Bering-uClibc 4.x - User Guide - Appendices - Working with Disk Image Files
Appendices - Working with Disk Image Files | ||
---|---|---|
Prev | Bering-uClibc 4.x - User Guide | Next |
Contents
Introduction
Under some circumstances, especially when developing and testing Bering-uClibc 4.x using a Virtual PC, it can be convenient to work with a "virtual" disk drive image rather than "physical" disk drive media. The following notes provide hints and tips on how to do this using various standard Linux tools.
Many readers will already be familiar with mounting disk image files (in particular ISO9660 .iso
image files) using a "loopback device", for example with commands like:
mount -o loop image.iso /mnt/
The main complication arises when disk partitions are involved, since it is typically necessary to work with the complete disk image at one level, in order to create and manipulate the partitions, and then to work with individual partition images at another level in order to work with files in those partitions. The problem is that the partitions start at different places within the overall disk image file and it can be difficult to work out what "offset" to use when loop-mounting individual partitions. The kpartx utility provides a neat solution to this problem.
The commands on this page were developed and tested on Fedora 15. Some commands must be run as user root (prefixed with '#') whereas other commands can be run as any user (prefixed with '$').
Raw Hard Disk Image File
Create the Blank Image File
There are several ways of creating an empty disk image file. One of the easiest is to use the QEMU image manipulation utility:
$ qemu-img create -f raw sda.raw 1G
Work with the Whole Disk Image
The whole disk image cannot be "mounted" since it doesn't directly contain a filesystem. It can however be mapped as a loopback device:
# losetup /dev/loop0 sda.raw
At this point it is possible to manipulate the disk partition table using the usual tools: cfdisk, parted etc. For example:
# parted /dev/loop0 print
Once the disk image contains a partition table use the kpartx tool to map the partitions:
# kpartx -a /dev/loop0
This creates additional device files in the /dev/mapper/
directory corresponding to each Partition within the disk image. For example, if there are two partitions:
$ ls /dev/mapper/loop* /dev/mapper/loop0p1 /dev/mapper/loop0p2
Work with a Disk Partition Image
If not already formatted each disk partition needs a filesystem. For example:
# mkfs.vfat /dev/mapper/loop0p1
Once formatted the disk partition can be mounted:
# mount /dev/mapper/loop0p1 /mnt/
The files on the partition can then be manipulated using all the usual tools.
Unmounting
When finished:
# umount /mnt/ # kpartx -d /dev/loop0 # losetup -d /dev/loop0
Further information at:
Prev | Up | Next |