/bin/autopartition is in ubiquity 18.04.14.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45  | #!/bin/sh
. /lib/partman/lib/base.sh
. /lib/partman/lib/recipes.sh
. /lib/partman/lib/auto-shared.sh
devs="$1"
clean_method
for dev in $devs; do
	cd $dev
	[ -f size ] || exit 1
	size=$(cat size)
	target="$(humandev $(cat device)) - $(cat model)"
	if [ -z "$2" ]; then
		# Only one parameter. Being run for initial autopartitioning.
		target="$target: $(longint2human $size)"
		free_size=$(convert_to_megabytes $size)
		choose_recipe default "$target" "$free_size" || exit $?
		auto_init_disks "$dev" || exit $?
		get_last_free_partition_infos $dev
	else
		# Two parameters, being run on selected free space.
		free_space=$2
		open_dialog PARTITION_INFO $free_space
		read_line x1 x2 free_size x3 x4 x5 x6
		close_dialog
		target="$target: $(longint2human $free_size) ($(longint2human $size))"
		free_size=$(convert_to_megabytes $free_size)
		choose_recipe default "$target" "$free_size" || exit $?
	fi
	perform_recipe $dev $free_space $recipe || exit $?
done
# default to accepting the autopartitioning
menudir_default_choice /lib/partman/choose_partition finish finish || true
 |