dd tricks

dd-tricks-copy-only-allocated-space.sh

#!/bin/bash

sudo fdisk -lu /dev/sdb

# Disk /dev/sdb: 14.9Gib, 1593153946 bytes, 31116288 sectors
# Units: sectors of 1 * 512 = 512 bytes
# Secor size (logical/physical): 512 bytes / 512 bytes
# I/O size (minimum/optimal): 512 bytes / 512 bytes
# Disklabel type: dos
# Disk identifier: 0x9c4e41cd
#
# Device    Boot Start    End Sectors Size Id Type
# /dev/sdb1 *     2048 133119  131072  64M  c W95 FAT32 (LBA)

## find the END sector number for the last partition, in this case, 133119
## add 1 for the zero-indexed sector, so 133120
## and match the sector size

sudo dd if=/dev/sdb of=./smaller-image.img bs=512 count=133120

## and on restore, use the same
sudo dd if=./smaller-image.img of=/dev/sdb bs=512

dd-tricks-skip-zeroes.sh

#!/bin/bash

## mount the partition so it can be zero-filled
mkdir ~/srcfs && mound /dev/sdXN ~/srcfs
## fill the partition with zeroes
dd if=/dev/zero of=~/srcfs/tempzero.txt
## delete the file
rm ~/srcfs/tempzero.txt
## tell dd to "punch" zeroes from the image when reading
dd conv=sparse if=/dev/sdXN of=./image.img
## punch zeroes when writing back out
dd conv=sparse if=./image.img of=/dev/sdXN

dd-tricks.bashrc

alias ddstatus='sudo kill -USR1 $(pgrep ^dd)'
alias ddwatch='watch -n5 "sudo kill -USR1 $(pgrep ^dd)"'

See also https://gist.github.com/AndreiCherniaev/12e360601b1bfe15cdb1e79ce3a8e31e