Using fdisk in Linux

fdisk is a very powerful tool. And as a system administrator you should know how to

use this tool effectively and efficiently without causing harm to data. This tool will

save you a lot of time during installation and during normal system operation, both.

To check the partition list, use fdisk -l:

[root@mainserver /]# fdisk -l

Disk /dev/hda: 255 heads, 63 sectors, 4867 cylinders

Units = cylinders of 16065 * 512 bytes

 

The * in Boot column shows the active or boot partition, in this case it is /dev/hda2 or 2nd primary partition on FAT32. The Id column contains the partition file system type in hexadecimal format. Also the command will list all the hard disks attached to the system and will display all the partitions in each hard disk.

While creating partitions, it should be noted that at one time there can be a maximum of four primary (with no extended) partitions on one hard drive, numbered 1 to 4. Also there can be only one extended (with max three primary) partition on one hard disk. You can create as many partitions in extended as you want, numbered 5 and above. So in the above example output of the command, fdisk -l, you can see three primary partitions, numbered /dev/hda1 to /dev/hda3 and an extended partition (considered a special type of primary partition) /dev/hda4, defined in hard disk /dev/hda, which is the primary master hard disk on this system. This extended partition contains four logical partitions(as many windows users call / identify them), numbered /dev/hda5 to /dev/hda8.

The IDE devices are numbered using the following scheme :

Primary master/dev/hda Primary slave/dev/hdb Secondary master/dev/hdc Secondary slave/dev/hdd

Disk /dev/hda: 255 heads, 63 sectors, 4867 cylinders

Units = cylinders of 16065 * 512 bytes

To modify partitions use fdisk in interactive mode. You have to type in the hard disk device id as a parameter. Type the following command and press m to get a list of available commands.

[root@mainserver /]# fdisk /dev/hdc

The number of cylinders for this disk is set to 4867. 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., old versions of LILO) 2) booting and partitioning software from other OSs    (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): m Command action    atoggle a bootable flag    bedit bsd disklabel    ctoggle the dos compatibility flag    ddelete a partition    llist known partition types    mprint this menu    nadd a new partition    ocreate a new empty DOS partition table    pprint the partition table    qquit without saving changes    screate a new empty Sun disklabel    tchange a partition's system id    uchange display/entry units    vverify the partition table    wwrite table to disk and exit    xextra functionality (experts only)

Command (m for help):