Generate CPU, Memory and I/O Report using SAR command

SAR stands for System Activity Report, as its name suggest, sar command is used to collect, report & save CPU, Memory, I/O usage in Unix like operating systems. SAR command generate the reports on the fly and can also save the reports in log files as well.

In this article we will discuss different examples of sar command on RHEL 8/ RHEL 9 & Ubuntu 22.04. In case,  sar is not installed on your system then use beneath steps,

 Install SAR on RHEL 8 / RHEL 9

$ sudo dnf install sysstat -y

Install SAR on Ubuntu 22.04 / 20.04

$ sudo apt update $ sudo apt install -y sysstat

Start the sadc (system activity data collector) service(sysstat) so that it saves the reports in log file “/var/log/sa/saDD”  where DD represents Current day and already existing files will be archived.

$ systemctl start sysstat
$ systemctl enable sysstat

Once the sysstat service started then sar will start  collecting the data every 10 minutes and generate its report daily. On RHEL 8/ RHEL 9, following systemd file is responsible for collecting and generating reports.

$ systemctl cat sysstat-collect.timer

On Ubuntu 22.04/20.04, following cron tab is responsible for generating the report every 10 minutes.

$ cat /etc/cron.d/sysstat

Below is the default config file of sysstat (sar command) on RHEL systems.

$ cat /etc/sysconfig/sysstat

Default Configuartion of sysstat on Ubuntu 22.04/20.04

$ cat /etc/default/sysstat

Without any further delay, let’s deep dive into examples of sar command and see how the reports are generated.

1) Generating CPU Report on the Fly 5 times every 2 seconds

To generate the CPU report 5 times every 2 seconds, run

$ sar 2 5

If the %I/O wait is more than zero for a longer period of time then we can consider there is some bottleneck in I/O system (Hard disk or Network )

2) Saving sar command output to a file

To save the sar command output to a file, use -o option, example is shown below

$ sar 2 5 -o /tmp/data > /dev/null 2>&1

Now use “sar -f <file-name>” to display the reports.

$ sar -f /tmp/data

3) Generating Memory Usage Report

-r option in the sar command is used to generate memory usage report.

[root@localhost ~]# sar -r 2 5

kbcommit & %commit is the overall memory used including RAM & Swap

4) Generating Paging Statistics Report

-B option in the sar command is used to display paging statistics. Example is shown below,

[root@localhost ~]# sar -B 2 5

In the report majflts/s shows the major faults per second means number of pages loaded into the memory from disk (swap), if its value is higher then we can say that system is running out of RAM.

%vmeff indicates the number of pages scanned per second, if it’s vaule is 100 % its is consider OK and when it is below 30 % then there is some issue with virtual memory. Zero value indicates that there is no page scanned during that time.

5) Generating Block Device Statistics Report

-d option in the sar command is used to display the block device statistics report. Using option -p (pretty-print) along with -d make the dev column more readable, example is shown below :

[root@localhost ~]# sar -d -p 2 4

6) Generating Network Statistic Report

-n option in the sar command is used to generate network statistic report. Below is the synatx :

$ sar -n {keyword} or {ALL}

Following keywords can be used : DEV, EDEV, NFS, NFSD, SOCK, IP, EIP, ICMP, EICMP, TCP, ETCP, UDP, SOCK6, IP6, EIP6, ICMP6, EICMP6 & UDP6.

To generate all network statistic report run following command :

$ sar -n ALL

7) Reading SAR Log File using -f

As we have stated above that sar logs files are kept under /var/log/sa/saDD, using -f option in sar command we can read these log files. One example is shown below,

$ sar -r -f /var/log/sa/sa16

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