This tutorial explains Linux “fdisk” command, options and its usage with examples.
Description:
Hard disks can be divided into one or more logical disks called partitions. This division is described in the partition table found in sector 0 of the disk.
This tutorial shows you how to actually partition your hard drive with the fdisk utility. Linux allows only 4 primary partitions. You can have a much larger number of logical partitions by sub-dividing one of the primary partitions. Only one of the primary partitions can be sub-divided.
Synopsis:
fdisk [-u] [-b sectorsize] [-C cyls] [-H heads] [-S sects] device
fdisk -l [-u] [device …]
fdisk -s partition ..
fdisk -v
OPTIONS
-b sectorsize
Specify the sector size of the disk. Valid values are 512, 1024, or 2048. (Recent kernels know the sector size. Use this only on old kernels or to override the kernel’s ideas.)
-C cyls
Specify the number of cylinders of the disk. I have no idea why anybody would want to do so.
-H heads
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.
-S sects
Specify the number of sectors per track of the disk. (Not the physical number, of course, but the number used for partition tables.) A reasonable value is 63.
-l
List the partition tables for the specified devices and then exit. If no devices are given, those mentioned in /proc/partitions (if that exists) are used.
-u
When listing partition tables, give sizes in sectors instead of cylinders.
-s partition
The size of the partition (in blocks) is printed on the standard output.
-v
Print version number of fdisk program and exit.
fdisk is started by typing (as root) fdisk device at the command prompt. The device is usually one of the following:
/dev/hda
/dev/hdb
/dev/sda
/dev/sdb
(/dev/hd[a-h] for IDE disks, /dev/sd[a-p] for SCSI disks, /dev/ed[a-d] for ESDI disks, /dev/xd[ab] for XT disks).
like :
$sudo fdisk /dev/sda Command (m for help): m Command action a toggle a bootable flag b edit bsd disklabel c toggle the dos compatibility flag d delete a partition l list known partition types m print this menu n add a new partition o create a new empty DOS partition table p print the partition table q quit without saving changes s create a new empty Sun disklabel t change a partitions system id u change display/entry units v verify the partition table w write table to disk and exit x extra functionality (experts only)
Examples :
1. Let’s create Four primary partitions
Decide on the size of your swap space and where it ought to go. Divide up the remaining space for the three other partitions.
I start fdisk from the shell prompt:
# fdisk /dev/hdb
which indicates that I am using the second drive on my IDE controller. When I print the (empty) partition table, I just get configuration information.
Command (m for help): p Disk /dev/hdb: 64 heads, 63 sectors, 621 cylinders Units = cylinders of 4032 * 512 bytes
I knew that I had a 1.2Gb drive, but now I really know: 64 * 63 * 512 * 621 = 1281982464 bytes. I decide to reserve 128Mb of that space for swap, leaving 1153982464. If I use one of my primary partitions for swap, that means I have three left for ext2 partitions. Divided equally, that makes for 384Mb per partition. Now I get to work.
Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-621, default 1): Using default value 1 Last cylinder or +size or +sizeM or +sizeK (1-621, default 621): +384M
Next, I set up the partition I want to use for swap:
Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 2 First cylinder (197-621, default 197): Using default value 197 Last cylinder or +size or +sizeM or +sizeK (197-621, default 621): +128M
Now the partition table looks like this:
Device Boot Start End Blocks Id System /dev/hdb1 1 196 395104 83 Linux /dev/hdb2 197 262 133056 83 Linux
I set up the remaining two partitions the same way I did the first. Finally, I make the first partition bootable:
Command (m for help): a Partition number (1-4): 1
And I make the second partition of type swap:
Command (m for help): t Partition number (1-4): 2 Hex code (type L to list codes): 82 Changed system type of partition 2 to 82 (Linux swap)
The end result:
Disk /dev/hdb: 64 heads, 63 sectors, 621 cylinders Units = cylinders of 4032 * 512 bytes Device Boot Start End Blocks Id System /dev/hdb1 * 1 196 395104+ 83 Linux /dev/hdb2 197 262 133056 82 Linux swap /dev/hdb3 263 458 395136 83 Linux /dev/hdb4 459 621 328608 83 Linux
Finally, I issue the write command (w) to write the table on the disk.
2. Let’s create Mixed primary and logical partitions
Create one use one of the primary partitions to house all the extra partitions. Then create logical partitions within it. Create the other primary partitions before or after creating the logical partitions.
I start fdisk from the shell prompt:
$ fdisk /dev/sda
which indicates that I am using the first drive on my SCSI chain. (See Section 2.1.)
First I figure out how many partitions I want. I know my drive has a 183Gb capacity and I want 26Gb partitions (because I happen to have back-up tapes that are about that size).
183Gb / 26Gb = ~7
so I will need 7 partitions. Even though fdisk accepts partition sizes expressed in Mb and Kb, I decide to calculate the number of cylinders that will end up in each partition because fdisk reports start and stop points in cylinders. I see when I enter fdisk that I have 22800 cylinders.
> The number of cylinders for this disk is set to 22800. There is
> nothing wrong with that, but this is larger than 1024, and could in
> certain setups cause problems with: 1) software that runs at boot
> time (e.g., LILO) 2) booting and partitioning software from other
> OSs (e.g., DOS FDISK, OS/2 FDISK)
So, 22800 total cylinders divided by seven partitions is 3258 cylinders. Each partition will be about 3258 cylinders long. I ignore the warning msg because this is not my boot drive
Since I have 4 primary partitions, 3 of them can be 3258 long. The extended partition will have to be (4 * 3258), or 13032, cylinders long in order to contain the 4 logical partitions.
I enter the following commands to set up the first of the 3 primary partitions (stuff I type is bold ):
Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-22800, default 1): Using default value 1 Last cylinder or +size or +sizeM or +sizeK (1-22800, default 22800): 3258
The last partition is the extended partition:
Partition number (1-4): 4 First cylinder (9775-22800, default 9775): Using default value 9775 Last cylinder or +size or +sizeM or +sizeK (9775-22800, default 22800): Using default value 22800
The result, when I issue the print table command is:
/dev/sda1 1 3258 26169853+ 83 Linux /dev/sda2 3259 6516 26169885 83 Linux /dev/sda3 6517 9774 26169885 83 Linux /dev/sda4 9775 22800 104631345 5 Extended
Next I segment the extended partition into 4 logical partitions, starting with the first logical partition, into 3258-cylinder segments. The logical partitions automatically start from /dev/sda5.
Command (m for help): n First cylinder (9775-22800, default 9775): Using default value 9775 Last cylinder or +size or +sizeM or +sizeK (9775-22800, default 22800): 13032
The end result is:
Device Boot Start End Blocks Id System /dev/sda1 1 3258 26169853+ 83 Linux /dev/sda2 3259 6516 26169885 83 Linux /dev/sda3 6517 9774 26169885 83 Linux /dev/sda4 9775 22800 104631345 5 Extended /dev/sda5 9775 13032 26169853+ 83 Linux /dev/sda6 13033 16290 26169853+ 83 Linux /dev/sda7 16291 19584 26459023+ 83 Linux /dev/sda8 19585 22800 25832488+ 83 Linux
Finally, I issue the write command (w) to write the table on the disk.
Note : To make the partitions usable, I will have to format each partition and then mount it.
Sanfoundry Global Education & Learning Series – 1000 Linux Tutorials.
- Check Linux Books
- Apply for Programming Internship
- Practice Programming MCQs
- Check Information Technology Books
