Zero The Free Space¶

• Install zerofree:
  

  apt-get install zerofree
  

• Fill free space of the image with zero:
  

  zerofree /dev/sdb2
  

Acquiring The Image¶

• While modifying the stock image of Raspbian, I decided to take a backup image of my drive using dd:
  

  dd if=/dev/sdb of=modified-raspbian.img
  

• Then shrunk main partition image to the value I desired using gparted:
  

  gparted modified-raspbian.img
  

However the image of the entire drive left a lot of unallocated space left in the image. After searching online I found that all I needed to do was to use dd to extract just the raspbian image apart from the unallocated space. The parameter for dd that does this is count=.

Find Image Size Information¶

• Get the needed block information by running the following:
  

  fdisk -u -l modified-raspbian.img
  

  • Example output:
    

    Disk /dev/sdb: 8462 MB, 8462008320 bytes
    255 heads, 63 sectors/track, 1028 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: 0x5c0894d9
    
    Device Boot      Start         End      Blocks   Id  System
    /dev/sdb1   *           1           9       72261    e  W95 FAT16 (LBA)
    /dev/sdb2              10         103      755055   83  Linux
    

Trim The Image¶

• In the following example the last partition ends on 103, and the unit size is 8225280 bytes. So simply run command:
  

  dd if=modified-raspbian.img of=modified-raspbian-stripped.img bs=8225280 count=103
  

  • NOTE: I had problems with a couple of images being corrupt after this process, so I found that adding 1 to the count argument will correct this.
    

    dd if=modified-raspbian.img of=modified-raspbian-stripped.img bs=8225280 count=104
    

Resources¶

• http://serverfault.com/questions/446529/create-image-of-a-usb-drive-without-unallocated-partition