Chapter 2. Resource Monitoring

25

The device specification, displayed as

dev major number  sequence number

, where

major number

is the device's major number

3

, and

sequence number

is a sequence

number starting at zero.

The number of transfers (or I/O operations) per second.

The number of 512 byte blocks read per second.

The number of 512 byte blocks written per second.

The total number of 512 byte blocks read.

The total number of 512 byte block written.

This is just a sample of the information that can be obtained using

iostat

. For more information, see

the

iostat(1)

man page.

2.5.4.2. The

mpstat

command

The

mpstat

command at first appears no different from the CPU utilization report produced by

io 

stat

:

Linux 2.4.18 14smp (pigdog.example.com)

12/11/2002

07:09:26 PM

CPU

%user

%nice %system

%idle

intr/s

07:09:26 PM

all

6.40

5.84

3.29

84.47

542.47

With the exception of an additional column showing the interrupts per second being handled by the

CPU, there is no real difference. However, the situation changes if

mpstat

's

 P ALL

option is used:

Linux 2.4.18 14smp (pigdog.example.com)

12/11/2002

07:13:03 PM

CPU

%user

%nice %system

%idle

intr/s

07:13:03 PM

all

6.40

5.84

3.29

84.47

542.47

07:13:03 PM

0

6.36

5.80

3.29

84.54

542.47

07:13:03 PM

1

6.43

5.87

3.29

84.40

542.47

On multiprocessor systems,

mpstat

allows the utilization for each CPU to be viewed individually,

making it possible to determine how effectively each CPU is being used.

2.5.4.3. The

sadc

command

As stated earlier, the

sadc

command collects system utilization data and writes it to a file for later

analysis. By default, the data is written to files in the

/var/log/sa/

directory. The files are named

sa dd

, where

dd

is the current day's two digit date.

sadc

is normally run by the

sa1

script. This script is periodically invoked by

cron

via the file

sys 

stat

, which is located in

/etc/crond.d

. The

sa1

script invokes

sadc

for a single one second

measuring interval. By default,

cron

runs

sa1

every 10 minutes, adding the data collected during

each interval to the current

/var/log/sa/sa dd

file.

3. Device major numbers can be found by using ls  l to display the desired device file in /dev/. Here is

sample output from ls  l /dev/hda:

brw rw    

1 root

disk

3,

0 Aug 30 19:31 /dev/hda

The major number in this example is 3, and appears between the file's group and its minor number.