sar

Understanding sar’s Functionality

sar gathers system performance data from various sources, including the kernel’s accounting mechanisms. It can report on CPU utilization, memory usage, I/O activity, network traffic, and much more. The beauty of sar lies in its ability to collect data over time, allowing you to analyze trends and identify patterns. This historical perspective is important for accurate performance diagnosis.

Installing sar

sar is typically part of the sysstat package. If you don’t have it installed, use your distribution’s package manager:

• Debian/Ubuntu: sudo apt-get update && sudo apt-get install sysstat
• Red Hat/CentOS/Fedora: sudo yum update && sudo yum install sysstat

Basic sar Usage: CPU Utilization

Let’s start with a fundamental example: monitoring CPU usage. The following command displays CPU utilization statistics for the last 10 minutes, with a 1-minute interval:

sar -u 1 10

This command breaks down as follows:

• sar: The System Activity Reporter command.
• -u: Specifies that we want CPU utilization statistics.
• 1: Indicates a sampling interval of 1 minute.
• 10: Specifies that we want data for the last 10 minutes.

The output will show utilization percentages for various CPU cores (if your system has multiple cores) along with the average. You’ll see metrics like %usr (user CPU time), %sys (system CPU time), %idle (idle CPU time), and more.

Advanced sar Usage: Memory Statistics

To examine memory usage, we use the -r option:

sar -r 1 10

This command will show memory statistics including:

• kbmemfree: The amount of free memory.
• kbmemused: The amount of used memory.
• kbbuffers: Memory used for buffering I/O operations.
• kbcached: Memory used for caching.

Analyzing I/O Performance

Monitoring I/O operations is vital for identifying disk bottlenecks. Use the -b option:

sar -b 1 10

This will display statistics related to block device activity, including:

• tps: Transactions per second.
• rkB/s: Read kilobytes per second.
• wkB/s: Write kilobytes per second.
• avgrq-sz: Average request size.

Long-Term Monitoring with Log Files

sar can write its output to a log file for later analysis. This is essential for tracking performance trends over extended periods. To do this, use the -f option to specify a log file (or let sar create one):

sar -u 1 60 > cpu_usage.log

This command saves CPU utilization data for the last 60 minutes (1-minute intervals) to a file named cpu_usage.log. You can then analyze this log file at any time.

sar -f cpu_usage.log

This will display the data stored in cpu_usage.log. You can further filter and analyze the data using tools like awk, grep, and sed.

More options:

The sar command has numerous other options for detailed analysis of various system aspects, including network statistics (-n), paging statistics (-W), and more. Consult the man sar page for a complete list of options and detailed explanations. Experiment with different options and find the ones most relevant to your performance analysis needs.