/usr/bin/abootimg-pack-initrd is in abootimg 0.6-1.
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  | #!/bin/sh
#
if [ "$1" = "-f" ]; then
    forcewrite=yes
    shift
fi
initrd=${1:-initrd.img}
ramdisk=${2:-ramdisk}
if [ ! -d $ramdisk ]; then
    echo "$ramdisk does not exist."
    exit 1
fi
if [ -f $initrd -a -z "$forcewrite" ]; then
    echo "$initrd already exist."
    exit 1
fi
( cd $ramdisk; find | sort | cpio --quiet -o -H newc ) | gzip > $initrd
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