Tuesday, 12 May 2015

How to Manage Hard Disk Partitions in Linux?

A logical disk/partition is a logical division on the hard disk. The partition table stores the info about various partitions on the disk. In Linux system, one partition is required as a root file system and the second partition as swap partition. In case of large disk sizes, often you can find a partition that stores the kernel image, data needed by BIOS at BIOS and some other auxiliary files. This partition is mounted on location /boot and carries the information required at boot time. 

About Fdisk: While Fdisk prints a partition table it matches the physical and logical start and end points. After verifying that those parameters are equal, the partition list is printed.

Fdisk is a text based utility to manage Linux partitions. It is also known as Partition table manipulator for Linux. Using the tool, you can perform various operations such as: viewing existing partitions, new partition creation, add a partition, partition deletion or modification. The utility let you create primary and logical partitions on the disk. The maximum allowed number of primary partitions is four; the number of logical partitions may vary according to disk size.

First create a disk partition, after that you can install your operating system. After you create a hard disk partition you should now use the format tool for formatting them. 

To make Linux partitions, you can use the Linux fdisk or Linux cfdisk program. Using the Fdisk utility, you can create four primary partitions. Open command prompt, run fdisk command. To make changes to the partition table, first you need to issue the write (w) command. The Fdisk option ‘w’ let you to write the new partition table and exit. If you want to quit without saving changes then use the fdisk command with q option.

For a hard disk larger than 512 megabytes (MB), you have two format options. You can choose either FAT16 or FAT32 file systems. Using the ‘File Allocation Table’ file system, data can be stored/accepted/retrieved in the hard disk. In case of FAT 16, the maximum allowed space for a drive letter is 2 GB. In case of FAT 32, the maximum size of drives can be up to 2 terabytes and minimum 512GB.

Below given are some options with the fdisk command:

1 View partition:

# fdisk -l: This command will let you view all partitions on all the hard disks connected to your system.
 The partition list will be displayed along with the device name.

If you want to view partitions on a specific device only then you can do by mentioning the device name along with fdisk -l command. 

e.g. # fdisk -l /dev/sda
Here /dev/sda is the harddisk name

The Fdisk option ‘p’ lets you print the partition table.

Run the Fdisk command:
# fdisk /dev/hdb

Command (m for help): p 
The above command will print the partition table.

2 Delete partition:

First delete all exiting partition using the command:
# fdisk -d

Now run the below command to create new partitions
# fdisk -n/dev/sda
Create a new partition: fdisk n 

3 fdisk –s: 

Let you view the size of partition
# fdisk -s /dev/sda7

-s partition let you print the partition size (in blocks) on the standard output. 

4 fdisk Expert Command f:

You can enable or disable the boot flag for a partition. 

While you delete partitions and create new ones. The partition order of the new partitions may get un ordered. You can ‘Fix the Partition Table Order’.

5 -b sectorsize: This option let you specify the sector size of the disk. 

6 -h: This option let you print help and then exit. 

7 -c: This option let you switch off DOS-compatible mode. 

8 -C cyls:  This option let you specify the number of cylinders of the disk. 

9 -H heads: This option let you specify the number of heads of the disk. (Not the physical number, of course, but the number used for partition tables.) Reasonable values are 255 and 16. 

10 -S sects:  This option let you specify the number of sectors per track of the disk. 

11 -u: This option let you view sizes in sectors instead of cylinders while listing partition table. 

12 –v: This option let you Print version number of fdisk program and exit.

Note: While using fdisk command, perform the actions carefully and prejudicially. Because once you format or delete a Linux partition using the command there is no direct way to get the data back. Whether its accidental or intentional deletion, if you want to get you lost Linux data back you will have to run some Linux recovery software that let you scan your drive for the lost partition data and save the recoverable items at your desired location.