# dd — Copy, Clone and Wipe Drives Block by Block > Practical guide to dd — create disk images, clone drives, write ISOs to USB, wipe disks and copy raw block data, with the safety notes this tool demands. Source: https://www.jpkc.com/db/en/cheatsheets/shell-system/dd/ dd copies data block by block straight at the device level — perfect for disk images, cloning whole drives, building bootable USB sticks or securely wiping disks. That same power makes it dangerous: dd has earned the nickname "disk destroyer" for good reason. Swap `if=` and `of=`, or point `of=/dev/sdX` at the wrong disk, and you overwrite an entire drive instantly and irreversibly — no prompt, no trash can, no undo. Always confirm the target device with `lsblk` before you press Enter. ## Basic Usage `dd if= of=` — Copy data from input file to output file. ```bash dd if=/dev/sda of=/dev/sdb ``` `dd if= of= bs=` — Copy with a specific block size (affects speed). ```bash dd if=/dev/sda of=disk.img bs=4M ``` `dd if= of= bs= count=` — Copy only N blocks of the specified size. ```bash dd if=/dev/zero of=testfile bs=1M count=100 ``` `dd if= of= status=progress` — Show transfer progress during copy. ```bash dd if=/dev/sda of=backup.img bs=4M status=progress ``` `dd if= of= conv=` — Apply conversion options during copy. ```bash dd if=data.txt of=upper.txt conv=ucase ``` ## Disk Images & Cloning `dd if= of= bs=4M status=progress` — Create a raw disk image from a device. ```bash dd if=/dev/sda of=disk-backup.img bs=4M status=progress ``` `dd if= of= bs=4M status=progress` — Restore a disk image to a device. ```bash dd if=disk-backup.img of=/dev/sda bs=4M status=progress ``` `dd if= bs=4M status=progress | gzip > .gz` — Create a compressed disk image. ```bash dd if=/dev/sda bs=4M status=progress | gzip > disk-backup.img.gz ``` `gunzip -c .gz | dd of= bs=4M status=progress` — Restore a compressed disk image. ```bash gunzip -c disk-backup.img.gz | dd of=/dev/sda bs=4M status=progress ``` `dd if= of= bs=4M conv=noerror,sync status=progress` — Clone a disk (skip errors, pad with zeros). ```bash dd if=/dev/sda of=/dev/sdb bs=4M conv=noerror,sync status=progress ``` ## Bootable USB & ISO `dd if= of= bs=4M status=progress oflag=sync` — Write an ISO image to a USB drive. ```bash dd if=ubuntu-24.04-desktop-amd64.iso of=/dev/sdb bs=4M status=progress oflag=sync ``` `dd if= of= bs=4M status=progress` — Create an ISO from a CD/DVD drive. ```bash dd if=/dev/cdrom of=disc.iso bs=4M status=progress ``` `dd if=/dev/zero of= bs=512 count=1` — Wipe the MBR (first 512 bytes) of a disk. ```bash dd if=/dev/zero of=/dev/sdb bs=512 count=1 ``` ## Generate Test Files `dd if=/dev/zero of= bs=1M count=` — Create a file filled with zeros of a specific size. ```bash dd if=/dev/zero of=100mb.bin bs=1M count=100 ``` `dd if=/dev/urandom of= bs=1M count=` — Create a file filled with random data. ```bash dd if=/dev/urandom of=random.bin bs=1M count=50 ``` `dd if=/dev/zero of= bs=1 count=0 seek=` — Create a sparse file (allocates space without writing). ```bash dd if=/dev/zero of=sparse.img bs=1 count=0 seek=10G ``` ## Wipe & Secure Erase `dd if=/dev/zero of= bs=4M status=progress` — Wipe a disk with zeros. ```bash dd if=/dev/zero of=/dev/sdb bs=4M status=progress ``` `dd if=/dev/urandom of= bs=4M status=progress` — Overwrite a disk with random data (more secure). ```bash dd if=/dev/urandom of=/dev/sdb bs=4M status=progress ``` `dd if=/dev/zero of= bs=4M; rm ` — Overwrite a file before deleting it. ```bash dd if=/dev/zero of=secret.txt bs=4M; rm secret.txt ``` ## Benchmark & Performance `dd if=/dev/zero of= bs=1G count=1 oflag=dsync` — Benchmark write speed (sync after each block). ```bash dd if=/dev/zero of=/tmp/testfile bs=1G count=1 oflag=dsync ``` `dd if= of=/dev/null bs=1M` — Benchmark read speed (discard output). ```bash dd if=/tmp/testfile of=/dev/null bs=1M ``` `dd if=/dev/zero of= bs= count= oflag=direct` — Test direct I/O write speed (bypass cache). ```bash dd if=/dev/zero of=/tmp/testfile bs=4M count=256 oflag=direct ``` ## Options & Flags `bs=` — Block size for read and write (K, M, G suffixes). Larger = faster. ```bash bs=4M (common for disk operations) ``` `count=` — Copy only N input blocks. ```bash count=100 (with bs=1M = 100 MB) ``` `skip=` — Skip N blocks at the start of input. ```bash skip=1 bs=512 (skip MBR) ``` `seek=` — Skip N blocks at the start of output. ```bash seek=1 bs=512 (write after MBR) ``` `conv=noerror,sync` — Continue on read errors and pad with zeros (for damaged disks). ```bash dd if=/dev/sda of=rescue.img conv=noerror,sync bs=4K ``` `oflag=sync` — Synchronize output after each write (ensures data is flushed). ```bash dd if=image.iso of=/dev/sdb bs=4M oflag=sync ``` `iflag=fullblock` — Accumulate full input blocks (prevents short reads from pipes). ```bash dd if=/dev/stdin of=output.bin bs=1M iflag=fullblock ``` ## Conclusion dd is one of the most powerful — and most dangerous — tools in the Unix world: it writes blindly to exactly where you tell it, with no confirmation and no undo. A wrong `of=/dev/sdX` destroys an entire disk in seconds. So **always** verify the target device first with `lsblk` or `fdisk -l`, never swap `if=` and `of=`, and unmount the device before writing. Use `status=progress` for visible progress, a sensible `bs=` (usually `4M`) for throughput, and `conv=fsync` or `oflag=sync` so all data actually lands on the medium instead of sitting in the cache. On macOS, address the raw device `/dev/rdiskN` (much faster) and unmount it first with `diskutil unmountDisk`. When in doubt, check one more time rather than overwriting a disk you can never get back. ## Further Reading - [Arch Wiki: dd](https://wiki.archlinux.org/title/Dd) – thorough reference covering disk images, cloning and secure erasing - [Wikipedia: dd (Unix)](https://en.wikipedia.org/wiki/Dd_(Unix)) – background, options and common usage patterns ## Related Commands - [lsblk](https://www.jpkc.com/db/en/cheatsheets/shell-system/lsblk/) – list block devices; use it to verify the target before any dd write - [fdisk](https://www.jpkc.com/db/en/cheatsheets/shell-system/fdisk/) – view and edit partition tables - [mount](https://www.jpkc.com/db/en/cheatsheets/shell-system/mount/) – mount and unmount filesystems (unmount before dd)