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Sar

System Activity Reporter sar

The sar (System Activity Reporter) command in Linux is a powerful tool for monitoring system performance. It collects, reports, and saves system activity information, making it a valuable utility for analyzing the performance of CPU, memory, disk, and network activities over time.

Basic Usage of sar

Here are some essential sar commands and their use cases:

  • Basic CPU Usage Monitoring

To monitor CPU usage at 1-second intervals for 5 iterations:

bash sar 1 5

  • The first argument (1) specifies the interval in seconds between each report.
  • The second argument (5) specifies the number of reports to generate.

This command outputs CPU usage statistics such as user time, system time, and idle time at each interval.

  • Monitoring Disk Activity

To monitor disk activity at 1-second intervals for 5 iterations:

bash sar -d 1 5

  • -d: Reports disk activity statistics, including read/write operations per second and average request size.

This command provides a snapshot of disk performance, helping identify I/O bottlenecks or issues with disk utilization.

Understanding sar Output

The output of sar varies depending on the options used. Here's a brief overview of common metrics:

  • CPU Metrics:
  • %user: Percentage of CPU utilization that occurred while executing user-level code.
  • %system: Percentage of CPU utilization that occurred while executing system-level code.

  • %idle: Percentage of CPU time spent idle.

  • Disk Metrics:

  • tps: Transfers per second (I/O operations).
  • rd_sec/s: Number of sectors read per second.
  • wr_sec/s: Number of sectors written per second.
  • avgrq-sz: Average size (in sectors) of the requests that were issued to the device.

Practical Use Cases

  • Real-Time CPU Monitoring: Use sar to get a quick overview of CPU usage in real-time, which can help identify processes that are overutilizing the CPU.

bash sar 1 5

  • Analyzing Disk I/O Performance: If your system is experiencing slow disk performance, use sar -d to monitor disk I/O and identify potential bottlenecks.

bash sar -d 1 5

  • Historical Performance Analysis: sar can be configured to collect system performance data over time, which can then be analyzed to identify trends or issues that develop gradually.

For example, to view historical CPU usage from the sar logs:

bash sar -f /var/log/sa/sa10

Here, /var/log/sa/sa10 refers to a sar log file for a specific day.

Conclusion

The sar command is a versatile and powerful tool for system performance monitoring in Linux. Whether you're interested in real-time performance data or historical analysis, sar provides detailed insights into CPU, disk, and other system activities. For more in-depth usage and advanced options, refer to the man sar page or explore additional resources like the linked sar guide.