Custom Disk Partitions

KIWI NG has its own partitioning schema which is defined according to several different user configurations: boot firmware, boot partition, expandable layouts, etc. Those supported features have an impact on the partitioning schema.

MBR or GUID partition tables are not flexible, carry limitations and are tied to some specific disk geometry. Because of that the preferred alternative to disk layouts based on traditional partition tables is using flexible approaches like logic volumes.

However, on certain conditions additional entries to the low level partition table are needed. For this purpose the <partitions> section exists and allows to add custom entries like shown in the following example:

<partitions>
    <partition name="var" size="100" mountpoint="/var" filesystem="ext3"/>
</partitions>

Each <partition> entry puts a partition of the configured size in the low level partition table, creates a filesystem on it and includes it to the system’s fstab file. If parts of the root filesystem are moved into its own partition like it’s the case in the above example, this partition will also contain the data that gets installed during the image creation process to that area.

The following attributes must/can be set to configured a partition entry:

name=”identifier”

Mandatory name of the partition as handled by KIWI NG.

Note

There are the following reserved names which cannot be used because they are already represented by existing attributes: root, readonly, boot, prep, spare, swap, efi_csm and efi.

partition_name=”name”

Optional name of the partition as it appears when listing the table contents with tools like gdisk. If no name is set KIWI NG constructs a name of the form p.lx(identifier_from_name_attr)

partition_type=”type_identifier”

Optional partition type identifier as handled by KIWI NG. Allowed values are t.linux and t.raid. If not specified t.linux is the default.

size=”size_string”

Mandatory size of the partition. A size string can end with M or G to indicate a mega-Byte or giga-Byte value. Without a unit specification mega-Byte is used.

mountpoint=”path”

Mandatory mountpoint to mount the partition in the system.

filesystem=”btrfs|ext2|ext3|ext4|squashfs|xfs

Mandatory filesystem configuration to create one of the supported filesystems on the partition.

clone=”number”

Optional setting to indicate that this partition should be cloned number of times. A clone partition is content wise an exact byte for byte copy of the origin. However, to avoid conflicts at boot time the UUID of any cloned partition will be made unique. In the sequence of partitions, the clone(s) will always be created first followed by the partition considered the origin. The origin partition is the one that will be referenced and used by the system

Despite the customization options of the partition table shown above there are the following limitations:

  1. The root partition is always the last one

    Disk imags build with KIWI NG are designed to be expandable. For this feature to work the partition containing the system rootfs must always be the last one. If this is unwanted for some reason KIWI NG offers an opportunity for one extra/spare partition with the option to be also placed at the end of the table. For details lookup spare_part in Image Description Elements

  2. There can be no gaps in the partition table

    The way partitions are configured does not allow for gaps in the table. As of today there was no use case were it made sense to leave a gap between table entries. However, leaving some space free at the end of the partition geometry is possible in the following ways:

    • Deploy with unpartitioned free space.

      To leave space unpartitioned on first boot of a disk image it is possible to configured an <oem-systemsize> which is smaller than the disk the image gets deployed to. Details about this setting can be found in Image Description Elements

    • Build with unpartitioned free space.

      Setting some unpartitioned free space on the disk can be done using the unpartitioned attribute of size element in type’s section. For details see Modifying the Size of the Image

    • Resize built image adding unpartitioned free space.

      A built image can be resized by using the kiwi-ng image resize command and set a new extended size for the disk. See KIWI NG commands docs here.