iotop

iotop

The iostat command in Linux is used to monitor system input/output (I/O) statistics for devices and partitions. It provides a snapshot of CPU utilization and I/O activity, including disk utilization, CPU utilization, and I/O wait times. Here's a detailed explanation of how to use iostat and what information it provides:

Usage of iostat

Basic Usage

To use iostat, simply open a terminal and type:

iostat

By default, iostat displays statistics since the last reboot. It outputs statistics for CPU, individual devices (disks), and partitions.

Options and Output

1. CPU Utilization:

   • us: Percentage of CPU utilization that occurred while executing at the user level (application).

   • sy: Percentage of CPU utilization that occurred while executing at the system (kernel) level.

   • id: Percentage of CPU time that was idle and not executing any tasks.

   • wa: Percentage of CPU time spent waiting for I/O operations to complete.

   • st: Percentage of CPU time stolen from a virtual machine.

   Example output for CPU:

   avg-cpu:  %user   %nice %system %iowait  %steal   %idle
             11.04    0.05    2.37    0.25    0.00   86.29

2. Device Utilization:

   • tps: Number of transfers per second that were issued to the device.

   • kB_read/s: Amount of data read from the device in kilobytes per second.

   • kB_wrtn/s: Amount of data written to the device in kilobytes per second.

   • kB_read: Total number of kilobytes read from the device.

   • kB_wrtn: Total number of kilobytes written to the device.

   Example output for devices:

   Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
   sda               0.00         0.00         0.00          0          0
   sdb               0.00         0.00         0.00          0          0

Additional Options

• Interval: You can specify the interval in seconds for which iostat displays statistics. For example, to refresh every 2 seconds:

  iostat 2

• Device Filtering: You can filter output by specific devices or partitions. For example, to monitor only sda:

  iostat -d sda

• Extended Statistics: Use -x option to display extended statistics including average queue length and utilization percentages for each CPU and device:

  iostat -x

Use Cases

• Performance Monitoring: iostat is valuable for monitoring disk and CPU performance metrics over time, identifying bottlenecks, and troubleshooting performance issues.

• Capacity Planning: Helps in capacity planning by providing insights into disk utilization and throughput, aiding decisions on hardware upgrades or optimizations.

• Scripting and Automation: Output from iostat can be parsed and integrated into scripts or monitoring tools for automated performance monitoring.

Conclusion

iostat is a versatile command-line tool for monitoring system I/O performance and CPU utilization on Linux systems. Understanding its output and options allows system administrators and users to diagnose performance issues, optimize system resources, and make informed decisions about system maintenance and upgrades.

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