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Question:Displaying partition information

Partition information is stored in a partition table on the disk. The table lists information about the start and end of each partition, information about its type, and whether it is marked bootable or not. To create and delete partitions, you edit the partition table using a program specially designed for the job. For the LPI exam, you need to know about the fdisk program, so that is what is covered here, although several other tools could be used. We will mention some at the end of this article.

The fdisk command with the -l option is used to list partitions. Add a device name, such as /dev/sda, if you want to look at the partitions on a particular drive. Note that partitioning tools require root access. Listing 2 shows the partitions on the primary hard drives of two of my systems.

Listing 2. Listing partitions with fdisk

[root@attic4 ~]# fdisk -l /dev/sda

Disk /dev/sda: 640.1 GB, 640135028736 bytes
255 heads, 63 sectors/track, 77825 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00064a1a

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1         127     1020096   83  Linux
/dev/sda2             128        1402    10241437+  82  Linux swap / Solaris
/dev/sda3   *       46340       56538    81920000   83  Linux
/dev/sda4            1403       46339   360956422    5  Extended
/dev/sda5            1403       10420    72437053+  83  Linux
/dev/sda6           10421       19344    71681998+  83  Linux
/dev/sda7           19345       28350    72340663+  83  Linux
/dev/sda8           28351       37354    72324598+  83  Linux
/dev/sda9           37355       46339    72171981   83  Linux

Partition table entries are not in disk order

[root@echidna ~]# fdisk -l /dev/sda

Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000de20f

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        9111    73184076    7  HPFS/NTFS
/dev/sda2            9634        9730      779152+  83  Linux
/dev/sda3            9731      116679   859067842+   5  Extended
/dev/sda5            9731       20917    89859546   83  Linux
/dev/sda6           20918       39644   150424596   83  Linux
/dev/sda7           39645       53905   114551451   83  Linux



    The header information shows the disk size and geometry. Most large disks using LBA have 255 heads per cylinder and 63 sectors per track, making a total of 16065 sectors, or 8225280 bytes per cylinder.
    In the second example, the first primary partition (/dev/sda1) is marked bootable (or active). This enables the standard DOS PC master boot record to boot the partition. This flag has no significance for the LILO or GRUB boot loaders. The first example uses GRUB as the boot loader, and the fact that /dev/sda3 is marked bootable is probably an accident of the history of my use of this drive.
    The Start and End columns show the starting and ending cylinder for each partition. These must not overlap and should generally be contiguous, with no intervening space.
    The Blocks column shows the number of 1K (1024 byte) blocks in the partition. For most disks in use at the time of writing, the sector size is 512 bytes, so the maximum number of blocks in a partition is therefore half of the product of the number of cylinders (End + 1 - Start) and the number of sectors per cylinder. A trailing + sign indicates that not all sectors in the partition are used.
    The Id field indicates the intended use of the partition. Type 82 is a Linux swap partition, and type 83 is a Linux data partition. There are approximately 100 different partition types defined. The second disk is shared between several operating systems, including Windows/XP, hence the presence of Windows NTFS (and possibly FAT32) partitions.
asked Sep 13, 2013 in LINUX by anonymous
edited Sep 12, 2013
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