Comments on How to Monitor a System with Sysstat on Centos

Hi,

 I don't think you need to create cronjobs, as they are created automatically at the install of the package.

 Good article, though!

Yep, that was in there, just tucked away:

>By creating a file called sysstat in /etc/cron.d, we can tell cron to run sar every day.
>Fortunately, the Systat package that yum installed already did this step for us.

Timothy Doyle

CEO

Quantact Hosting Solutions, Inc.

http://www.quantact.com 

Normally I have this in my cronjob:
0 23 * * * /usr/bin/sar -q -r | /bin/mail -s "$HOSTNAME Daily_Sar_Report" [email protected]

This is a particularly good monitoring tool to install. Let it run for at least a full day, and at the end of a day, run sar -A | less You will be amazed at how many system resources are being monitored. Also, it is an "old school" tool from the commercial UNIX world, and has earned the respect of many gray-bearded admins. Finally, O'Reilly's "Swordfish book", System Performance Tuning, gives a great explanation on what useful data you can get from sar, and what it is trying to tell you about the system health. The book is a bit dated now, but there's still plenty of great stuff in there. Nice to see someone pushing this tool, as it is usually one of the first packages I install after a clean build. Also check out http://www-128.ibm.com/developerworks/eserver/library/es-unix-perfmonsar.html

Thank you for the article. I learned a lot.

you may monitor all these data and even more with dim_STAT tool (http://dimitrik.free.fr), as well analyze several hosts on the same time, produce professional reports, etc. This tool is free and run on most of distro...
-sys

In the crontab entry, you should not be limiting the interval to 1 second. Sar uses the same system resources no matter how long the interval is. It reads kernel values, sleeps, reads the values again and records/prints the difference value. 1 second, 10 seconds, 1200 seconds are the same as far as sar’s resource usage. 99.99% of sar’s usage is sleep, which is what the kernel does anyway when it’s not doing anything. Note below that the first sar sample of only a second showed an average cpu of 3%. The longer samples, averaging over a longer period, show that 6% is probably more of an accurate average, at this time. The web pages I’ve seen so far feed each other with this 1 second sample thing, almost like someone is afraid sar might bog the system down. It won’t. The same two sets of kernel reads happens no matter what the interval is:<br><br>

time sar 1 1; time sar 10 1; time sar 100 1<br>
Linux 2.6.18-194.el5 (blahblah) 10/07/14<br><br>

12:04:51 CPU %user %nice %system %iowait %steal %idle<br>
12:04:52 all 3.00 0.00 0.75 0.00 0.00 96.25<br>
Average: all 3.00 0.00 0.75 0.00 0.00 96.25<br>
sar 1 1 0.00s user 0.00s system 0% cpu 1.005 total<br>
Linux 2.6.18-194.el5 (blahblah) 10/07/14<br><br>

12:04:52 CPU %user %nice %system %iowait %steal %idle<br>
12:05:02 all 6.21 0.00 0.93 0.20 0.00 92.67<br>
Average: all 6.21 0.00 0.93 0.20 0.00 92.67<br>
sar 10 1 0.00s user 0.00s system 0% cpu 10.005 total<br>
Linux 2.6.18-194.el5 (blahblah) 10/07/14<br><br>

12:05:02 CPU %user %nice %system %iowait %steal %idle<br>
12:06:42 all 6.32 0.00 0.97 0.24 0.00 92.47<br>
Average: all 6.32 0.00 0.97 0.24 0.00 92.47<br>
sar 100 1 0.00s user 0.00s system 0% cpu 1:40.01 total<br><br>

From the man page example it shows each hour having 3 20 minute samples. This provides accurate averaging and small sa## files. A 1 second interval each 10 minutes is 1/600th of the information available.<br><br>

EXAMPLES<br>
To create a daily record of sar activities, place the following entry in your root or adm crontab file:<br>

0 8-18 * * 1-5 /usr/lib/sa/sa1 1200 3 &

Thanks!

12:00:01 AM   runq-sz  plist-sz   ldavg-1   ldavg-5  ldavg-15   blocked

Average:            1       780      0.23      0.23      0.23         0