master_image.txt

# Find out size of all partitions
sudo fdisk -l /dev/sdb

# Each sector will most likely be 512 bytes.

# Backup master image of 2,435,841,536 bytes.
# count size is calculated this way: 2,435,841,536 / 1024 / 1024
# Round count size up to the nearest integer.
sudo dd bs=1M count=2323 if=/dev/sdb of=build-lights-master-20161028.img

# Compress the image
zip build-lights-master-20161028.zip build-lights-master-20161028.img

# Copy master image to another SD card
sudo dd bs=1M if=build-lights-master-20161028.img of=/dev/sdb