How to write "Magic Number" boot block to the first sector of my flash drive

Question

I want to try and see how the BIOS detects boot device using the magic number (0xaa55) by writing

e9 fd ff 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
*
00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa

to the first sector of my pendrive as said in the experiment in the book "Writing a Simple Operating System — from Scratch" (pg-4).

Can this be achieved by using dd command alone? I am using Ubuntu 20.04 LTS

Answer 1

I would use printf to produce the raw bytes and redirect it to dd for writing to the device.

You need to know the device name of your pendrive, but if it were /dev/sdf for example you could accomplish this in 3 steps.

Make sure you use the correct device name for your pendrive!

1. Zero out the first 512 byte sector:

printf '\x00%.0s' {1..512} | sudo dd of=/dev/sdf

2. Write the first 3 bytes to the start of the sector:

printf '\xe9\xfd\xff' | sudo dd of=/dev/sdf

3. Write the last 2 bytes to the end of the sector:

printf '\x55\xaa' | sudo dd seek=510 oflag=seek_bytes of=/dev/sdf