Disk Partitioning in Linux - GeeksforGeeks

25 Jan, 2021
Disk Partitioning is the process of dividing a disk into one or more logical areas, often known as partitions, on which the user can work separately. It is one step of disk formatting. If a partition is created, the disk will store the information about the location and size of partitions in the partition table. With the partition table, each partition can appear to the operating system as a logical disk, and users can read and write data on those disks. The main advantage of disk partitioning is that each partition can be managed separately.
Why we need it?
To upgrade Hard Disk (to incorporate new Hard Disk to the system)
Dual Booting (Multiple Operating Systems on the same system)
Efficient disk management
Ensure backup and security
Work with different File Systems using the same system
(For the purpose of demonstration Cent OS 7 and Vmware are used in the screenshots of the article.)
In order to successfully partition a disk and to make it useful, we need to ensure that, we have completed the below four steps, regardless of the Operating system and Hardware of the system.
Attach disk on the proper portCreate partitions in the diskCreate a file system on the partitionMounting the file systems 
Attach disk on the proper port
Create partitions in the disk
Create a file system on the partition
Mounting the file systems 
This step points to physically connecting the disk to the system. The below screenshot specifies the system configuration of my CentOS 7. 
Initial configuration of my system
It is clearly specified that the system is having only 20 GB of Hard Disk. After installing the necessary softwares and downloading some movies, I found that the system Hard Disk is almost completely used up. Now I will be having two options in front of me, either buy a new system with a higher Hard Disk capacity or to upgrade the existing one. Most of you will go for the second option, just like me, unless the system is very old. Let us upgrade the system with an additional 20 GB of Hard Disk.
In order to attach the new virtual Hard Disk in VMware, click on the “Edit virtual machine settings” link and choosing the Add option on the next window. 
Choose the Hard Disk option and move forward.
Choose the recommended disk type. (SCSI is recommended here since the Operating System that I am using is CentOS)
Complete the attaching of the disk by specifying the required size of Hard Disk needed and choosing the recommended selections.
After attaching the new virtual Hard Disk
The final configuration shows that our system is having a new Hard Disk of 20 GB size. The newly added Hard disk is of no use to our system unless we complete the remaining steps.
Power on the system and log in to the system. Ensure that you are logged in as root (or any user of the sudo group). Once the system UI came up, open the Terminal.  To view the available Hard Disks in our system, use the command lsblk or using cat /proc/partitions. Both commands will display the same results, but in different ways. 
lsblk
We can find that the system is having two disks -> sda and sdb. sda is our older Hard Disk. We can say so, as that disk is already in partitioned as sda1 and sda2. We can partition the disk using CLI as well as GUI. We will demonstrate CLI based partitioning in this article.
fdisk -l 
We found that the Hard Disk that we are going to partition can be found at /dev/sdb. Use the command
fdisk /dev/sdb
It will take us to a different console where we can use the partitioning specific commands. We will be concentrating more on the following commands (or flags).
m  -> help
p  -> print partition table
n  -> create new partition
d  -> delete partition
q  -> quit without writing
w  -> write to disk
While partitioning, we should be aware of certain factors. 
On a disk, we can have a maximum of four partitions
The partitions are of two typesPrimaryExtended
Primary
Extended
Extended partitions can have logical partitions inside it
Among the four possible partitions, the possible combinations areAll 4 primary partitions3 primary partitions and 1 extended partition
All 4 primary partitions
3 primary partitions and 1 extended partition
n
This will create a new partition. Specify the type of partition using the p for primary and e for extended
p
This will create a primary partition. The console will prompt for the number to be given to the partition. We can give any number from 1 to 4. Let me give 1. Then choose the starting position (cylinder) of partition 1. Press enter to start partitioning from the beginning of the disk. 
You can specify the size of the partition in two ways, either as the last cylinder number or by specifying the size directly. If we need the partition1 to be of 4 GB size (as a whole number), use
+4G 
Pressing enter will create our 1st partition successfully. Follow the same steps, until we create 4 partitions on our newly attached disk. 
We have created 3 primary partitions and an extended partition in the disk. The extended partition, as the name suggests, can be further divided into multiple logical partitions. Once 4 partitions are created, no more partitions can be created in the same disk. We can check whether we have done the partitioning in the right way by printing the partition table using the p command. If everything is as per the expectation, then write the changes to the disk using the w command, else use the q command to quit without writing. 
Computers use particular kinds of file systems to store and organize data on media, like Hard Disk, CD, DVD, etc. The commonly used Linux file systems are ext2, ext3, ext4, JFS, ReiserFS, XFS, FAT (usually in Windows OS ) and B-treeFS. Inorder to specify the file system to be used in each partition, we can use the mkfs (make file system) command.
mkfs.ext4 -j /dev/sdb1
What this command does is that it will make the first partition’s file system to be ext4 (format the partition to ext4). -j flag is used to allow/support journaling. It helps in throwing error into the journal, in case of system failure.
mkfs.fat /dev/sdb2
This command is used to format the 2nd partition available in /dev/sdb2 to the FAT file system. Even though we formatted the disks, it is of no use to us, unless we mount it on a directory.
Let us make three directories, for mounting the first, second, and third partition using the mkdir (make directory) command.
mkdir /mount1
mkdir /mount2
mkdir /mount3
Mounting the formatted partitions can be achieved using the mount command
mount /dev/sdb1 /mount1
mount /dev/sdb2 /mount2
mount /dev/sdb3 /mount3
The first part of the command is the keyword mount, followed by the partition and the directory to which the mounting is to be done. To view the disk details, we can use the df command. h flag helps to display the output in a human-readable format.
df -h
Unmounting a disk can be achieved by unmount command
unmount /dev/sdb2
All these mounting are temporary in nature. Once we reboot the system, mounting will be reverted. TO make it permanent, we must edit the File System Table of the Operating System. We should be highly careful while dealing with this file. A small error in this file can cause the system to be unbootable and can make the entire system to be useless. Let us open the file in any editor (I will be using the VI editor).
vi /etc/fstab
fstab(File System Table) file
Add our mounted file systems’ details in the file, in the order
mounted partition        [ space ]         directory      [ space ]           file system type          [ space ]          defaults         [ space ]         0            [ space ]             0 
Save the file and come back to the terminal. Mount the partitions permanently using the mount -a command 
mount -a
We can verify whether our partitions are available for our purposes, by visiting the root folder of the Operating System (since we have mounted the partitions on the mount1, mount2, mount3 directories in the root folder). We can also verify the existence of our newly created partitions using the lsblk command 
lsblk
We can find our partitions in the table, each of 4 GB size.
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