Image files of block devices

by | March 17, 2017

A few notes on manipulating image files of a Raspberry Pi filesystem.

  • How to mount the image file.
  • How to compress the image file.

Manipulate the image file

Interesting link on how to use loopback driver. After the file is attached to the loopback driver, it can be manipulated as every other block device.

https://softwarebakery.com/shrinking-images-on-linux

Fill empty space with zeros

For better compression! Use the command zerofree

[tommz@tommz-fedora Data 1T]$ sudo zerofree /dev/loop0p2

Benchmark

2.4 GB image of a Raspberry Pi SD card has been compressed with 7z. Then zerofree has been applied and the image was compressed again. Result:

$ ls -lh
684M img.7z
349M img.zerofree.7z

The file size has been reduced to one half.

Copy an image file to an SD Card

Using dd:

sudo dd bs=4M if=image.img of=/dev/sdX
sync

Note: Make sure that the partitions of the SD Card are not mounted!

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