diskimage-builder/diskimage_builder/elements/partitioning-sfdisk/environment.d/10-partitioning-sfdisk

DEFAULT_SCHEMA="2048 + L *
             0 0;
             0 0;
             0 0;"
export DIB_PARTITIONING_SFDISK_SCHEMA=${DIB_PARTITIONING_SFDISK_SCHEMA:-$DEFAULT_SCHEMA}