Synnefo » snf-image-creator

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By default snf-image-creator will run a number of system preparation

preparations on the snapshot of the media and will shrink the last partition

found, before extracting the image. Both can be disabled by specifying

*--no-sysprep* and *--no-shrink* respectively.

If *--print-sysprep* is defined, then snf-image-creator will only run the OS

detection part and will output the system preparation operation that would and

would not run during image creation. This behavior is, convenient because it

allows you to see the available system preparation tasks that you can enable or

disable with *-{enable,disable}-sysprep* options when you create a new image.

debian system, we get the following output:

====================

*snf-mkimage* receives the following options:

.. code-block:: console

   $ Usage: snf-mkimage [options] [<input_media>]

   Options:

     --version             show program's version number and exit

     -h, --help            show this help message and exit

     -l FILE, --logfile=FILE

                            log all messages to FILE

If the input media is not specified in the command line, then the user will be

asked to specify it in the first dialog box. After the input media is examined

and the program is initialized, the user is given the choice to run

*snf-mkimage* in *wizard* or *expert* mode.

Wizard mode

-----------

When *snf-mkimage* runs in *wizard* mode, the user is just asked to provide the

following basic information:

 * Name: A short name for image (ex. "Slackware")

 * Description: An one line description for the image (ex. "Slackware Linux 14.0 with KDE")

 * Account: An ~okeanos account e-mail

 * Token: A token corresponding to the account defined previously

For most users the functionality this mode provides should be sufficient.

Expert mode

-----------

Expert mode allows the user to have better control on the image creation

process. In the picture below the main menu can be seen:

.. image:: /snapshots/main_menu.png

In the *Customize* submenu the user can control:

 * The system preparation operations that will run during the image creation process

 * Whether the image will be shrunk or not

 * The properties associated with the image

 * Which configuration tasks will run during image deployment

In the *Register* submenu the user can provide:

 * The credentials to login to ~okeanos

 * A pithos filename for the uploaded diskdump image

 * A name for the image to be registered to ~okeanos with

By choosing the *Extract* menu entry the user can dump the image to the local

file system and finally, if the user selects *Reset*, the system will ignore

all changes made so far and will start the image creation process again.

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Suppose you want to create a new Ubuntu server image. Download the installation

disk from the Internet:

And install the Ubuntu system on this file:

After the installation finishes, become root, activate the virtual environment

you have installed snf-image-creator in, and use *snf-mkimage* to create and

upload the image:

in *Wizard* or *Expert* mode. Choose *Wizard*.

Things you need to pay attention on when creating images

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Para-virtualized drivers

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~Okeanos uses the VirtIO framework. The disk I/O controller and the Ethernet

cards on the VM instances are para-virtualized and need special VirtIO drivers.

Those drivers are included in the Linux Kernel mainline since version 2.6.25

and are shipped with all the popular Linux distributions. The problem is that

if those drivers are built as modules, they need to be preloaded using an

initial ramdisk, otherwise the VM will not be able to boot.

In the image creation demonstration above, we initially installed the Ubuntu

system on a a hard disk (ubuntu_hd.raw) that was para-virtualized (pay

attention on the *if=virtio* option of the kvm line). The Ubuntu installer

detected that the disk was paravirtualized and made sure the appropriate

drivers will be preloaded each time the system boots. In many distros this is

not the case. In Arch Linux for example, the user needs to manually add

*virtio_blk* and *virtio_pci* drivers in */etc/mkinitcpio.conf* and then

rebuild the initial ramdisk [#f1]_ to make the virtio drivers get preloaded

during boot.

Swap partitions

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

If you want your image to have a swap partitions, make sure this is the last

partition on the disk. If snf-image-creator detects a swap partition in the end

of the input media, it will remove the partition during shrinking and will save

enough information to be able to recreate it during image deployment. This will

make your image smaller and will speed up the deployment process.

.. rubric:: Footnotes

.. [#f1] https://wiki.archlinux.org/index.php/KVM#Paravirtualized_guests_.28virtio.29