  0 disk
├─sda1        8:1    0   100G  0 part
└─sda2        8:2    0 365.7G  0 part

Naming a partition

By default each partition will have its GUID as its name, but you can add a human friendly name with:

sudo e2label /dev/sda1 my_human_name

Whilst we have created our partitions we cannot yet mount them. This is because we have not yet set up a filesystem on the partitions. This is the next step.

Related notes