I have a CentOS LiveUSB and I was trying to modify the init script there. I extrated the initrd0.img file and I was able to find an init file in the syslinux directory. I added a line
shred -u -n 1 /dev/sdb
at the very first line of it. Yet when I repackage the initrd0.img and try to boot through the live usb, there is nothing changed to the disk (ie the init script should execute the shred commmand). The disk (/dev/sdb) has two partitions and there is a RHEL OS installed. After the shred command when the system is rebooted, the RHEL OS boots without any issue. Hence the shred command is not working at all.
If I run the shred command from with the live usb, the disks are wiped as expected. Hence I think the problem might be with the init script. Now how can I find the correct init script and effectively run the shred command from live USB?
Note: after the live usb boots the file at /etc/init does not look anything similar to the one in the initrd.