To use iReb effectively, follow these general steps:

ddrescue -R -n --min-read-rate=1M -O 41-500,421-900 /dev/sr0 disk.img disk.log

: This typically refers to a tool (originally by developer iH8sn0w) used for putting iOS devices into a "Pwned DFU" state to allow the installation of custom firmware. 40x / 41 / 421

Given that this software is over a decade old and primarily used for devices running iOS 4.0 through 4.2.1