26

Chapter 2. Resource Monitoring

2.5.4.4. The

sar

command

The

sar

command produces system utilization reports based on the data collected by

sadc

. As con 

figured in Red Hat 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

sys 

stat

, which is located in

/etc/crond.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 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

4

.

Each section of the report starts with a heading that illustrates 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 gener 

ated 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

Linux

sar

configuration; many are discussing in upcoming chapters. For more information about the

data contained in each section, see the

sar(1)

man page.

4. Due to changing system loads, the actual time that the data was collected may vary by a second or two.