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dd

Linux · Files · reference only

What it does

Copies and converts data block by block between files and devices. It is used to clone disks, create images or generate test files.

Syntax

dd [operando=valor]...

Options and parameters

  • if=fichero

    Input file or device; if omitted, it reads from standard input.

  • of=fichero

    Output file or device; if omitted, it writes to standard output.

  • bs=tamaño

    Block size for reading and writing, such as 4M.

  • count=N

    Copies only N input blocks.

  • skip=N

    Skips N blocks at the start of the input.

  • seek=N

    Skips N blocks at the start of the output.

  • status=progress

    Shows copy progress while it works.

  • conv=fsync

    Forces the data to be physically written before finishing.

Usage examples

  • dd if=/dev/zero of=vacio.img bs=1M count=10

    Creates a 10 MiB file filled with zeros.

  • dd if=disco.img of=copia.img bs=4M status=progress

    Copies an image while showing progress.

  • dd if=/dev/urandom of=aleatorio.bin bs=1K count=64

    Creates a 64 KiB file of random data.

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

    Writes an image to a USB device. Replace sdX with great care.

Notes and common mistakes

  • dd does not ask for confirmation: a wrong of= on a device such as /dev/sda destroys its data without warning.
  • That is why it is jokingly called the disk destroyer; in the simulator it is safe to practice.
  • Always check the target device with lsblk before writing.

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