CHFI Incident Response and First Responder Skills Practice Question

During an incident response, a first responder needs to collect evidence from a Linux server that is still running. The server has sensitive data and cannot be shut down. Which technique is BEST for acquiring a forensic image of the hard disk?

⚠ Common exam trap

EC-Council often tests the misconception that conv=noerror,sync is always required for forensic imaging, but in a live, healthy server scenario, it can introduce artifacts and is not the best practice.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Use dd if=/dev/sda of=/mnt/evidence/image.dd bs=4M

It uses dd with a 4M block size, which improves acquisition speed while still producing a bit-for-bit forensic image of the entire disk (/dev/sda). The conv=noerror,sync option in A is unnecessary for a live acquisition from a healthy disk and can mask read errors, while B's larger block size is more efficient for imaging a running system without shutdown.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Use dd if=/dev/sda of=/mnt/evidence/image.dd conv=noerror,sync
Why it's wrong here
This command uses conv=noerror,sync, which instructs dd to continue after read errors and replace the unreadable sectors with null bytes. That padding alters the bit-for-bit integrity of the forensic image and masks physical or media damage, so the output hash will never match the original disk. Standard forensic acquisition avoids these flags specifically so any read error aborts the process and is documented, rather than being silently filled with zeros.
✓
Use dd if=/dev/sda of=/mnt/evidence/image.dd bs=4M
Why this is correct
Imaging the entire block device /dev/sda with bs=4M captures the complete physical disk, including the master boot record, partition tables, each partition, and unallocated space. The bs=4M argument is only a performance optimization that increases the read/write buffer size; it does not change the output data, so the result is still a bit-for-bit forensically sound copy. This is the correct first-responder action because it preserves all potential evidence on the drive.
✗
Use dd if=/dev/mapper/root of=/mnt/evidence/image.dd
Why it's wrong here
/dev/mapper/root is a device-mapper logical volume node exposed by LVM, not the raw physical disk. Copying it only captures that one logical volume and omits other logical volumes, volume group metadata, physical volume headers, and any unallocated space outside the LV. For a forensic image, you must acquire the whole physical device, because valuable evidence can reside in areas not represented by a single mapper device.
✗
Use dd if=/dev/sda1 of=/mnt/evidence/image.dd
Why it's wrong here
/dev/sda1 is a single partition, so this command would omit the master boot record, the partition table, and all other partitions on the disk. A partition-level image may be appropriate only if the scope is strictly that filesystem, but an incident response investigation demands a complete physical-disk image to recover deleted data and artifacts from unallocated space. The target must be the entire disk /dev/sda, not merely one of its partitions.

Go deeper

CHFI Incident Response and First Responder Skills Practice Question

Why each option matters

Option-by-option breakdown

Related to this question