What is dd?
dd is known as an abbreviation for 'Data Description' or 'Disk Dump'. Unlike conventional copying (`cp`), it's used to directly manipulate hardware devices (disks, USBs) or to replicate raw data bit by bit.
Core Syntax Structure
Options are used in `key=value` format without preceding hyphens (-).
- if (Input File): The input source. (Original file, ISO image, disk device to read from, etc.)
- of (Output File): The output destination. (Location to copy to, USB device, backup file, etc.) **This is the most critical option.**
- bs (Block Size): The amount of data to read and write at once. (e.g., 4M, 1G). Affects speed.
⚠️ Warning: Must Check Before Use
If you accidentally specify a system hard drive for `of=` (output destination), your operating system and data will be instantly erased. Always confirm the device path (e.g., `/dev/sdb`) using the `lsblk` command.
Key Options (Shell)
The order of dd options is not critical, but typically `if` > `of` > `bs` > `status` is used.
1. Input/Output Specification (Required)
2. Size and Speed Control
3. Data Conversion and Control
Generated command:
Try combining the commands.
Description:
`dd` Executes the command.
Combine the above options to virtually execute commands with AI.
Usage Scenario Examples
Common dd command patterns used in practice.
Creating a Bootable USB
sudo dd if=ubuntu-22.04.iso of=/dev/sdb bs=4M status=progressBurns an ISO file to a USB device (assuming `/dev/sdb`). `bs=4M` is for speed improvement.
Full Disk Backup (Image Creation)
sudo dd if=/dev/sda of=~/backup.img bs=64K status=progressCreates an image file `backup.img` from the entire `/dev/sda` disk.
Completely Wiping a Disk
sudo dd if=/dev/urandom of=/dev/sdX bs=1M status=progressOverwrites a disk (`/dev/sdX`) with random data, making recovery impossible.
Creating an Empty File of Specific Size
dd if=/dev/zero of=testfile_1GB bs=1G count=1Creates a 1GB empty file (filled with zeros) for testing purposes.
Tips & Precautions
Useful Tips
- sudo Permissions: `sudo` is absolutely necessary when dealing with hardware devices (/dev/...).
- /dev/zero and /dev/urandom: `if=/dev/zero` outputs an infinite stream of zeros, and `if=/dev/urandom` outputs an infinite stream of random data. These are special files.
- Finding USB Devices: Before and after plugging in a USB, use the `lsblk` command to accurately identify the newly appearing device name (e.g., sdb, sdc).