Quick Answer
The answer is `ps --sort=-rss` and `ps -ef | sort -k5 -rn`. The first command uses the native `--sort` flag with a minus sign prefix to sort the process list by resident set size (RSS) in descending order, which is the most reliable method because it avoids column alignment issues that can occur when piping to `sort`. The second command pipes the output of `ps -ef` to `sort -k5 -rn`, where `-k5` targets the fifth column (RSS) and `-rn` performs a reverse numeric sort. On the LPIC-1 exam, this tests your understanding of process monitoring and command-line text processing; a common trap is forgetting that `ps -ef` output may have inconsistent spacing, making the pipe to `sort` less dependable than the native `ps` sort option. A helpful memory tip: think of the minus sign in `--sort=-rss` as a downward arrow pointing to "reverse" order, ensuring the largest RSS values appear first.
This LPIC-1 practice question tests your understanding of shells, scripting and data management. 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.
Which TWO commands can be used to sort the output of ps -ef by the resident set size (RSS) in descending order?
ps -ef | sort -k5,5 -rn
Why wrong: This is redundant and still sorts by the 5th field, but option D is more common.
ps --sort=-rss
--sort=-rss sorts by RSS descending.
ps -ef | sort -k3 -rn
Why wrong: -k3 is PID, not RSS.
ps --sort=rss
Why wrong: This sorts by RSS ascending, not descending.
ps -ef | sort -k5 -rn
RSS is typically the 5th field in ps -ef output.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
ps --sort=-rss
Option B is correct because `ps --sort=-rss` directly sorts the process list by resident set size (RSS) in descending order, using the minus sign prefix to indicate reverse sort. This is a native `ps` feature that avoids piping to `sort`, which can be less reliable due to column alignment issues.
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.
ps -ef | sort -k5,5 -rn
Why it's wrong here
This is redundant and still sorts by the 5th field, but option D is more common.
ps --sort=-rss
Why this is correct
--sort=-rss sorts by RSS descending.
Related concept
Read the scenario before looking for a memorised answer.
ps -ef | sort -k3 -rn
Why it's wrong here
-k3 is PID, not RSS.
ps --sort=rss
Why it's wrong here
This sorts by RSS ascending, not descending.
ps -ef | sort -k5 -rn
Why this is correct
RSS is typically the 5th field in ps -ef output.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse the field number for RSS in `ps -ef` output (it is the 5th field, not the 3rd) and may overlook that `--sort=rss` defaults to ascending order, requiring a minus sign for descending.
Detailed technical explanation
The `ps` command's `--sort` option accepts a comma-separated list of sort keys, with a leading minus sign for descending order. RSS (resident set size) represents the non-swapped physical memory a process has used, typically shown in kilobytes. Using `ps -ef | sort -k5 -rn` (option E) works because the 5th field in `ps -ef` output is RSS, and `-rn` performs a numeric reverse sort; however, this can be fragile if field widths vary or if headers are included, making the native `ps` sort more robust.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Shells, Scripting and Data Management — This question tests Shells, Scripting and Data Management — Read the scenario before looking for a memorised answer..
The correct answer is: ps --sort=-rss — Option B is correct because `ps --sort=-rss` directly sorts the process list by resident set size (RSS) in descending order, using the minus sign prefix to indicate reverse sort. This is a native `ps` feature that avoids piping to `sort`, which can be less reliable due to column alignment issues.
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 11, 2026
This LPIC-1 practice question is part of Courseiva's free LPI certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LPIC-1 exam.
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