Building An Image ================= Now that you have diskimage-builder properly :doc:`installed ` you can get started by building your first disk image. VM Image -------- Our first image is going to be a bootable vm image using one of the standard supported distribution :doc:`elements <../elements>` (Ubuntu or Fedora). The following command will start our image build (distro must be either 'ubuntu' or 'fedora'): :: disk-image-create vm This will create a qcow2 file 'image.qcow2' which can then be booted. Elements -------- It is important to note that we are passing in a list of :doc:`elements <../elements>` to disk-image-create in our above command. Elements are how we decide what goes into our image and what modifications will be performed. Some elements provide a root filesystem, such as the ubuntu or fedora element in our example above, which other elements modify to create our image. At least one of these 'distro elements' must be specified when performing an image build. It's worth pointing out that there are many distro elements (you can even create your own), and even multiples for some of the distros. This is because there are often multiple ways to install a distro which are very different. For example: One distro element might use a cloud image while another uses a package installation tool to build a root filesystem for the same distro. Other elements modify our image in some way. The 'vm' element in our example above ensures that our image has a bootloader properly installed. This is only needed for certain use cases and certain output formats and therefore it is not performed by default. Output Formats -------------- By default a qcow2 image is created by the disk-image-create command. Other output formats may be specified using the `-t ` argument. Multiple output formats can also be specified by comma separation. The supported output formats are: * qcow2 * tar * tgz * squashfs * vhd * docker * raw Disk Image Layout ----------------- The disk image layout (like number of images, partitions, LVM, disk encryption) is something which should be set up during the initial image build: it is mostly not possible to change these things later on. There are currently two defaults: * When using the ``vm`` element, an element that provides ``block-device`` should be included. Available ``block-device-*`` elements cover the common case of a single partition that fills up the whole disk and used as root device. Currently there are MBR, GPT and EFI versions. For example, to use a GPT disk you could build with :: disk-image-create -o output.qcow vm block-device-gpt ubuntu-minimal * When not using the ``vm`` element a plain filesystem image, without any partitioning, is created. If you wish to customise the top-level ``block-device-default.yaml`` file from one of the ``block-device-*`` elements, set the environment variable `DIB_BLOCK_DEVICE_CONFIG`. This variable must hold YAML structured configuration data or be a ``file://`` URL reference to a on-disk configuration file. There are a lot of different options for the different levels. The following sections describe each level in detail. General Remarks +++++++++++++++ In general each module that depends on another module has a `base` element that points to the depending base. Also each module has a `name` that can be used to reference the module. Tree-Like vs. Complete Digraph Configuration ++++++++++++++++++++++++++++++++++++++++++++ The configuration is specified as a digraph_. Each module is a node; a edge is the relation of the current element to its `base`. Because the general digraph_ approach is somewhat complex when it comes to write it down, the configuration can also be given as a tree_. .. _digraph: https://en.wikipedia.org/wiki/Directed_graph .. _tree: https://en.wikipedia.org/wiki/Tree_(graph_theory) Example: The tree like notation .. code-block:: yaml mkfs: name: root_fs base: root_part mount: mount_point: / is exactly the same as writing .. code-block:: yaml mkfs: name: root_fs base: root_part mount: name: mount_root_fs base: root_fs mount_point: / Non existing `name` and `base` entries in the tree notation are automatically generated: the `name` is the name of the base module prepended by the type-name of the module itself; the `base` element is automatically set to the parent node in the tree. In mostly all cases the much simpler tree notation can be used. Nevertheless there are some use cases when the more general digraph notation is needed. Example: when there is the need to combine two or more modules into one new, like combining a couple of physical volumes into one volume group. Tree and digraph notations can be mixed as needed in a configuration. Limitations +++++++++++ To provide an interface towards the existing elements, there are currently three fixed keys used - which are not configurable: * `root-label`: this is the label of the block device that is mounted at `/`. * `image-block-partition`: if there is a block device with the name `root` this is used else the block device with the name `image0` is used. * `image-path`: the path of the image that contains the root file system is taken from the `image0`. Level 0 +++++++ Module: Local Loop .................. This module generates a local image file and uses the loop device to create a block device from it. The symbolic name for this module is `local_loop`. Configuration options: name (mandatory) The name of the image. This is used as the name for the image in the file system and also as a symbolic name to be able to reference this image (e.g. to create a partition table on this disk). size (optional) The size of the disk. The size can be expressed using unit names like TiB (1024^4 bytes) or GB (1000^3 bytes). Examples: 2.5GiB, 12KB. If the size is not specified here, the size as given to disk-image-create (--image-size) or the automatically computed size is used. directory (optional) The directory where the image is created. Example: .. code-block:: yaml local_loop: name: image0 local_loop: name: data_image size: 7.5GiB directory: /var/tmp This creates two image files and uses the loop device to use them as block devices. One image file called `image0` is created with default size in the default temp directory. The second image has the size of 7.5GiB and is created in the `/var/tmp` folder. Level 1 +++++++ Module: Partitioning .................... This module generates partitions on existing block devices. This means that it is possible to take any kind of block device (e.g. LVM, encrypted, ...) and create partition information in it. The symbolic name for this module is `partitioning`. MBR *** It is possible to create primary or logical partitions or a mix of them. The numbering of the primary partitions will start at 1, e.g. `/dev/vda1`; logical partitions will typically start with `5`, e.g. `/dev/vda5` for the first partition, `/dev/vda6` for the second and so on. The number of logical partitions created by this module is theoretical unlimited and it was tested with more than 1000 partitions inside one block device. Nevertheless the Linux kernel and different tools (like `parted`, `sfdisk`, `fdisk`) have some default maximum number of partitions that they can handle. Please consult the documentation of the appropriate software you plan to use and adapt the number of partitions. Partitions are created in the order they are configured. Primary partitions - if needed - must be first in the list. GPT *** GPT partitioning requires the ``sgdisk`` tool to be available. Options ******* There are the following key / value pairs to define one partition table: base (mandatory) The base device to create the partitions in. label (mandatory) Possible values: 'mbr', 'gpt' Configure use of either the Master Boot Record (MBR) or GUID Partition Table (GPT) formats align (optional - default value '1MiB'; MBR only) Set the alignment of the partition. This must be a multiple of the block size (i.e. 512 bytes). The default of 1MiB (~ 2048 * 512 bytes blocks) is the default for modern systems and known to perform well on a wide range of targets. For each partition there might be some space that is not used - which is `align` - 512 bytes. For the default of 1MiB exactly 1048064 bytes (= 1 MiB - 512 byte) are not used in the partition itself. Please note that if a boot loader should be written to the disk or partition, there is a need for some space. E.g. grub needs 63 * 512 byte blocks between the MBR and the start of the partition data; this means when grub will be installed, the `align` must be set at least to 64 * 512 byte = 32 KiB. partitions (mandatory) A list of dictionaries. Each dictionary describes one partition. The following key / value pairs can be given for each partition: name (mandatory) The name of the partition. With the help of this name, the partition can later be referenced, e.g. when creating a file system. flags (optional) List of flags for the partition. Default: empty. Possible values: boot (MBR only) Sets the boot flag for the partition primary (MBR only) Partition should be a primary partition. If not set a logical partition will be created. size (mandatory) The size of the partition. The size can either be an absolute number using units like `10GiB` or `1.75TB` or relative (percentage) numbers: in the later case the size is calculated based on the remaining free space. type (optional) The partition type stored in the MBR or GPT partition table entry. For MBR the default value is '0x83' (Linux Default partition). Any valid one byte hexadecimal value may be specified here. For GPT the default value is '8300' (Linux Default partition). Any valid two byte hexadecimal value may be specified here. Due to ``sgdisk`` leading '0x' should not be used. Example: .. code-block:: yaml - partitioning: base: image0 label: mbr partitions: - name: part-01 flags: [ boot ] size: 1GiB - name: part-02 size: 100% - partitioning: base: data_image label: mbr partitions: - name: data0 size: 33% - name: data1 size: 50% - name: data2 size: 100% - partitioning: base: gpt_image label: gpt partitions: - name: ESP type: EF00 size: 16MiB - name: data1 size: 1GiB - name: lvmdata type: 8E00 size: 100% On the `image0` two partitions are created. The size of the first is 1GiB, the second uses the remaining free space. On the `data_image` three partitions are created: all are about 1/3 of the disk size. On the `gpt_image` three partitions are created: 16MiB one for EFI bootloader, 1GiB Linux filesystem one and rest of disk will be used for LVM partition. Module: LVM ........... This module generates volumes on existing block devices. This means that it is possible to take any previous created partition, and create volumes information in it. The symbolic name for this module is `lvm`. There are the following key / value pairs to define one set of volumes: pvs (mandatory) A list of dictionaries. Each dictionary describes one physical volume. vgs (mandatory) A list of dictionaries. Each dictionary describes one volume group. lvs (mandatory) A list of dictionaries. Each dictionary describes one logical volume. The following key / value pairs can be given for each `pvs`: name (mandatory) The name of the physical volume. With the help of this name, the physical volume can later be referenced, e.g. when creating a volume group. base (mandatory) The name of the partition where the physical volume needs to be created. options (optional) List of options for the physical volume. It can contain any option supported by the `pvcreate` command. The following key / value pairs can be given for each `vgs`: name (mandatory) The name of the volume group. With the help of this name, the volume group can later be referenced, e.g. when creating a logical volume. base (mandatory) The name(s) of the physical volumes where the volume groups needs to be created. As a volume group can be created on one or more physical volumes, this needs to be a list. options (optional) List of options for the volume group. It can contain any option supported by the `vgcreate` command. The following key / value pairs can be given for each `lvs`: name (mandatory) The name of the logical volume. With the help of this name, the logical volume can later be referenced, e.g. when creating a filesystem. base (mandatory) The name of the volume group where the logical volume needs to be created. size (optional) The exact size of the volume to be created. It accepts the same syntax as the -L flag of the `lvcreate` command. extents (optional) The relative size in extents of the volume to be created. It accepts the same syntax as the -l flag of the `lvcreate` command. Either size or extents need to be passed on the volume creation. options (optional) List of options for the logical volume. It can contain any option supported by the `lvcreate` command. Example: .. code-block:: yaml - lvm: name: lvm pvs: - name: pv options: ["--force"] device: root vgs: - name: vg base: ["pv"] options: ["--force"] lvs: - name: lv_root base: vg size: 1800M - name: lv_tmp base: vg size: 100M - name: lv_var base: vg size: 500M - name: lv_log base: vg size: 100M - name: lv_audit base: vg size: 100M - name: lv_home base: vg size: 200M On the `root` partition a physical volume is created. On that physical volume, a volume group is created. On top of this volume group, six logical volumes are created. Please note that in order to build images that are bootable using volumes, your ramdisk image will need to have that support. If the image you are using does not have it, you can add the needed modules and regenerate it, by including the `dracut-regenerate` element when building it. Level 2 +++++++ Module: Mkfs ............ This module creates file systems on the block device given as `base`. The following key / value pairs can be given: base (mandatory) The name of the block device where the filesystem will be created on. name (mandatory) The name of the partition. This can be used to reference (e.g. mounting) the filesystem. type (mandatory) The type of the filesystem, like `ext4` or `xfs`. label (optional - defaults to the name) The label of the filesystem. This can be used e.g. by grub or in the fstab. opts (optional - defaults to empty list) Options that will passed to the mkfs command. uuid (optional - no default / not used if not givem) The UUID of the filesystem. Not all file systems might support this. Currently there is support for `ext2`, `ext3`, `ext4` and `xfs`. Example: .. code-block:: yaml - mkfs: name: mkfs_root base: root type: ext4 label: cloudimage-root uuid: b733f302-0336-49c0-85f2-38ca109e8bdb opts: "-i 16384" Level 3 +++++++ Module: Mount ............. This module mounts a filesystem. The options are: base (mandatory) The name of the filesystem that will be mounted. name (mandatory) The name of the mount point. This can be used for reference the mount (e.g. creating the fstab). mount_point (mandatory) The mount point of the filesystem. There is no need to list the mount points in the correct order: an algorithm will automatically detect the mount order. Example: .. code-block:: yaml - mount: name: root_mnt base: mkfs_root mount_point: / Level 4 +++++++ Module: fstab ............. This module creates fstab entries. The following options exists. For details please consult the fstab man page. base (mandatory) The name of the mount point that will be written to fstab. name (mandatory) The name of the fstab entry. This can be used later on as reference - and is currently unused. options (optional, defaults to `default`) Special mount options can be given. This is used as the fourth field in the fstab entry. dump-freq (optional, defaults to 0 - don't dump) This is passed to dump to determine which filesystem should be dumped. This is used as the fifth field in the fstab entry. fsck-passno (optional, defaults to 2) Determines the order to run fsck. Please note that this should be set to 1 for the root file system. This is used as the sixth field in the fstab entry. Example: .. code-block:: yaml - fstab: name: var_log_fstab base: var_log_mnt options: nodev,nosuid dump-freq: 2 Legacy global filesystem configuration -------------------------------------- The ``disk-image-create`` tool has a number of historic global disk-related command-line options which are maintained for backwards compatibility. These options are merged as necessary by the block-device layer into the active configuration. If you are using more complicated block-device layouts with multiple partitions, you may need to take into account the special behaviour described below. The ``local_loop`` module will take it's default size from the following arguments: ``--image-size`` The size of loopback device which the image will be generated in, in gigabytes. If this is left unset, the size will be calculated from the on-disk size of the image and then scaled up by a fixed 60% factor. Can also set ``DIB_IMAGE_SIZE``. ``--image-extra-size`` Extra space to add when automatically calculating image size, in megabytes. This overrides the default 60% scale up as described above for ``--image-size``. Can also set ``DIB_IMAGE_EXTRA_SIZE``. The special node named ``mkfs_root`` is affected by the following; this reflects that the standard layout has only a single root partition so the options are, in effect, global for the default configuration. Note that if you are using multiple partitions, settings such as ``--mkfs-options`` will *not* apply to other partitions. The file-system type for the ``mkfs_root`` node is set by the ``FS_TYPE`` environment variable, and defaults to ``ext4``. ``xfs`` should also work. There is no command-line argument for this. The following options also affect the ``mkfs_root`` node configuration: ``--mkfs-options`` Options passed to mkfs when making the root partition. For ``ext4`` partitions, this by default sets a 4k byte-to-inode ratio (see below) and a default journal size of 64MiB. Note ``--mkfs-options`` are options passed to the mfks *driver* (i.e. ``mkfs.ext4``) rather than ``mkfs`` itself (i.e. arguments come after the initial ``mkfs -t `` argument). You also need to be careful with quoting. Can also set ``MKFS_OPTS``. By default, ``disk-image-create`` uses a 4k byte-to-inode ratio when creating the filesystem in the image. This allows large 'whole-system' images to utilize several TB disks without exhausting inodes. In contrast, when creating images intended for tenant instances, this ratio consumes more disk space than an end-user would expect (e.g. a 50GB root disk has 47GB available). If the image is intended to run within a tens to hundrededs of gigabyte disk, setting the byte-to-inode ratio to the ext4 default of 16k will allow for more usable space on the instance. The default can be overridden by passing ``'-i 16384'`` as a ``--mkfs-options`` argument. ``--mkfs-journal-size`` Only valid for ``FS_TYPE==ext4``. This value set the filesystem journal size in MB; overriding the default of 64MiB. Note the image size will be grown to fit the journal, unless ``DIB_IMAGE_SIZE`` is explicitly set. Can also set ``DIB_JOURNAL_SIZE``. ``--max-online-resize`` Only valid for ``FS_TYPE==ext4``; this value sets the maximum filesystem blocks when resizing. Can also set ``MAX_ONLINE_RESIZE``. ``--root-label`` The file-system label specified when creating the root file system. Defaults to ``cloudimg-rootfs`` for ``ext4`` and ``img-rootfs`` for ``xfs``. Can also set ``ROOT_LABEL``. Speedups -------- If you have 4GB of available physical RAM (as reported by /proc/meminfo MemTotal), or more, diskimage-builder will create a tmpfs mount to build the image in. This will improve image build time by building it in RAM. By default, the tmpfs file system uses 50% of the available RAM. Therefore, the RAM should be at least the double of the minimum tmpfs size required. For larger images, when no sufficient amount of RAM is available, tmpfs can be disabled completely by passing --no-tmpfs to disk-image-create. ramdisk-image-create builds a regular image and then within that image creates ramdisk. If tmpfs is not used, you will need enough room in /tmp to store two uncompressed cloud images. If tmpfs is used, you would still need /tmp space for one uncompressed cloud image and about 20% of that image for working files. Nameservers ----------- To ensure elements can access the network, ``disk-image-create`` replaces the ``/etc/resolv.conf`` within the chroot with a copy of the host's file early in the image creation process. The final ``/etc/resolv.conf`` can be controlled in a number of ways. If, during the build, the ``/etc/resolv.conf`` file within the chroot is replaced with a symlink, this will be retained in the final image [1]_. If the file is marked immutable, it will also not be touched. .. [1] This somewhat odd case was added for installation of the ``resolvconf`` package, which replaces ``/etc/resolv.conf`` with a symlink to it's version. Depending on its contents, and what comes after the installation in the build, this mostly works. If you would like specific contents within the final ``/etc/resolv.conf`` you can place them into ``/etc/resolv.conf.ORIG`` during the build. As one of the final steps, this file will be ``mv`` to ``/etc/resolv.conf``. Chosing an Architecture ----------------------- If needed you can specify an override the architecture selection by passing a ``-a`` argument like: :: disk-image-create -a ... Notes about PowerPC Architectures +++++++++++++++++++++++++++++++++ PowerPC can operate in either Big or Little Endian mode. ``ppc64`` always refers to Big Endian operation. When running in little endian mode it can be referred to as ``ppc64le`` or ``ppc64el``. Typically ``ppc64el`` refers to a ``.deb`` based distribution architecture, and ``ppc64le`` refers to a ``.rpm`` based distribution. Regardless of the distribution the kernel architecture is always ``ppc64le``. Notes about s390x (z Systems) Architecture ++++++++++++++++++++++++++++++++++++++++++ Images for s390x can only be build on s390x hosts. Trying to build it with the architecture override on other architecture will cause the build to fail.