Docker image disk usage tool

imagesize.sh

#!/bin/env sh

# imagesize.sh calculates the on disk size of images by pulling
# and comparing inode and block usage. Requires using a fresh
# device to accurately measure the difference caused by each
# image. This is intended to measure the on disk size caused
# by pulling an image with docker rather than the sum of all
# the file usage just inside the docker graph driver directory.
#
# Usage:
#   sh imagesize.sh <device> <storage driver> [<image>, ...]
#
# How to use:
#   $ fallocate -l 18GB testvolume
#   $ device=$(sudo losetup -f --show ./testvolume)
#   $ sudo mkfs.ext4 -F $device
#   $ sudo sh imagesize.sh $device overlay ubuntu:latest golang:latest


tmpdir=$(mktemp -d)
device=$1
graphdriver=$2
shift
shift

mount $device $tmpdir
echo "Mounted $device to $tmpdir"

echo "Starting docker engine using $graphdriver storage driver"
docker daemon -D -s $graphdriver -g $tmpdir > /tmp/dockertestlog.txt 2>&1 &

sleep 10

base=$(df --output=used $tmpdir | tail -n 1)
basei=$(df --output=iused $tmpdir | tail -n 1)

function usage_diff() {
	usage=$(df --output=used $tmpdir | tail -n 1)
	usagei=$(df --output=iused $tmpdir | tail -n 1)

	diff=$(expr $usage - $base)
	diffi=$(expr $usagei - $basei)
	base=$usage
	basei=$usagei

	echo "Size($1):   $diff"
	echo "Inodes($1): $diffi"
}

for image in "$@"; do
	echo "Pulling $image"
	docker pull $image

	usage_diff $image
done

kill $(cat /var/run/docker.pid)

sleep 2

umount $tmpdir

rmdir $tmpdir

echo "Unmounted and remove $tmpdir"