How to Use the Command 'iostat' (with Examples)

The iostat command is a versatile tool used to report statistics related to the performance of CPU and I/O devices. It provides valuable insights into how system resources are being utilized by displaying information such as the amount of data transfer, the frequency of transfers, and the system’s CPU load averages. This command is commonly used by system administrators and power users to monitor and troubleshoot system performance issues, especially those related to disk I/O bottlenecks.

Use Case 1: Display Snapshot Device and CPU Statistics

Code:

iostat

Motivation:
This use case is ideal when you want a quick snapshot overview of your system’s current performance. By running iostat, you receive immediate feedback on how well your devices and CPU are performing. It provides a comprehensive report that combines device statistics with CPU utilization and system load averages, which can be used to identify potential hotspots or existing performance bottlenecks.

Explanation:
The command iostat is run without any options, prompting it to display default statistics that include kilobytes per transfer, transfers per second, and megabytes per second for the devices. It also shows the CPU usage percentage distributed across user mode, system mode, and idle time, along with load averages for the past 1, 5, and 15 minutes.

Example Output:

          disk0              cpu    load average
    KB/t tps  MB/s  us sy id   1m   5m   15m
   23.00  77  1.75   7  5 88  0.30 0.28 0.27

Use Case 2: Display Only Device Statistics

Code:

iostat -d

Motivation:
Focusing solely on device statistics can be beneficial when troubleshooting disk-related performance issues. By minimizing the report to include only device-specific data, iostat -d helps reduce clutter and highlights how each disk is performing in terms of data transfer rates and efficiency.

Explanation:
The -d flag instructs iostat to show only the device activity section of its output, omitting any CPU statistics. This makes the output simpler and easier to compare when you need precise data about the utilization of your disks.

Example Output:

          disk0       
    KB/t tps  MB/s 
   23.00  77  1.75 

Use Case 3: Display Incremental Reports Every 2 Seconds

Code:

iostat 2

Motivation:
When real-time monitoring of system performance is required, incremental reporting provides ongoing updates. By setting up the iostat command to report every 2 seconds, you can watch for transient issues as they occur, allowing for timely intervention if necessary.

Explanation:
Providing a single numeric argument, 2, tells iostat to continually update the performance statistics every two seconds. The continuous update serves as a live feed of performance data until the command is manually stopped.

Example Output:

          disk0              cpu    load average
    KB/t tps  MB/s  us sy id   1m   5m   15m
   23.00  77  1.75   7  5 88  0.30 0.28 0.27
   24.00  80  1.83   8  6 86  0.32 0.29 0.28
   ...

Use Case 4: Display Statistics for the First Disk Every Second Indefinitely

Code:

iostat -w 1 disk0

Motivation:
This use case is particularly useful for isolating the performance of a specific disk without interruption. By monitoring disk0 every second, you can gather detailed information about its activity, useful for both performance tuning and diagnosing issues exclusive to this disk.

Explanation:
The -w 1 argument specifies that updates should be shown every second. Adding disk0 focuses the monitoring to just the first disk (commonly the system’s main drive), providing detailed and real-time performance data of this particular disk’s operations.

Example Output:

          disk0       
    KB/t tps  MB/s 
   23.00  77  1.75 
   24.00  78  1.82 
   ...

Use Case 5: Display Statistics for the Second Disk Every 3 Seconds, 10 Times

Code:

iostat -w 3 -c 10 disk1

Motivation:
In certain situations, you may need to observe how a disk behaves over a specific number of intervals. This command captures data every 3 seconds, limiting the observation period to 10 cycles, thereby helping to succinctly capture or log the performance of disk1.

Explanation:
Here, -w 3 sets the collection interval to 3 seconds, while -c 10 tells iostat to cap the number of updates at 10. Combined with disk1, this command succinctly records how the second disk is performing over a defined topical period, which can be valuable for reports or analysis.

Example Output:

          disk1       
    KB/t tps  MB/s 
   20.00  70  1.50 
   21.00  73  1.55 
   ...

Use Case 6: Display Using Old-Style iostat Output

Code:

iostat -o

Motivation:
With time and updates, the output style of commands like iostat evolves. For users familiar with previous presentation formats or requiring consistent historical data comparison, the -o flag provides a classic output style, aiding in continuity and compatibility with older workflows.

Explanation:
The -o flag configures iostat to present data in its former style, highlighting metrics like sectors per second in place of the kilobytes per transfer and including load averages more explicitly alongside CPU statistics.

Example Output:

          disk0              cpu    load average
    sec/t tps  MB/s  us sy id   1m   5m   15m
   23    77  1.75   7  5 88  0.30 0.28 0.27

Use Case 7: Display Total Device Statistics

Code:

iostat -I

Motivation:
System administrators seeking cumulative data over the lifetime of their system’s operation will find the total device statistics provided by iostat -I to be highly beneficial. It collates the total transferred data, giving a macro view of I/O operations, essential for capacity planning and historical analysis.

Explanation:
The -I flag shifts the reporting to display total statistics over time rather than increments. It shows the accumulated kilobytes per transfer, total number of transfers, and total megabytes transferred, offering insights into how much work your devices have undertaken over their lifetime.

Example Output:

          disk0       
  total  KB/t xfrs   MB   
   5400 23.00  157  3700 

Conclusion:

The iostat command offers a wealth of information to assess and manage the performance of your CPU and I/O devices with clear, customizable outputs. By grasping its various use cases and corresponding options, you can tailor the monitoring to match specific needs—be it quick insights, continuous observation, or cumulative performance tracking—for efficient system administration.