dd

Additional Notes

dd copies raw bytes from an input to an output. It is commonly used for disk images, USB writing, device reads, zero-filling, and low-level data conversion.

It is powerful and dangerous because a wrong output path can overwrite disks or important files.

Syntax

dd if=input of=output [operands...]

Parameters

• if=INPUT: Input file or device. Defaults to standard input.
• of=OUTPUT: Output file or device. Defaults to standard output.
• bs=SIZE: Block size for reads and writes.
• count=N: Copy N input blocks.
• skip=N: Skip N input blocks before copying.
• seek=N: Skip N output blocks before writing.

Common Options

• status=progress: Show progress on GNU dd.
• conv=fsync: Flush output data before finishing.
• conv=noerror,sync: Continue after read errors and pad blocks. Useful for damaged media, but understand the result.
• iflag=fullblock: Read full input blocks where useful.

Examples

sudo dd if=ubuntu.iso of=/dev/sdX bs=4M status=progress conv=fsync

Write an ISO image to a USB drive. Replace /dev/sdX carefully.

dd if=/dev/zero of=test.img bs=1M count=100

Create a 100 MiB zero-filled file.

sudo dd if=/dev/sda of=disk.img bs=64K status=progress

Copy a disk into an image file.

dd if=file.bin bs=1 count=16 | hexdump -C

Read the first 16 bytes of a file.

Practical Notes

• Always verify device names with lsblk before writing to block devices.
• of=/dev/sdX writes to a whole disk, not a partition.
• Prefer specialized tools when they provide safer prompts for image writing.