2.5.4.4. The sar command
The
sar command produces system utilization reports based on the data collected by sadc. As configured in Red Hat Enterprise Linux, sar is automatically run to process the files automatically collected by sadc. The report files are written to /var/log/sa/ and are named sar<dd>, where <dd> is the two-digit representations of the previous day's two-digit date.
sar is normally run by the sa2 script. This script is periodically invoked by cron via the file sysstat, which is located in /etc/cron.d/. By default, cron runs sa2 once a day at 23:53, allowing it to produce a report for the entire day's data.
2.5.4.4.1. Reading sar Reports
The format of a
sar report produced by the default Red Hat Enterprise Linux configuration consists of multiple sections, with each section containing a specific type of data, ordered by the time of day that the data was collected. Since sadc is configured to perform a one-second measurement interval every ten minutes, the default sar reports contain data in ten-minute increments, from 00:00 to 23:50[7].
Each section of the report starts with a heading describing the data contained in the section. The heading is repeated at regular intervals throughout the section, making it easier to interpret the data while paging through the report. Each section ends with a line containing the average of the data reported in that section.
Here is a sample section
sar report, with the data from 00:30 through 23:40 removed to save space:
00:00:01 CPU %user %nice %system %idle 00:10:00 all 6.39 1.96 0.66 90.98 00:20:01 all 1.61 3.16 1.09 94.14 … 23:50:01 all 44.07 0.02 0.77 55.14 Average: all 5.80 4.99 2.87 86.34
In this section, CPU utilization information is displayed. This is very similar to the data displayed by
iostat.
Other sections may have more than one line's worth of data per time, as shown by this section generated from CPU utilization data collected on a dual-processor system:
00:00:01 CPU %user %nice %system %idle 00:10:00 0 4.19 1.75 0.70 93.37 00:10:00 1 8.59 2.18 0.63 88.60 00:20:01 0 1.87 3.21 1.14 93.78 00:20:01 1 1.35 3.12 1.04 94.49 … 23:50:01 0 42.84 0.03 0.80 56.33 23:50:01 1 45.29 0.01 0.74 53.95 Average: 0 6.00 5.01 2.74 86.25 Average: 1 5.61 4.97 2.99 86.43
There are a total of seventeen different sections present in reports generated by the default Red Hat Enterprise Linux
sar configuration; some are explored in upcoming chapters. For more information about the data contained in each section, refer to the sar(1) man page.
[7]
Due to changing system loads, the actual time at which the data was collected may vary by a second or two.
