sar Command: Tutorial & Examples

Monitoring performance

The sar command, also known as the System Activity Reporter, is an incredibly useful tool when it comes to monitoring the performance of a Linux server. It comes from the sysstat package and provides a comprehensive view of your system's activity. It works by collecting, reporting, and saving system activity information for later analysis.

Understanding sar is crucial for server administrators because it helps to identify any potential high load issues and allows them to tune their servers accordingly for optimal performance.

How Does sar Work?

The sar command collects and displays data by reading binary data files in the /var/log/sa directory. These files are created by the sadc (system activity data collector) utility, which is a part of the sysstat package.

The data collected includes CPU activity, memory/paging, interrupts, device load, network and more. The command is typically used in combination with cron jobs to gather data throughout the day.

Typical Problems Solved by sar

The sar command can help solve a variety of performance-related issues on a Linux server. For instance, it can be used to identify high CPU usage over time, observe trends in memory usage, or diagnose disk I/O bottlenecks. An administrator can then use this data to optimize server performance and troubleshoot issues such as slow servers or system crashes.

Examples of Using sar Command

Here are a few examples of how you can use the sar command:

1. Display CPU Usage

To display the CPU usage, you can use the sar command followed by the interval and the number of times you want the data to be updated. For instance, if you want to display CPU usage every 2 seconds for a total of 3 times, the command would be:

sar 2 3

The output might look something like this:

Linux 4.15.0-54-generic (ubuntu)    Thursday 13 June 2019   _x86_64_    (2 CPU)

10:51:51        CPU     %user     %nice   %system   %iowait    %steal     %idle
10:51:53        all      0.50      0.00      0.50      0.00      0.00     99.00
10:51:55        all      0.50      0.00      0.50      0.00      0.00     99.00
Average:        all      0.50      0.00      0.50      0.00      0.00     99.00

2. Display Memory Usage

To display memory usage, you can use the -r option. For instance:

sar -r 2 3

The output might look like this:

10:51:51 kbmemfree kbmemused  %memused kbbuffers  kbcached  kbcommit   %commit  kbactive   kbinact
10:51:53   1023840   3004172     74.57    123440   2518752     23060      0.56   1620016   1141204
10:51:55   1023840   3004172     74.57    123440   2518752     23060      0.56   1620016   1141204
Average:   1023840   3004172     74.57    123440   2518752     23060      0.56   1620016   1141204

Conclusion

The sar command is a powerful tool for monitoring system performance and diagnosing issues in a Linux server environment. By understanding how to use it effectively, you can ensure your server is running optimally and troubleshoot any issues that may arise.