Usage

snf-image-creator comes in 2 variants:

  • snf-mkimage: A non-interactive command line program
  • snf-image-creator: A user-friendly dialog-based program

Both expect the input media as first argument. The input media may be a local file, a block device or “/” if you want to create an image out of the running system (see host bundling operation).

Non-interactive version

snf-mkimage receives the following options:

# snf-mkimage --help
Usage: snf-mkimage [options] <input_media>

Options:
  --version             show program's version number and exit
  -h, --help            show this help message and exit
  -a URL, --authentication-url=URL
                        use this authentication URL when uploading/registering
                        images
  --allow-unsupported   proceed with the image creation even if the media is
                        not supported
  -c CLOUD, --cloud=CLOUD
                        use this saved cloud account to authenticate against a
                        cloud when uploading/registering images
  --disable-sysprep=SYSPREP
                        prevent SYSPREP operation from running on the input
                        media
  --enable-sysprep=SYSPREP
                        run SYSPREP operation on the input media
  -f, --force           overwrite output files if they exist
  --host-run=SCRIPT     mount the media in the host and run a script against
                        the guest media. This option may be defined multiple
                        times. The script's working directory will be the
                        guest's root directory. BE CAREFUL! DO NOT USE
                        ABSOLUTE PATHS INSIDE THE SCRIPT! YOU MAY HARM YOUR
                        SYSTEM!
  --install-virtio=DIR  install VirtIO drivers hosted under DIR (Windows only)
  -m KEY=VALUE, --metadata=KEY=VALUE
                        add custom KEY=VALUE metadata to the image
  --no-snapshot         don't snapshot the input media. (THIS IS DANGEROUS AS
                        IT WILL ALTER THE ORIGINAL MEDIA!!!)
  --no-sysprep          don't perform any system preparation operation
  -o FILE, --outfile=FILE
                        dump image to FILE
  --print-metadata      print the detected image metadata
  --print-syspreps      print the enabled and disabled system preparation
                        operations for this input media
  --print-sysprep-params
                        print the defined system preparation parameters for
                        this input media
  --public              register image with the cloud as public
  -r IMAGENAME, --register=IMAGENAME
                        register the image with a cloud as IMAGENAME
  -s, --silent          output only errors
  --sysprep-param=SYSPREP_PARAMS
                        add KEY=VALUE system preparation parameter
  -t TOKEN, --token=TOKEN
                        use this authentication token when
                        uploading/registering images
  --tmpdir=DIR          create large temporary image files under DIR
  -u FILENAME, --upload=FILENAME
                      upload the image to the cloud with name FILENAME

Most input options are self-describing. If you want to save a local copy of the image you create, provide a filename using the -o option. To upload the image to the storage service of a cloud, provide valid cloud API access info (by either using a token and a URL with -t and -a respectively, or a cloud name with -c) and a remote filename using -u. If you also want to register the image with the compute service of the cloud, in addition to -u provide a registration name using -r. All images are registered as private. Only the user that registers the image can create VM’s out of it. If you want the image to be visible by other user too, use the –public option.

By default, before extracting the image, snf-mkimage will perform a number of system preparation operations on the snapshot of the media. You can disable this by specifying –no-sysprep.

You may use the –host-run option multiple times to define scripts that will run on the image’s locally mounted root directory before the image customization is performed. Be careful when using those. The scripts run on the host system without any jail protection. Use only relative paths.

If –print-sysprep is defined, the program will exit after printing a list of enabled and disabled system preparation operations applicable to this input media. The user can enable or disable specific syspreps, using -{enable,disable}-sysprep options. The user may specify those options multiple times.

Running snf-mkimage with –print-sysprep on a raw file that hosts an Ubuntu system, will print the following output:

# snf-mkimage --print-syspreps ubuntu.raw

snf-image-creator 0.7
===========================
Examining source media `ubuntu.raw' ... looks like an image file
Snapshotting media source ... done
Enabling recovery proc
Launching helper VM (may take a while) ... done
Inspecting Operating System ... ubuntu
Collecting image metadata ... done

Running OS inspection:
Checking if the media contains logical volumes (LVM)... no

Enabled system preparation operations:
    cleanup-tmp:
        Remove all files under /tmp and /var/tmp

    remove-swap-entry:
        Remove swap entry from /etc/fstab. If swap is the last partition
        then the partition will be removed when shrinking is performed. If the
        swap partition is not the last partition in the disk or if you are not
        going to shrink the image you should probably disable this.

    cleanup-cache:
        Remove all regular files under /var/cache

    cleanup-userdata:
        Delete sensitive user data

    cleanup-passwords:
        Remove all passwords and lock all user accounts

    cleanup-log:
        Empty all files under /var/log

    remove-persistent-net-rules:
        Remove udev rules that will keep network interface names persistent
        after hardware changes and reboots. Those rules will be created again
        the next time the image runs.

    use-persistent-block-device-names:
        Scan fstab & grub configuration files and replace all non-persistent
        device references with UUIDs.

    fix-acpid:
        Replace acpid powerdown action scripts to immediately shutdown the
        system without checking if a GUI is running.

    shrink:
        Shrink the last file system and update the partition table

Disabled system preparation operations:
    remove-user-accounts:
        Remove all user accounts with id greater than 1000

    cleanup-mail:
        Remove all files under /var/mail and /var/spool/mail


cleaning up ...

If you want the image to have all normal user accounts and all mail files removed, you should use –enable-sysprep option like this:

$ snf-mkimage --enable-sysprep cleanup-mail --enable-sysprep remove-user-accounts ...

Sysprep parameters are parameters used by some sysprep tasks. In most cases you don’t need to change their value. You can see the available sysprep parameters and the default values they have by using the –print-sysprep-params option. You can update their values by using the –sysprep-param option.

If the media is a Windows image, you can install or update its VirtIO drivers by using the –install-virtio option. With this option you can point to a directory that hosts a set of extracted Windows VirtIO drivers.

Dialog-based version

snf-image-creator receives the following options:

# snf-image-creator --help
Usage: snf-image-creator [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
  --tmpdir=DIR          create large temporary image files under DIR

If the input media is not specified in the command line, in the first dialog box the user will be asked to specify it:

_images/select_media.png

The user can select a file (regular or block device) or use the Bundle Host button to create an image out of the running system (see Host bundling operation).

After the input media is examined and the program is initialized, the user will be given the choice to run snf-image-creator in wizard or expert mode.

Wizard mode

When snf-image-creator runs in wizard mode, the user is just asked to provide the following basic information:

  • Cloud: The cloud account to use to upload and register the resulting image
  • Name: A short name for the image (ex. “Slackware”)
  • Description: An one-line description for the image (ex. “Slackware Linux 14.0 with KDE”)
  • VirtIO: A directory that hosts VirtIO drivers (for Windows images only)
  • Registration Type: Private or Public

After confirming, the image will be extracted, uploaded to the storage service and registered with the compute service of the selected cloud. The user will also be given the choice to keep a local copy of it.

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. The main menu can be seen in the picture below:

_images/main_menu.png

In the Customize sub-menu the user can control:

  • The installation of VirtIO drivers (only for Windows images)
  • The system preparation operations that will be applied on the media
  • The properties associated with the image
  • The configuration tasks that will run during image deployment

In the Register sub-menu the user can provide:

  • Which cloud account to use
  • A filename for the uploaded diskdump image
  • A name for the image to use when registering it with the storage service of the cloud, as well as the registration type (private or public)

By choosing the Extract menu entry, the user can dump the image to the local file system. Finally, if the user selects Reset, the system will ignore all changes made so far and will start the image creation process again.

Host bundling operation

As a new feature in v0.2, snf-image-creator can create images out of the host system that runs the program. This is done either by specifying / as input media or by using the Bundle Host button in the media selection dialog. During this operation, the files of the disk are copied into a temporary image file, which means that the file system that will host the temporary image needs to have a lot of free space (see large temporary files for more information).

Creating a new image

Suppose your host system is a Debian Wheezy and you want to create a new Ubuntu server image. Download the installation disk from the Internet:

$ wget http://ubuntureleases.tsl.gr/12.04.2/ubuntu-12.04.2-server-amd64.iso

Verify that it has been downloaded correctly:

$ echo 'a8c667e871f48f3a662f3fbf1c3ddb17  ubuntu-12.04.2-server-amd64.iso' > check.md5
$ md5sum -c check.md5

Create a 2G sparse file to host the new system:

$ truncate -s 2G ubuntu.raw

And install the Ubuntu system on this file:

$ sudo kvm -boot d -drive file=ubuntu.raw,format=raw,cache=none,if=virtio \
  -m 1G -cdrom ubuntu-12.04.2-server-amd64.iso

Warning

During the installation, you will be asked about the partition scheme. Don’t use LVM partitions. They are not supported by snf-image-creator.

You will be able to boot your installed OS and make any changes you want (e.g. install OpenSSH Server) using the following command:

$ sudo kvm -m 1G -boot c -drive file=ubuntu.raw,format=raw,cache=none,if=virtio

After you’re done, you may use snf-image-creator as root to create and upload the image:

$ sudo -s
# snf-image-creator ubuntu.raw

In the first screen you will be asked to choose if you want to run the program in Wizard or Expert mode. Choose Wizard.

_images/wizard.png

Then you will be asked to select a cloud and provide a name, a description and a registration type (private or public). Finally, you’ll be asked to confirm the provided data.

_images/confirm.png

Choosing YES will create and upload the image to your cloud account.

Working with different image formats

snf-image-creator is able to work with the most popular disk image formats. It has been successfully tested with:

  • Raw disk images
  • VMDK (VMware)
  • VHD (Microsoft Hyper-V) [1]
  • VDI (VirtualBox)
  • qcow2 (QEMU)

It can support any image format QEMU supports as long as it represents a bootable hard drive.

Limitations

Supported operating systems

snf-image-creator can fully function on input media hosting Linux, FreeBSD, OpenBSD, NetBSD and Windows (Server starting from 2008R2 and Desktop starting from 7) systems.

Logical Volumes

The program cannot work on input media that contain LVM partitions inside [2]. The input media may only contain primary or logical partitions.

Para-virtualized drivers

Most Synnefo deployments 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 the driver for the para-virtualized disk I/O controller is built as module, it needs to be preloaded using an initial ramdisk, otherwise the VM won’t be able to boot.

Many popular Linux distributions, like Ubuntu and Debian, will automatically create a generic initial ramdisk file that contains many different modules, including the VirtIO drivers. Others that target more experienced users, like Slackware, won’t do that [3]. snf-image-creator cannot resolve this kind of problems and it’s left to the user to do so. Please refer to your distribution’s documentation for more information on this. You can always check if a system can boot with para-virtualized disk controller by launching it with kvm using the if=virtio option (see the kvm command in the Creating a new image section).

For Windows the program supports installing VirtIO drivers. You may download the latest drivers from the Fedora Project.

Some caveats on image creation

Image partition schemes and shrinking

When image shrinking is enabled, snf-image-creator will shrink the last partition on the disk. If this is a swap partition, it will remove it, save enough information to recreate it during image deployment and shrink the partition that lays just before that. This will make the image smaller which speeds up the deployment process.

During image deployment, the last partition is enlarged to occupy the available space in the VM’s hard disk and a swap partition is added at the end if a SWAP image property is present.

Keep this in mind when creating images. It’s always better to have your swap partition placed as the last partition on the disk and have your largest partition (/ or /home) just before that.

Large temporary files

snf-image-creator may create large temporary files when running:

  • During image shrinking, the input media snapshot file may reach the size of the original media.
  • When bundling the host system, the temporary image file may became 10% larger than rest of the disk files altogether.

/tmp directory is not a good place for hosting large files. In many systems the contents of /tmp are stored in volatile memory and the size they may occupy is limited. By default, snf-image-creator will use a heuristic approach to determine where to store large temporary files. It will examine the free space under /var/tmp, the user’s home directory and /mnt and will pick the one with the most available space. The user may overwrite this behavior and indicate a different directory using the tmpdir option. This option is supported by both snf-image-creator and snf-mkimage.

Troubleshooting

Failures in launching libguestfs’s helper VM

The most common error you may get when using snf-image-creator is a failure when launching libguestfs‘s helper VM. libguestfs [4] is a library for manipulating disk images and snf-image-creator makes heavy use of it. Most of the time those errors have to do with the installation of this library and not with snf-image-creator itself.

The first thing you should do when troubleshooting this is to run the liguestfs-test-tool diagnostic tool. This tool gets shipped with the library to test if libguestfs works as expected. If it runs to completion successfully, you will see this near the end:

===== TEST FINISHED OK =====

and the test tool will exit with code 0.

If you get errors like this:

libguestfs: launch: backend=libvirt
libguestfs: launch: tmpdir=/tmp/libguestfseKwXgq
libguestfs: launch: umask=0022
libguestfs: launch: euid=0
libguestfs: libvirt version = 1001001 (1.1.1)
libguestfs: [00012ms] connect to libvirt
libguestfs: opening libvirt handle: URI = NULL, auth = virConnectAuthPtrDefault, flags = 0
libvirt: XML-RPC error : Failed to connect socket to '/var/run/libvirt/libvirt-sock': No such file or directory
libguestfs: error: could not connect to libvirt (URI = NULL): Failed to connect socket to '/var/run/libvirt/libvirt-sock': No such file or directory [code=38 domain=7]
libguestfs-test-tool: failed to launch appliance
libguestfs: closing guestfs handle 0x7ff0d44f8bb0 (state 0)
libguestfs: command: run: rm
libguestfs: command: run: \ -rf /tmp/libguestfseKwXgq

it means that libguestfs is configured to use libvirt backend by default but the libvirt deamon is not running. You can either start libvirt deamon (providing instructions on how to do this is out of the scope of this tutorial) or change the default backend to direct by defining the LIBGUESTFS_BACKEND variable like this:

# export LIBGUESTFS_BACKEND=direct

If you run the libguestfs-test-tool, the command should finish without errors. Do the same every time before running snf-image-creator.

If you get errors on febootstrap-supermin-helper like this one:

febootstrap-supermin-helper: ext2: parent directory not found: /lib:
File not found by ext2_lookup
libguestfs: error: external command failed, see earlier error messages
libguestfs-test-tool: failed to launch appliance
libguestfs: closing guestfs handle 0x7b3160 (state 0)

you probably need to update the supermin appliance (just once). On Debian and Ubuntu systems you can do it using the command below:

# update-guestfs-appliance

Footnotes

[1]http://technet.microsoft.com/en-us/library/bb676673.aspx
[2]http://sourceware.org/lvm2/
[3]http://mirrors.slackware.com/slackware/slackware-14.0/README.initrd
[4]http://libguestfs.org/