XK0-006 Troubleshooting Practice Question
A Linux technician is troubleshooting a system that is experiencing high disk I/O wait times. Which TWO commands can be used to identify disk I/O performance issues? (Choose two.)
⚠ Common exam trap
XK0-006 often tests the confusion between memory tools (free), file tools (lsof), and kernel log tools (dmesg) versus the actual I/O performance tools (vmstat, iostat, iotop).
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
✓
vmstat
Option B (vmstat) is correct because it reports virtual memory statistics including the 'wa' (I/O wait) column in its CPU breakdown, which directly shows the percentage of time the CPU spent waiting on disk I/O, making it ideal for diagnosing high I/O wait times. Option C (iostat) is correct because it is specifically designed to report per-device and per-partition disk I/O statistics such as tps, kB_read/s, kB_wrtn/s, and %util, which pinpoint which block devices are saturated. Option A (lsof) lists open files and the processes using them, which can hint at file usage but does not measure disk I/O performance or wait times. Option D (free -h) only displays memory and swap usage in human-readable form, providing no direct disk I/O metrics. Option E (dmesg) shows kernel ring buffer messages, useful for hardware or driver errors, but it does not report ongoing disk I/O performance statistics.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
lsof
Why it's wrong here
lsof lists open files and the processes holding them, which identifies what is using a filesystem rather than reporting disk latency or queue depth. It is tempting because a process holding a deleted file can cause I/O pressure, so lsof is the right tool when hunting the specific process pinning a mount.
- ✓
vmstat
Why this is correct
vmstat reports run-queue, blocked-process and CPU columns including wa (I/O wait), letting the technician confirm whether processes are stalled on disk. Its r and b columns distinguish CPU saturation from storage-bound waiting, directly addressing the high I/O wait symptom.
- ✓
iostat
Why this is correct
iostat reports per-device throughput, utilisation and average queue length plus await, exposing disks saturated by I/O. The %util and await metrics directly identify the device causing the elevated I/O wait times described in the stem.
- ✗
free -h
Why it's wrong here
free -h reports memory and swap usage, not disk latency, throughput or queue depth, so it cannot show which block device is saturated. It is tempting because heavy swapping drives disk I/O, making free the correct starting point when memory exhaustion is the suspected root cause.
- ✗
dmesg
Why it's wrong here
dmesg prints kernel ring-buffer messages such as driver and hardware errors; it does not report per-device I/O latency or utilisation. It is tempting because I/O errors and resets do appear there, so dmesg is the right choice when you suspect failing hardware or a driver fault rather than load.
Go deeper
Related to this question
Learn chapter
System Troubleshooting and Performance Tuning
Key term
Linux
Linux is an open-source operating system that manages computer hardware and software, widely used in servers, desktops, and embedded systems.
Key term
dmesg
dmesg is a Linux command that displays messages from the kernel ring buffer, used to diagnose hardware and boot issues.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.