Hard Drive Acquisition with DD

TL;DR

Yes, dd can be used to acquire a hard drive, but it’s crucial to understand the risks and use it correctly. Incorrect usage can easily overwrite data. This guide explains how to do it safely.

Acquiring a Hard Drive with DD: A Step-by-Step Guide

1. Identify the Target Drive
• First, you must correctly identify the drive you want to image. Using the wrong device name will result in data loss on the incorrect drive!
• Use lsblk or fdisk -l to list all connected block devices. Be very careful when interpreting the output. Pay attention to size and labels.

sudo lsblk

sudo fdisk -l

• Example Output (lsblk):

  NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
  disk0   8:0    0 238.5G  0 disk 
  sda    8:16   0 238.5G  0 disk 
  sda1   8:17   0 512M  0 part /boot/efi
  sda2   8:18   0 237.9G  0 part /

  In this example, disk0 is the physical drive and sda is a common device name for it.

• Double-check! If you’re unsure, disconnect other drives temporarily to avoid mistakes.
2. Unmount the Drive
• Before imaging, unmount any partitions on the target drive. This prevents file system inconsistencies during the acquisition process.
• Use umount followed by the mount point(s) identified in the output of lsblk or df -h.

sudo umount /dev/sda1

sudo umount /dev/sda2

3. Run the DD Command
• The basic dd command for a full disk image is:

sudo dd if=/dev/sdX of=/path/to/image.img bs=4M status=progress

• Replace /dev/sdX with the correct device name (e.g., /dev/sda).
• Replace /path/to/image.img with the desired path and filename for the image file. Ensure you have enough space on the destination drive!
• bs=4M sets the block size to 4MB, which is a good balance between speed and efficiency.
• status=progress shows the progress of the imaging process (available in newer versions of dd). If your version doesn’t support this, you can send a SIGUSR1 signal to the dd process to get status updates.
• Important: Consider using conv=sync,noerror for more robust imaging, especially with failing drives.

  sudo dd if=/dev/sdX of=/path/to/image.img bs=4M conv=sync,noerror status=progress

  • conv=sync pads every input block with zeros to a fixed size.
  • conv=noerror continues copying even if read errors occur (useful for damaged drives). Errors will be reported.
4. Verify the Image
• After the imaging process is complete, it’s crucial to verify the integrity of the image. Use md5sum or sha256sum to generate a checksum of both the source drive and the image file.

sudo md5sum /dev/sdX

sudo md5sum /path/to/image.img

sudo sha256sum /dev/sdX

sudo sha256sum /path/to/image.img

• Compare the checksums. They must match exactly for a valid image.
5. Important Considerations
• Data Loss Risk: Incorrectly specifying the input or output device can lead to irreversible data loss. Double-check everything before running the command!
• Space Requirements: The image file will be the same size as the entire source drive, even if it’s mostly empty. Ensure you have enough storage space available.
• Time: Imaging a large hard drive can take a significant amount of time (hours or even days).
• cyber security implications: Be aware that imaging a drive creates a complete copy, including any malware or sensitive data. Handle the image file securely.