This CHFI practice question tests your understanding of computer forensics fundamentals and process. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
During a forensic investigation, an analyst creates a bit-for-bit copy of a suspect's hard drive using the 'dd' command with the following parameters: dd if=/dev/sda of=/evidence/image.dd bs=4k conv=noerror,sync. What is the purpose of 'conv=noerror,sync'?
To hash the output image
Why wrong: Hashing is done separately, not with conv=noerror,sync.
To ensure the command runs with superuser privileges
Why wrong: Superuser privileges are needed anyway; conv=noerror,sync does not control privileges.
To ignore read errors and pad with zeros
Correct. This ensures the image is complete despite errors.
To compress the output image
Why wrong: Compression is not achieved with noerror,sync.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
To ignore read errors and pad with zeros
Option C is correct because 'conv=noerror,sync' tells dd to continue reading even when encountering read errors (noerror) and to pad the output with zeros (sync) to maintain the same total size as the original drive. This ensures a complete forensic image is created despite bad sectors, preserving the integrity of the acquisition for analysis.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
To hash the output image
Why it's wrong here
Hashing is done separately, not with conv=noerror,sync.
To ensure the command runs with superuser privileges
Why it's wrong here
Superuser privileges are needed anyway; conv=noerror,sync does not control privileges.
To ignore read errors and pad with zeros
Why this is correct
Correct. This ensures the image is complete despite errors.
Related concept
Read the scenario before looking for a memorised answer.
To compress the output image
Why it's wrong here
Compression is not achieved with noerror,sync.
Common exam traps
Cisco often tests the misconception that 'sync' refers to flushing disk caches (like the sync command) rather than its actual function of padding output with null bytes on read errors.
Detailed technical explanation
Under the hood, when dd encounters a read error on a bad sector, the kernel returns an error code; with 'noerror', dd ignores that error and continues to the next block. The 'sync' option then writes a block of zeros (equal to the input block size, here 4 KiB) to the output image in place of the unreadable data, ensuring the image remains exactly the same size as the source and preserving the logical block addressing (LBA) layout. In real-world forensics, this is critical because a single bad sector can halt acquisition without these flags, potentially losing evidence from surrounding sectors.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
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FAQ
Computer Forensics Fundamentals and Process — This question tests Computer Forensics Fundamentals and Process — Read the scenario before looking for a memorised answer..
The correct answer is: To ignore read errors and pad with zeros — Option C is correct because 'conv=noerror,sync' tells dd to continue reading even when encountering read errors (noerror) and to pad the output with zeros (sync) to maintain the same total size as the original drive. This ensures a complete forensic image is created despite bad sectors, preserving the integrity of the acquisition for analysis.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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