diskim

This description assumes that a release is used. If you clone diskim you must build it locally.

Create disk images for VMs without root or sudo.

./diskim.sh mkimage --image=/tmp/hd.img /path/to/your/source/dir

This will create a qcow2 disk image with the contents from your source dir.

An important feature of diskim is that you can specify multiple sources for the image;

./diskim.sh mkimage /path/to/your/base/system \
  /path/to/ip/tools.tar /path/to/your/application ...

The sources can be a directory, a tar-file or a cpio file. The sources will be copied in order to your image.

Dependencies

Diskim will start a VM so kvm must be installed on the machine. On Ubuntu do something like;

kvm-ok
# If needed;
sudo apt install qemu-kvm
sudo usermod -a -G kvm $USER

Quick start

Create an image from the initrd used by diskim itself. Since diskim is implemented using a disk image you may use it as an example;

./diskim.sh mkimage --image=/tmp/hd.img ./tmp/initrd.cpio

Now you can start a kvm using the image with;

./diskim.sh kvm --image=/tmp/hd.img root=/dev/vda
# Or in an xterm;
./diskim.sh xkvm --image=/tmp/hd.img root=/dev/vda

To terminate do poweroff in the VM console or do;

./diskim.sh kill_kvm

Build

Please see the build instruction.

Test and examples

See the test instruction. A VirtualBox example is included.

Advanced operation and utilities

Set default options

If you plan to work on the same image for some time it is convenient to set the $__image variable instead of specifying the parameter all the time;

export __image=/tmp/hd.img
./diskim.sh mkimage /path/to/your/source/dir

Custom tar

Very often you want to include files that are not in your directory, wor instance a tool from your host (e.g. strace). In diskim you can create an executable script called tar in your directory and diskim will use that script to create a tar-file that will be unpacked on you image. Please see test/bootable/tar for an example.

Bootable image

Diskim uses the extlinux boot loader to create bootable images. Use the --bootable option. Note that you must install a Linux kernel and extlinux.conf on the image. Please see test/bootable/tar for an example.

./diskim.sh mkimage --image=/tmp/hd.img --bootable \
  $DISKIM_WORKSPACE/initrd.cpio ./test/bootable

Test with;

qemu-system-x86_64 -enable-kvm --nographic -smp 2 \
  -drive file=/tmp/hd.img,if=virtio,index=1,media=disk

Create an image manually

If you don't like diskim or need some feature not supported you may want to create an image manually. It is really quite easy, but you will need sudo.

First create an empty file;

truncate /tmp/hd.img --size=2G

Note that the file is "sparse" it looks like a 2G file but it is really empty and takes 0 (zero) byte on disk;

> ls -lsh /tmp/hd.img
0 -rw-rw-r-- 1 lgekman lgekman 2,0G maj 22 17:05 /tmp/hd.img

Now format the image;

mke2fs -t ext3 -F /tmp/hd.img

To copy files into the image you can loopback mount it, but that requires sudo;

mkdir /tmp/mnt
sudo mount -t ext3 -o loop /tmp/hd.img /tmp/mnt
sudo chmod 777 /tmp/mnt
# (copy files to /tmp/mnt)

Before unmounting you can make the image bootable with extlinux;

mkdir /tmp/mnt/boot
# (copy a kernel and extlinux.conf to /tmp/mnt/boot)
sudo extlinux -i /tmp/mnt/boot

Unmount the image;

sudo umount /tmp/mnt

Now you can convert the raw image to other formats if you like, for instance qcow2;

qemu-img convert -O qcow2 /tmp/hd.img /tmp/hd.qcow2