I am using sar utility for collecting and saving system activity information. After saving the information, I am seeing/reporting the information but the output is not matching. Can some one please help me in understanding the behavior or if I am doing a silly mistake in my understanding. Below are the details.
Step 1: To collect and save system activity
sar -o sa_30_dec_2012 1 > /dev/null 2>&1 &
Step 2: To report first 10 minutes readings with an interval of 1 second
sar 1 10 -f sa_30_dec_2012
Step 3: To report first 10 readings within an interval of 2 seconds
sar 2 5 -f sa_30_dec_2012
Output of Step 2
07:18:34 IST CPU %user %nice %system %iowait %steal %idle
07:18:35 IST all 1.51 0.00 1.51 3.02 0.00 93.97
07:18:36 IST all 1.50 0.00 1.00 0.00 0.00 97.50
07:18:37 IST all 1.02 0.00 0.51 0.00 0.00 98.48
07:18:38 IST all 2.55 0.00 0.51 0.00 0.00 96.94
07:18:39 IST all 3.03 0.00 0.51 0.00 0.00 96.46
07:18:40 IST all 1.49 0.00 1.49 3.48 0.00 93.53
07:18:41 IST all 1.52 0.00 0.51 0.00 0.00 97.97
07:18:42 IST all 1.01 0.00 1.01 0.00 0.00 97.99
07:18:43 IST all 1.53 0.00 0.00 0.00 0.00 98.47
07:18:44 IST all 2.53 0.00 1.52 0.00 0.00 95.96
Average: all 1.77 0.00 0.86 0.66 0.00 96.72
Output of Step 3
07:18:34 IST CPU %user %nice %system %iowait %steal %idle
07:18:36 IST all 1.50 0.00 1.25 1.50 0.00 95.74
07:18:38 IST all 1.78 0.00 0.51 0.00 0.00 97.71
07:18:40 IST all 2.26 0.00 1.00 1.75 0.00 94.99
07:18:42 IST all 1.26 0.00 0.76 0.00 0.00 97.98
07:18:44 IST all 2.03 0.00 0.76 0.00 0.00 97.21
Average: all 1.77 0.00 0.86 0.66 0.00 96.72
If you observe, the readings for timestamp 07:18:36 match but the readings after that do not match (the values are not equal). For example, the values of the following timestamps are not equal:-
Step 2 output
07:18:38 IST all 2.55 0.00 0.51 0.00 0.00 96.94
07:18:40 IST all 1.49 0.00 1.49 3.48 0.00 93.53
Step 3 output
07:18:38 IST all 1.78 0.00 0.51 0.00 0.00 97.71
07:18:40 IST all 2.26 0.00 1.00 1.75 0.00 94.99
Why are the Step 2 and Step 3 outputs not matching?
These commands were executed on Ubuntu 12.04 LTS.
Any help is very much appreciated.