Once you create an image from an SD card, the resulting file is always the full capacity of the card, which may be way more than the actual data storage size. Copy the script below and paste it in a new file…suppose it’s called script.sh…which can then be executed as follows to shrink the image file to a more manageable size:
sudo bash ./script.sh pi.img
The script:
#!/bin/env bash
IMG="$1"
if [[ -e $IMG ]]; then
P_START=$( fdisk -lu $IMG | grep Linux | awk '{print $2}' ) # Start of 2nd partition in 512 byte sectors
P_SIZE=$(( $( fdisk -lu $IMG | grep Linux | awk '{print $4}' ) * 512 )) # Partition size in bytes
losetup /dev/loop2 $IMG -o $(($P_START * 512)) --sizelimit $P_SIZE
fsck -f /dev/loop2
resize2fs -M /dev/loop2 # Make the filesystem as small as possible
fsck -f /dev/loop2
P_NEWSIZE=$( dumpe2fs /dev/loop2 2>/dev/null | grep '^Block count:' | awk '{print $3}' ) # In 4k blocks
P_NEWEND=$(( $P_START + ($P_NEWSIZE * 8) - 1 )) # in 512 byte sectors
losetup -d /dev/loop2
echo -e "p\nd\n2\nn\np\n2\n$P_START\n$P_NEWEND\np\nw\n" | fdisk $IMG
I_SIZE=$((($P_NEWEND + 1) * 512)) # New image size in bytes
truncate -s $I_SIZE $IMG
else
echo "Usage: $0 filename"
fi
After writing this image to a card and booting from it, the filesystem can be re-expanded to the full card using:
sudo raspi-config --expand-rootfs
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