Hard Drive Acquisition with DD

G5 Cyber Security

2 weeks ago

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

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.

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

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.

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.

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.