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I just inherited a system and I am trying to understand it's partition table for the hard drive. (I'm new to this)

machine:~# fdisk -l /dev/sda

Disk /dev/sda: 250.0 GB, 250000000000 bytes
255 heads, 63 sectors/track, 30394 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: 0x00000080

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1       30064   241489048+  fd  Linux raid autodetect
/dev/sda2           30065       30394     2650725    5  Extended
/dev/sda5           30065       30394     2650693+  fd  Linux raid autodetect

Why does the numbering go from 1 to 2 to 5. "What is on" sda2 and sda5?

share|improve this question
For further reference you may be interested in Wikipedia's articles on MBR and extended (partition) boot records. – Michael Kjörling Jul 21 '13 at 22:23
up vote 6 down vote accepted

On Linux, traditional DOS-partitions will show up this way:

  • Partitions from 1 to 4 are primary partitions.
  • Partitions above 5 are logical partitions.

In the DOS-partitioning-scheme (this is not Linux-specific), if you want to use logical partitions you have to define a pointer within one of the primary partitions for these. At this pointer the BIOS will find further information.

This pointer (sda2 in your machine) shows in fdisk as id 5 "Extended" - it extends the partitioning-scheme to more than the default 4 partitions normally possible.

Now your system consists of two partitions:

One primary, bootable partition: sda1 (which was or is part of a linux-raid-array) and one logical partition: sda5 (which was or is part of a linux-raid-array).

There is no place left for additional partitions.

share|improve this answer
Technically it contains 2 primary partitions and one logical partition. – jordanm Jul 21 '13 at 4:12
@jordanm Right - I corrected my answer accordingly - I knew I was missing the right term here... – Nils Jul 21 '13 at 21:12

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