dd tool  (data duplicator)

Linux DD Command - 15 Examples with All Options
( https://linoxide.com/linux-dd-command-create-1gb-file/ )

1. Backing up and restoring an entire disk or a partition
a. Backup entire disk to disk
# dd if=/dev/sda of=/dev/sdb bs=4096 conv=noerror,sync

b. Creating dd disk image (file image)
# dd if=/dev/sda of=/tmp/sdadisk.img

c. Creating a compressed disk image
# dd if=/dev/vda | gzip -c >/tmp/vdadisk.img.gz
The -c option writes output on standard output and keeps original files unchanged.

d. Backup a partition or clone one partition to another
# dd if=/dev/sda1 of=/dev/sdb1 bs=4096 conv=noerror,sync

2. Creating virtual filesystem/Backup images of CD or DVDs as iso files

a. Creating a virtual filesystem
# dd if=/dev/zero of=/file bs=1024K count=500

b. Modify the first 512 bytes of a file with null data
If during the operation you indicate an existing output file, you will lose its data. For some reasons, you can need to replace a block size of the output file.

dd if=/dev/zero of=file1 bs=512 count=1 conv=notrunc

The notrunc option refers to do not truncate the file, only replace the first 512 bytes, if it exists. Otherwise, you will get a 512 byte file

c. Creating a backup iso image of CD or DVD

# dd if=/dev/cdrom of=/mycd.iso

# mount -o loop /mycd.iso /mnt/cd

d) Create a bootable USB Drive

# dd if=~/Downloads/CentOS-8-x86_64-1905-dvd1.iso of=/dev/sdb bs=1M

3. Backing up and restoring MBR

a. Backing up MBR
Because the MBR makes up the first 512 bytes of the disk, we just need to copy that block size

# dd if=/dev/sda of=/tmp/sdambr.img bs=512 count=1

With the count=1 and bs=512, only 512 bytes will be copied which correspond to the size of our MBR.
You can display the saved MBR with the od command which dump files in octal and other formats as below

# od -xa /tmp/sdambr.img
0000000    bf52    81f4    8b66    832d    087d    0f00    e284    8000
          R   ?   t soh   f  vt   - etx   }  bs nul  si eot   b nul nul
0000020    ff7c    7400    6646    1d8b    8b66    044d    3166    b0c0
          | del nul   t   F   f  vt  gs   f  vt   M eot   f   1   @   0

-a option  selects named characters and -x selects hexadecimal 2-byte units

b. Backing up the boot data of MBR excluding the partition table

# dd if=/dev/sda of=/tmp/sdambr2.img bs=446 count=1

c. Restoring MBR from MBR image
You can restore your MBR as shown on the previous commands with

# dd if=/tmp/sdambr.img of=/dev/sda


3. Converting data formats

If an input file uses a character set that is not the native character set of the host computer, the import operator must perform a conversion. For example, if ASCII is the native format for strings on your host computer, but the input data file represents strings using EBCDIC, you must convert EBCDIC to ASCII and vice versa.
a. Convert the data format of a file from EBCDIC to ASCII

3. Converting data formats
If an input file uses a character set that is not the native character set of the host computer, the import operator must perform a conversion. For example, if ASCII is the native format for strings on your host computer, but the input data file represents strings using EBCDIC, you must convert EBCDIC to ASCII and vice versa.

a. Convert the data format of a file from EBCDIC to ASCII
If there’s an ebcdic file with you, mostly retrieved from mainframe systems, then, you would like to convert them to ASCII for making modifications using text editors on UNIX servers

# dd if=textfile.ebcdic of=textfile.ascii conv=ascii