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Partitioning with fdisk

This section 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.

Examples:
  1. Four primary partitions
  2. Mixed primary and logical partitions

Notes about fdisk: fdisk is started by typing (as root) "fdisk device" at the command prompt. "device" might be something like /dev/hda or /dev/sda. The basic fdisk commands you need are:
p print the partition table
n create a new partition
d delete a partition
q quit without saving changes
w write the new partition table and exit

Changes you make to the partition table do not take effect until you issue the write (w) command. Here is a sample partition table:
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       184    370912+  83  Linux
/dev/hdb2           185       368    370944   83  Linux
/dev/hdb3           369       552    370944   83  Linux
/dev/hdb4           553       621    139104   82  Linux swap
The first line shows the geometry of your hard drive. It may not be physically accurate, but you can accept it as though it were. The hard drive in this example is made of 32 double-sided platters with one head on each side (probably not true). Each platter has 621 concentric tracks. A 3-dimensional track (the same track on all disks) is called a cylinder. Each track is divided into 63 sectors. Each sector contains 512 bytes of data. Therefore the block size in the partition table is 64 heads * 63 sectors * 512 bytes er...divided by 1024. (See Section 6 for discussion on problems with this calculation.)
The start and end values are cylinders. The first cylinder (0) is reserved for information about the drive layout.

  1. Four primary partitions

    2. The overview:Decide on the size of your swap space and where it ought to go. Divide up the remaining space for the three other partitions.

    Example:

    I start fdisk from the shell prompt:

    # fdisk /dev/hdb
    which indicates that I am using the second drive on my IDE controller. (See device names.) Now I need to plan my layout. In this example, I want to use only primary partitions for my linux partitions and my swap space. 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)      
Command (m for help): p
    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.

    How to activate swap space
    How to format partitions
    How to mount partitions

  2. Mixed primary and logical partitions

    3. The overview: 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.

    Example:

    I start fdisk from the shell prompt:

    # fdisk /dev/sda
    which indicates that I am using the first drive on my SCSI chain. (See device names.)

    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): <RETURN>
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): <RETURN>
Using default value 9775
Last cylinder or +size or +sizeM or +sizeK (9775-22800, default 22800): <RETURN>
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): <RETURN>
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. To make the partitions usable, I will have to format each partition and then mount it.

    Submitted Examples

     Valkor

    I'd like to submit my partition layout, because it works well with any disrtibution of Linux (even big RPM based ones). I have one hard drive that ... is 10 gigs, exactly. Windows can't see above 9.3 gigs of it, but Linux can see it all, and use it all. It also has much more than 1024 cylenders.

    /dev/hda1 /boot (15 megs)
    /dev/hda2 windows 98 partition (2 gigs)
    /dev/hda3 extended (N/A)
    /dev/hda5 swap space (64 megs)
    /dev/hda6 /tmp (50 megs)
    /dev/hda7 / (150 megs)
    /dev/hda8 /usr (1.5 gigs)
    /dev/hda9 /home (rest of drive)

    I test new kernels for the USB mass storage, so that explains the large /boot partition. I install LILO into the MBR, and by default I boot windows (I'm not the only one to use this computer).

    I also noticed that you don't have any REAL examples of partition tables, and for newbies I HIGHLY suggest putting quite a few up. I'm freshly out of the newbie stage, and partitioning was what messed me up the most.

    -------------------------------------------------------------------------

    © 2000 Karsten M. Self (kmself@ix.netcom.com)
    Last updated 2000/12/04 19:30:54

    My own current filesystems and utilization

    Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/root               152247     51652     92733  36% /
/dev/sdb5               101089      3737     92133   4% /tmp
/dev/sdb6               303344    233213     54470  82% /var
/dev/hda5               495960    118804    351556  26% /var/spool/news
/dev/sda5              1209572   1038000    110128  91% /usr
/dev/sdb7              1517920   1240280    200532  87% /usr/local
/dev/hda8               253775    156210     84463  65% /usr/doc
/dev/hda6               249871    135434    101537  58% /usr/src
/dev/sda7               585008    352004    203288  64% /home
/dev/hda2              1007992    699120    257668  74% /mnt/misc1
/dev/hdc                 47808     47808         0 100% /mnt/cdrom

    Partition tables

    Disk /dev/hda: 128 heads, 63 sectors, 620 cylinders
Units = cylinders of 8064 * 512 bytes

   Device Boot    Start       End    Blocks   Id  System
/dev/hda1   *         1        39    157216+   6  FAT16
/dev/hda2            40       293   1024128   83  Linux
/dev/hda3           294       332    157248   83  Linux
/dev/hda4           333       620   1161216    5  Extended
/dev/hda5           333       459    512032+  83  Linux
/dev/hda6           460       523    258016+  83  Linux
/dev/hda7           524       555    128992+  83  Linux
/dev/hda8           556       620    262048+  83  Linux



Disk /dev/sda: 255 heads, 63 sectors, 261 cylinders
Units = cylinders of 16065 * 512 bytes

   Device Boot    Start       End    Blocks   Id  System
/dev/sda1             1        17    136521   82  Linux swap
/dev/sda2            18       261   1959930    5  Extended
/dev/sda5            18       170   1228941   83  Linux
/dev/sda6           171       187    136521   82  Linux swap
/dev/sda7           188       261    594373+  83  Linux



Disk /dev/sdb: 255 heads, 63 sectors, 261 cylinders
Units = cylinders of 16065 * 512 bytes

   Device Boot    Start       End    Blocks   Id  System
/dev/sdb1             1        17    136521   82  Linux swap
/dev/sdb2            18       261   1959930    5  Extended
/dev/sdb5            18        30    104391   83  Linux
/dev/sdb6            31        69    313236   83  Linux
/dev/sdb7            70       261   1542208+  83  Linux



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