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ubuntu
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Use Ubuntu cloud images as the baseline for built disk images.
Overrides:
* To use a non-default URL for downloading base Ubuntu cloud images,
use the environment variable DIB\_CLOUD\_IMAGES
* To download a non-default release of Ubuntu cloud images, use the
environment variable DIB\_RELEASE. This element will export the DIB_RELEASE
variable.
* To use different mirrors rather than the default of archive.ubuntu.com and
security.ubuntu.com, use the environment variable DIB\_DISTRIBUTION\_MIRROR
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