Bash Script for Shrinking/Truncating a disk image

rock64shrink.sh

#!/bin/bash

# WARNING this script could easily trash a image or worse a device. DO NOT USE IT WITH A DEVICE
# It will make a copy of the image to work on by default unless you use the -o option 
# which you should NOT unless your image is much bigger than >16GB
# In other words test it on a disk image file that could be damaged.

# Use the -h option to see list of options

# You MUST use -t to do the last step truncation 

# Will ONLY shink the LAST partition which needs to be the root partition of a disk image (likely from and SD or EMMC)
# Should work for any image with above although for for Ayufan rock64 bionic images this will reset the auto expander on first boot.

version="v0.0.1"

function info() {
	echo "$SCRIPTNAME: $1..."
}

function error() {
	echo -n "$SCRIPTNAME: ERROR occured in line $1: "
	shift
	echo "$@"
}

function cleanup() {
	if losetup "$loopback" &>/dev/null; then
		losetup -d "$loopback"
	fi
	if [ "$log" = true ]; then
		local old_owner=$(stat -c %u:%g "$src")
		chown "$old_owner" "$LOGFILE"
	fi

}

function logVariables() {
	if [ "$log" = true ]; then
		if [ "$verbose" = true ]; then echo "========= Log AT Line $1 ==========" >> "$LOGFILE";fi
		shift
		local v var
		for var in "$@"; do
			eval "v=\$$var"
			echo "$var: $v" >> "$LOGFILE"
		done
		if [ "$verbose" = true ]; then echo "------------------------------------" >> "$LOGFILE";fi
	fi
}

function logVerbose() {
	if [ "$verbose" = true ]; then
	logVariables "$@"
	fi
}

function checkFilesystem() {
	info "Checking filesystem"
	e2fsck -pf "$loopback"
	(( $? < 4 )) && return

	info "Filesystem error detected!"

	info "Trying to recover corrupted filesystem"
	e2fsck -y "$loopback"
	(( $? < 4 )) && return

if [[ $repair == true ]]; then
	info "Trying to recover corrupted filesystem - Phase 2"
	e2fsck -fy -b 32768 "$loopback"
	(( $? < 4 )) && return
fi
	error $LINENO "Filesystem recoveries failed. Giving up..."
	exit -9

}

help() {
	local help
	read -r -d '' help << EOM
Usage: $0 [-osdlvtrzh] imagefile.img [newimagefile.img]

	-o: Overwrite input image"
  -s: Don't expand filesystem when image is booted the first time
  -d: Dry Run don't actually shrink
	-l: Write debug messages in a debug log file
	-v: Include extra information in debug log files
	-t: truncate the image file of unpartioned space
	-r: Use advanced filesystem repair option if the normal one fails
  -z: Gzip compress image after shrinking
EOM
	echo "$help"
	exit -1
}

usage() {
	echo "Usage: $0 [-osldvtrzho] imagefile.img [newimagefile.img]"
	echo ""
	echo "  -o: Overwrite input image"
	echo "  -s: Skip autoexpand"
	echo "  -l: logging"
	echo "  -d: dry run"
	echo "  -v: verbose logging"
	echo "  -t: truncate image"
	echo "  -r: Use advanced repair options"
	echo "  -z: Gzip compress image"
	echo "  -h: display help text"
	exit -1
}

should_skip_autoexpand=false
log=false
overwrite=false
dryrun=false
verbose=false
repair=false
gzip_compress=false
truncate=false

while getopts ":osdltrzhv" opt; do
  case "${opt}" in
		o) overwrite=true ;;
    s) should_skip_autoexpand=true ;;
    l) log=true;;
		d) dryrun=true;;
		v) verbose=true;;
		t) truncate=true;;
    r) repair=true;;
    z) gzip_compress=true;;
    h) help;;
    *) usage ;;
  esac
done
shift $((OPTIND-1))


#Args
src="$1"
img="$1"
CURRENT_DIR=$(pwd)
SCRIPTNAME="${0##*/}"
FILENAME=$(basename $1 .img)
if [ "$overwrite" = false ]; then FILENAME=${2:-$(echo "$FILENAME-shrunk")}; fi
LOGFILE=${CURRENT_DIR}/${FILENAME}.log
echo $FILENAME $LOGNAME
if [ "$log" = true ]; then
	info "Creating log file $LOGFILE"
	rm "$LOGFILE" &>/dev/null
	exec 1> >(stdbuf -i0 -o0 -e0 tee -a "$LOGFILE" >&1)
	exec 2> >(stdbuf -i0 -o0 -e0 tee -a "$LOGFILE" >&2)
fi

echo "${0##*/} $version"

#Usage checks
if [[ -z "$img" ]]; then
  usage
fi
if [[ ! -f "$img" ]]; then
  error $LINENO "$img is not a file..."
  exit -2
fi
if (( EUID != 0 )); then
  error $LINENO "You need to be running as root."
  exit -3
fi

#Check that what we need is installed
for command in parted losetup truncate bc tune2fs e2fsck resize2fs sgdisk; do
  command -v $command >/dev/null 2>&1
  if (( $? != 0 )); then
    error $LINENO "$command is not installed."
    exit -4
  fi
done

#Copy to new file unless not request
if [ "$overwrite" = false ]; then
	info "Copying $1 to $FILENAME.img"
  cp --reflink=auto --sparse=always "$1" "$FILENAME.img"
  if (( $? != 0 )); then
    error $LINENO "Could not copy file..."
    exit -5
  fi
  old_owner=$(stat -c %u:%g "$1")
  chown "$old_owner" "$2"
  img="$FILENAME.img"
fi

# cleanup at script exit
trap cleanup ERR EXIT

#Gather info
info "Gathering data"
diskinfo=$(fdisk -l $img)
bps=$(echo "$diskinfo" | grep Units | perl -pe 's/.*=//g;s/[^0-9]//g')
partname=$(echo "$diskinfo" | tail -n 1 | perl -pe 's/ +/\t/g' | cut -f 1)
partnum=${partname: -1}
pss=$(echo "$diskinfo" | tail -n 1 | perl -pe 's/ +/\t/g' | cut -f 2)
partstart=$(echo "$pss*$bps" | bc)
beforesize=$(ls -lh "$img" | cut -d ' ' -f 5)
loopback=$(losetup -f --show -o "$partstart" "$img")
tune2fs_output=$(tune2fs -l "$loopback")
currentsize=$(echo "$tune2fs_output" | grep '^Block count:' | tr -d ' ' | cut -d ':' -f 2)
blocksize=$(echo "$tune2fs_output" | grep '^Block size:' | tr -d ' ' | cut -d ':' -f 2)

logVerbose $LINENO diskinfo
logVariables $LINENO img parted_output partname partnum partstart
logVerbose $LINENO tune2fs_output currentsize blocksize
logVariables $LINENO currentsize blocksize

#Make sure filesystem is ok
checkFilesystem

if ! minsize=$(resize2fs -P "$loopback"); then
	rc=$?
	error $LINENO "resize2fs failed with rc $rc"
	exit -10
fi
minsize=$(cut -d ':' -f 2 <<< "$minsize" | tr -d ' ')
logVariables $LINENO minsize

#Add some free space to the end of the filesystem
extra_space=$(($currentsize - $minsize))
logVariables $LINENO extra_space
for space in 5000 1000 100; do
  if [[ $extra_space -gt $space ]]; then
    minsize=$(($minsize + $space))
    break
  fi
done
logVariables $LINENO minsize

if [ "$dryrun" = true ]; then
	info "Dry Run"
	echo See $LOGFILE
	exit -1
else

echo "============ Proceeding with Image Shrink ==========="

#Shrink filesystem

if [[ $currentsize -eq $minsize ]]; then
  echo "Image already shrunk to smallest size"
else
	info "Shrinking filesystem"
	resize2fs -M "$loopback" $minsize
	if [[ $? != 0 ]]; then
	  error $LINENO "resize2fs failed"
	  losetup -d "$loopback"
	  exit -12
	else
		#Check if we should expand rootfs on next boot
		if [ "$should_skip_autoexpand" = false ]; then
		  mountdir=$(mktemp -d)
		  mount "$loopback" "$mountdir"
			if [ $? -eq 0 ]; then
				name=$(cat "$mountdir/etc/hostname")
				info "setting image up to expand root partition at first boot"
			  echo "Mount of root partition hostname:${name} succeeded!"
				rm -f "$mountdir/var/lib/rock64/resized"
				if [ ! -e "$mountdir/var/lib/rock64/resized" ]; then
					info "removed /var/lib/rock64/resized, partition will resize at boot "
				else
					info "unable to remove /var/lib/rock64/resized, partition will NOT! resize at boot "
				fi
				umount "$mountdir"
			else
				echo "Crap! Mount Failed :(, Shrunk Partition is corrupt"
				exit -1
			fi
		else
		  info "Skipping autoexpanding process..."
		fi
	info "destroying the current loopback"
	losetup -d "$loopback"
	fi
	sleep 1

	#Shrink partition
	partnewsize=$(($minsize * $blocksize))
	newpartend=$(($partstart + $partnewsize))
	logVariables $LINENO partnewsize newpartend
	echo "Shrinking partition to minimal"
	if ! parted -s -a minimal "$img" rm "$partnum"; then
		rc=$?
		error $LINENO "parted failed with rc $rc"
		exit -13
	fi
	echo "resetting partition new size $partnewsize new end $newpartend"
	if ! parted -s "$img" unit B mkpart primary "$partstart" "$newpartend" name "$partnum" linuxfs-root; then
		rc=$?
		error $LINENO "parted failed with rc $rc"
		exit -14
	fi

	loopback=$(losetup -f --show -o "$partstart" "$img")
	checkFilesystem

  mountdir=$(mktemp -d)
	mount "$loopback" "$mountdir"
	if [ $? -eq 0 ]; then
	  name=$(cat "$mountdir/etc/hostname")
		echo "Mount of root partition hostname:${name} succeeded!"
		umount "$mountdir"
	else
	  echo "Crap! Mount Failed :(, Shrunk Partition is corrupt"
		exit -1
	fi

	echo "before partion shrink
	echo  $diskinfo" | tail -n 1
	newdiskinfo=$(fdisk -l $img)
	echo "after after shrink:
	echo $newdiskinfo" | tail -n 1
	info "now doing a filesystem and mount check of root partition"

fi  # end shrink

if [ "$truncate" = true ]; then
	info "Truncating Image of Unpartitioned Free Space"
	newdiskinfo=$(fdisk -l $img)
	endsector=$(echo "$newdiskinfo" | tail -n 1  | perl -pe 's/ +/\t/g' | cut -f 3)
	# add 33 for gpt backup
	newsize=$(echo "($endsector+1+33)*$bps" | bc)
	info "truncating $img to sector $endsector which will give size of $(printf %.2f $(echo "$newsize/10^9" | bc -l)) GB"
	echo "with command 'truncate --size=$newsize $img'"
	echo -n "enter 'y' to proceed >"
	read choice
	if [ "$choice" = "y" ]; then
		if ! truncate --size=$newsize $img; then
		rc=$?
		error $LINENO "error truncating image $rc"
		exit -14
	  fi
	if ! sgdisk -e "$img"  > /dev/null; then
	   rc=$?
	   error $LINENO "error moving backup gpt table to end of image $rc"
	   exit -14
	 fi
	 echo 'image truncation and gpt fix succeded'
	else
		echo "Image truncation aborted"
	fi
else
	echo "Image will not be truncated"
fi

if [[ $gzip_compress == true ]]; then
    info "Gzipping the shrunk image"
    if [[ ! $(gzip -f9 "$img") ]]; then
        img=$img.gz
    fi
fi

aftersize=$(ls -lh "$img" | cut -d ' ' -f 5)
logVariables $LINENO aftersize

info "Shrunk $img from $beforesize to $aftersize"

fi

Hi, came across your script and thought I would try it, but it fails each time with the same error:

# shrink -v PK191029A-UEFI.img
PK191029A-UEFI-shrunk root
shrink v0.0.1
shrink: Copying PK191029A-UEFI.img to PK191029A-UEFI-shrunk.img...
chown: cannot access '': No such file or directory
shrink: Gathering data...
shrink: Checking filesystem...
/dev/loop0: recovering journal
/dev/loop0: 103405/439776 files (0.1% non-contiguous), 706180/1757696 blocks
resize2fs 1.44.5 (15-Dec-2018)
============ Proceeding with Image Shrink ===========
shrink: Shrinking filesystem...
resize2fs 1.44.5 (15-Dec-2018)
Resizing the filesystem on /dev/loop0 to 792782 (4k) blocks.
The filesystem on /dev/loop0 is now 792782 (4k) blocks long.

shrink: setting image up to expand root partition at first boot...
Mount of root partition hostname:pure-1c1b0dfc2a43 succeeded!
shrink: removed /var/lib/rock64/resized, partition will resize at boot ...
shrink: destroying the current loopback...
Shrinking partition to minimal
resetting partition new size 3267715072 new end 3523567616
losetup: PK191029A-UEFI-shrunk.img: failed to set up loop device: Resource temporarily unavailable
shrink: Checking filesystem...
e2fsck: No such file or directory while trying to open
Possibly non-existent device?
shrink: Filesystem error detected!...
shrink: Trying to recover corrupted filesystem...
e2fsck 1.44.5 (15-Dec-2018)
e2fsck: No such file or directory while trying to open
Possibly non-existent device?
shrink: ERROR occured in line 73: Filesystem recoveries failed. Giving up...

I have tried several files, and all fail at the same point / error:

losetup: PK191029A-UEFI-shrunk.img: failed to set up loop device: Resource temporarily unavailable

I am running debian 10 as a vmware virtual machine.

Any idea what the cause may be ??