Changed sd card disk signature in diskpart, now gets stuck booting

Question

I have an SD card with a particular image on it that I wanted to back up before modifying anything in case I broke something. I inserted the card into my (Windows) PC and attempted to use Win32 Disk Imager, but the disk was offline because it had a signature collision, according to diskpart. Google said the solution was to change the unique ID of the disk in diskpart, which I did without writing down the original ID. It still wouldn't come online until I rebooted the PC (which I probably should have done first). Now my PC thinks the card is fine, but when I put it in the Pi and turn it on, it begins the boot sequence but won't progress any further after recognizing storage.

The last few lines of the boot sequence are:

[  1.325488] mmc1: new high speed SDIO card at address 0001
[  1.325968] mmc0: host does not support reading read-only switch, assuming write-enable
[  1.348842] mmc0: new high speed SDHC card at address 5048
[  1.347130] mmcblk0: mmc0:5048 SD8GB 7.47 GiB
[  1.354989]  mmcblk0: p1 p2

After that the cursor just stays blinking. Double space on the last line is not a typo.

Edit: after about 7 minutes another line shows:

[422.231548] random: crng init done

Is there a way to get the disk working again without wiping/reformatting etc? The whole point was trying to back it up because I don't have another copy of the image.

Answer 1

If you setup a Pi with SD reader you can use the following script to check consistency of a Raspbian/Raspberry Pi OS SD Card image in the reader.

#! /bin/bash
# 2021-02-10
# Check consistency of Partition ID on mounted SD Card

BOOT_MOUNT='/mnt/SDA1'
ROOT_MOUNT='/mnt/SDA2'

# Check/create Mount Points
if [ ! -e $BOOT_MOUNT ]; then
    mkdir $BOOT_MOUNT
fi
if [ ! -e $ROOT_MOUNT ]; then
    mkdir $ROOT_MOUNT
fi
    echo "mounts " $BOOT_MOUNT  $ROOT_MOUNT
if [ -e /dev/sda ]; then
    SD1='/dev/sda1'
    SD2='/dev/sda2'
    SD='/dev/sda'
else
    SD1='/dev/sdb1'
    SD2='/dev/sdb2'
    SD='/dev/sdb'
fi
echo $SD

# Mount Partitions
if ! $(mountpoint -q $BOOT_MOUNT); then
    sudo mount $SD1 $BOOT_MOUNT # mount partition containing boot files
fi
if ! $(mountpoint -q $ROOT_MOUNT); then
    sudo mount $SD2 $ROOT_MOUNT # mount root partition containing OS files
fi


# Determine Disk identifier of SD Card
DISKID=$(sudo fdisk -l $SD | awk '/Disk identifier/ {print $3};' | sed 's/0x//')

# Use sed to delete all BEFORE PARTUUID= and all AFTER -0  in $BOOT_MOUNT/cmdline.txt
ROOTPART=$(sed -e 's/^.*PARTUUID=//' -e 's/-0.*$'// $BOOT_MOUNT/cmdline.txt)

echo -e "Disk ID\t\t"$DISKID
echo -e "root PARTUUID\t"$ROOTPART

# find first PARTUUID ext4 in $ROOT_MOUNT/etc/fstab
EXISTFSTABPART=$(awk '/PARTUUID.*ext4/ {print $1; exit};' $ROOT_MOUNT/etc/fstab | sed -e 's/^.*PARTUUID=//' -e 's/-0.*$'//)

echo -e "Existing fstab\t"$EXISTFSTABPART

if [ $DISKID = $EXISTFSTABPART ]; then
    echo "Looks OK!"
else
    echo "Partition ID mismatch!"
    # Edit cmdline.txt & fstab to new DISKID & create new temporary files
    sed -e "s/$ROOTPART/$DISKID/" $BOOT_MOUNT/cmdline.txt > cmdline.txt.new
    sed -e "s/$ROOTPART/$DISKID/" $ROOT_MOUNT/etc/fstab > fstab.new
    echo -n "Set DiskID to ${DISKID} on $SD (y/n)? "
    while read -r -n 1 -s answer; do
        if [[ "${answer}" = [yY] ]]; then
          echo "Change"
          sudo cp -v cmdline.txt.new $BOOT_MOUNT/cmdline.txt
          sudo cp -v fstab.new $ROOT_MOUNT/etc/fstab
          break
        else
          echo "Aborted"
          exit
        fi
    done
fi