RPI .img or .dmg unrecognized

Question

I have made several images/clones of my SD disk from my Raspberry Pi. I have used the dd method via the Mac terminal, I've used the disk utility via the desktop. I found directions from other postings. I've copied the syntax correctly and the creating of the image shows bytes transferred and completes without failures. All looks good. Then when I go to restore the clone to a newly reformatted SD disk (using the SDformatter app.) then either via terminal or the Mac disk utility I try to restore the image I run into problems. From Mac disk utility I get an error "Could not validate source - Invalid argument". Using the terminal (sudo dd if=~/Desktop/raspberrypi.dmg of=/dev/disk2) verified the location of the sd disk by diskutil list. It takes about 3.4 hrs to copy over (32GB SD). When I unmount the disk, then put it back in the card reader I get the message ~ Cannot verify or recognize the format...

What would cause the image to be unusable for restore?

Answer 1

First - unless you you use raw disk mode backup and restore will be glacially slow. I doubt the copy or restore would complete in 3.4hrs, so you probably had an incomplete image. The following are the scripts I use on my Mac. (And before @goldilocks adds his comment, I usually use rsync to make copies.)

#!/bin/bash
# script to backup Pi SD card
# 2017-02-10
# DSK='disk4'   # manual set disk
OUTDIR=~/temp/Pi
# Find disk with Linux partition (works for Raspbian)
# Modified for PINN/NOOBS
export DSK=`diskutil list | grep "Linux" | sed 's/.*\(disk[0-9]\).*/\1/' | uniq`
if [ $DSK ]; then
    echo $DSK
    echo $OUTDIR
else
    echo "Disk not found"
    exit
fi

diskutil unmountDisk /dev/$DSK
echo please wait - This takes some time
echo Ctl+T to show progress!    
time sudo dd if=/dev/r$DSK bs=4m | gzip -9 > $OUTDIR/Piback.img.gz
#rename to current date
echo compressing completed - now renaming
mv -n $OUTDIR/Piback.img.gz $OUTDIR/Piback`date +%Y%m%d`.img.gz

And this is the script I use to restore:-

NOTE These days I just use Etcher which is easier (and safer)

#!/bin/bash
# script to restore backup to Pi SD card
# 2017-05-26

DSK='disk4'

# Image name (no ext)
IMG='2017-04-10-raspbian-jessie-lite'

# Check for sensible disk
export PTYPE=$(diskutil list  /dev/$DSK | awk '/GUID_partition_scheme/ {print $2}; /Apple/ {print $2}; /Windows_NTFS/ {print $2}' )
if [ "$PTYPE" ]; then
    echo "Disk not a SD Card - Contains "$PTYPE
    exit
elif [ ! /dev/$DSK ]; then
    echo "/dev/$DSK not found"
    exit
fi

echo Ensure SD partitions are unmounted!
diskutil unmountDisk /dev/$DSK

# Check if image exists - else try to uncompress
if [ -s $IMG.img ]; then
echo $IMG.img exists
elif [ -s $IMG.img.gz ]; then
echo Uncompressing $IMG.img.gz
echo Ctl+T to show progress!
time  gunzip -k $IMG.img.gz
fi

echo please wait - This takes some time
echo Ctl+T to show progress!
time sudo dd if=$IMG.img of=/dev/r$DSK bs=1m

exit