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dd

The dd command in Linux is a powerful utility for low-level data copying and conversion, primarily used for disk cloning, creating disk images, partition backups, and writing ISO files to USB drives. Mastering the dd command is essential for Linux system administrators, as it enables precise control over data manipulation, backup processes, and disk recovery.

Option Description Example
if= Input file or device (e.g., disk or ISO) if=/dev/sda
of= Output file or device (e.g., target disk or image file) of=/dev/sdb
bs= Block size for input/output operations bs=4M
status= Display the status of the operation status=progress
conv= Conversion options (e.g., noerror, sync) conv=noerror,sync
seek= Skip blocks in the output file seek=1
count= Limit the number of blocks to copy count=100

Speedtest a harddrive

dd if=/dev/zero of=testfile bs=1G count=1 oflag=direct status=progress

Copy a drive to another (works for uefi)

dd if=/dev/sda of=/dev/sdb bs=32M status=progress

Create a 500mb file

dd if=/dev/zero of=fil_500mb.bin bs=1M count=500

Output your microphone to a remote computer's speaker

This will output the sound from your microphone port to the ssh target computer's speaker port. The sound quality is very bad, so you will hear a lot of hissing.

dd if=/dev/dsp | ssh -c arcfour -C username@host dd of=/dev/dsp

Processor / memory bandwidthd in GB/s

Read 32GB zero's and throw them away. How fast is your system?

dd if=/dev/zero of=/dev/null bs=1M count=32768

Create an emergency swapfile when the existing swap space is getting tight

dd if=/dev/zero of=/swapfile bs=1024 count=1024000
mkswap /swapfile
swapon /swapfile

Efficient remote forensic disk acquisition gpg-crypted for multiple recipients

dd if=/dev/sdb | pigz | gpg -r <recipient1> -r <recipient2> -e --homedir /home/to/.gnupg | nc remote_machine 1337

Wipe a failed disk - If you can't use shred or ddrescue, this is a very slow but portable alternative

i=0
while true ; do
  echo "Writing block $i"
  dd if=/dev/zero of=/dev/sda count=1 bs=1 seek="$i"
  let i=i+1
done

Wipe first and last 1G of a hard disk

dd bs=4096 if=/dev/zero of=/dev/sdx count=256 seek=$(( $(blockdev --getsz /dev/sdx) - 256))

uuid generator

dd if=/dev/urandom bs=16 count=1 2>/dev/null \
| tr -dc '0-9a-f' </dev/urandom | head -c 32 \
| fold -w 4 \
| paste -sd '' - \
| sed 's/^\(........\)\(....\)\(....\)\(....\)\(............\)$/\1-\2-\3-\4-\5/'

Resource(s)