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CompTIA Linux+ (XK0-006)System ManagementHard

An application on a Linux server is running slowly, and a technician suspects disk I/O is the bottleneck. Which command provides extended per-device I/O statistics, including average wait time (await) and percentage of CPU time the device was busy (%util)?

  1. Afree -h
  2. Btop
  3. Ciostat -x 2
  4. Dvmstat 2
Show answer & explanation

Correct answer: C. iostat -x 2

'iostat -x' provides extended statistics per block device, including await, svctm, and %util, refreshed every 2 seconds in this example, making it the correct tool for diagnosing disk I/O bottlenecks. 'vmstat' reports overall system stats without per-device breakdown, 'free' reports memory usage, and 'top' focuses on process CPU/memory usage rather than disk I/O details.

Why the other options are wrong

  • A. Shows memory and swap usage, unrelated to disk I/O performance.
  • B. Focuses on process-level CPU and memory usage, not disk device statistics.
  • D. Reports overall virtual memory, CPU, and generic I/O stats but no per-device breakdown.

iostat -x

Command from the sysstat package that reports extended I/O statistics per block device, useful for diagnosing storage bottlenecks.

  • %util shows how busy a device is
  • await is average time for I/O requests to complete
  • Requires the sysstat package to be installed

Memory trick: iostat -x = X-ray vision into disk device health.

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