The fdisk command on Linux Explained

The fdisk command is a standard disk management tool on Linux. This tutorial explains how to use it to create new partitions and manage or delete existing partitions on Linux.

Select a blank hard disk or the hard disk on which you want to create or manage partitions and specify its name as an argument to the fdisk command. You need to provide the full path with the disk name. For example, if you want to create or manage partitions on the disk sda, use the following command.

#fdisk /dev/sda

You can use the lsblk command to list the attached hard disks and their partition information.

The fdisk utility reads the partition information from the specified disk and provides a command prompt to manage the disk.

It uses letters as commands. For example, it keeps all changes in memory until we instruct it to save them. We use the letter w to save the changes. It interrupts the letter w as the write command.

We use the p (print) command to print the current partition information.

As we can see in the above output, this disk currently has no partitions.

MBR firmware

This command creates partitions for MBR firmware. MBR firmware supports a maximum of 14 partitions. It uses a concept of primary, extended, and logical partitions. It supports a maximum of four primary partitions. You must convert the last primary partition into the extended partition if you need more partitions. Inside the extended partition, you can create eleven logical partitions. The extended partition works as a container. It stores only logical partitions. We cannot use it to save data.

Creating new partitions

The n (new) command creates a new partition. It starts a new command prompt. On this prompt, we need to specify the following information in the sequence: partition type, partition number, first sector, and last sector or partition size.

Let us create two primary partitions of 500 MB.

Let us create one more primary partition of 1 GB.

We have created three primary partitions. Now, we can create one more primary partition or an extended partition.

Let us create an extended partition.

Inside the extended partition, we can create logical partitions. We can create a maximum of 11 logical partitions.

Let us create two logical partitions. Use 1GB of disk space for the first partition.

Use the remaining disk space for the second partition.

To verify partitions, use the p command.

Changing partition type

By default, the fdisk command creates standard Linux partitions. It supports many other partition types as well. To view a complete list of all supported partition types, you can use the l command. The l command lists all supported partition types with their hexacode.

To change the partition type, we use the t command. The t command needs two arguments: partition number and hexacode. By default, it changes the type of the last partition. To change the type of any other partition, specify its number as an argument. After the partition number, specify the hexacode of the type you want to use.

Let us change the type of the last partition to LVM.

The fdisk command keeps all changes we make in the RAM until we use the w (write) command. Use the w command to save and apply the changes.

The kernel reads the partition information at the boot time. It does not actively monitor this information on the running system. If we change to this information, the kernel will learn about the changes at the next boot. If we want to update the kernel about this change without rebooting the system, we must use the partprobe command. This command forces the kernel to reread the partition information.

To verify the new partitions, we can use the lsblk command again.

After creating a partition, you must create a file system on it and mount it to the Linux file system before you can use it to save data. If you mount a partition, you must un-mount it before deleting it.

Deleting partitions

To delete a partition, run the fdisk command and specify the disk's name that contains the partition as an argument.

On the fdisk command prompt, we use the d command to delete a partition. The d command needs the partition number. By default, it selects the last partition.

Let us delete the partitions we created in this exercise.

Use the w command to save the updated partition information.

Run the partprobe command to update the kernel and use the lsblk command again to verify the delete operation.

As we can see in the above output, the partitions we made in this exercise have gone.

Conclusion

The fdisk command is a powerful tool for managing disk partitions on Linux. It enables users to create, modify, and delete partitions effectively through a command-line interface. By following the steps outlined in this tutorial, you can confidently manage both MBR and extended partitions and create logical partitions as needed.