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When running top -b -n 1, the command always returns the same CPU values. Consider the following test run 5 times in succession:
[user@server ~]$ top -b -n 5 -d.2 | grep "Cpu(s)"
Cpu(s): 18.5%us, 10.0%sy, 0.0%ni, 67.0%id, 4.2%wa, 0.0%hi, 0.2%si, 0.1%st
Cpu(s): 39.8%us, 27.7%sy, 0.0%ni, 31.3%id, 0.0%wa, 0.0%hi, 1.2%si, 0.0%st
Cpu(s): 39.0%us, 35.4%sy, 0.0%ni, 23.2%id, 0.0%wa, 0.0%hi, 1.2%si, 1.2%st
Cpu(s): 41.2%us, 34.1%sy, 0.0%ni, 15.3%id, 1.2%wa, 0.0%hi, 2.4%si, 5.9%st
Cpu(s): 59.0%us, 30.1%sy, 0.0%ni, 4.8%id, 0.0%wa, 0.0%hi, 3.6%si, 2.4%st
[user@server ~]$ top -b -n 5 -d.2 | grep "Cpu(s)"
Cpu(s): 18.5%us, 10.0%sy, 0.0%ni, 67.0%id, 4.2%wa, 0.0%hi, 0.2%si, 0.1%st
Cpu(s): 18.9%us, 17.8%sy, 0.0%ni, 63.3%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu(s): 18.8%us, 21.2%sy, 0.0%ni, 55.3%id, 2.4%wa, 0.0%hi, 1.2%si, 1.2%st
Cpu(s): 29.4%us, 24.7%sy, 0.0%ni, 45.9%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu(s): 60.5%us, 24.4%sy, 0.0%ni, 11.6%id, 1.2%wa, 0.0%hi, 1.2%si, 1.2%st
[user@server ~]$ top -b -n 5 -d.2 | grep "Cpu(s)"
Cpu(s): 18.5%us, 10.0%sy, 0.0%ni, 67.0%id, 4.2%wa, 0.0%hi, 0.2%si, 0.1%st
Cpu(s): 43.4%us, 38.6%sy, 0.0%ni, 15.7%id, 0.0%wa, 0.0%hi, 1.2%si, 1.2%st
Cpu(s): 55.3%us, 40.0%sy, 0.0%ni, 4.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu(s): 39.5%us, 48.8%sy, 0.0%ni, 5.8%id, 1.2%wa, 0.0%hi, 1.2%si, 3.5%st
Cpu(s): 40.7%us, 55.6%sy, 0.0%ni, 2.5%id, 0.0%wa, 0.0%hi, 0.0%si, 1.2%st
[user@server ~]$ top -b -n 5 -d.2 | grep "Cpu(s)"
Cpu(s): 18.5%us, 10.0%sy, 0.0%ni, 67.0%id, 4.2%wa, 0.0%hi, 0.2%si, 0.1%st
Cpu(s): 27.1%us, 10.6%sy, 0.0%ni, 61.2%id, 1.2%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu(s): 25.3%us, 5.7%sy, 0.0%ni, 67.8%id, 0.0%wa, 0.0%hi, 0.0%si, 1.1%st
Cpu(s): 15.5%us, 16.7%sy, 0.0%ni, 64.3%id, 0.0%wa, 0.0%hi, 0.0%si, 3.6%st
Cpu(s): 57.3%us, 11.2%sy, 0.0%ni, 30.3%id, 0.0%wa, 0.0%hi, 0.0%si, 1.1%st
[user@server ~]$ top -b -n 5 -d.2 | grep "Cpu(s)"
Cpu(s): 18.5%us, 10.0%sy, 0.0%ni, 67.0%id, 4.2%wa, 0.0%hi, 0.2%si, 0.1%st
Cpu(s): 44.0%us, 6.0%sy, 0.0%ni, 42.9%id, 0.0%wa, 0.0%hi, 3.6%si, 3.6%st
Cpu(s): 45.8%us, 9.6%sy, 0.0%ni, 44.6%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu(s): 34.5%us, 8.3%sy, 0.0%ni, 57.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu(s): 38.6%us, 14.5%sy, 0.0%ni, 45.8%id, 0.0%wa, 0.0%hi, 0.0%si, 1.2%st
Any idea what could be the issue here?
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The top (table of processes) command shows a real-time view of running processes in Linux and displays kernel-managed tasks. The command also provides a system information summary that shows resource utilization, including CPU and memory usage. In this tutorial, you will learn to use the top command in Linux.
The top command (table of processes) displays the processor activity of your Linux box and also displays tasks managed by the kernel in real-time. It also shows information about CPU and memory utilization of a list of running processes.
However, besides real time viewing of the running system, top command output can be saved to a file, by using the -b flag, which instructs top to operate in batch mode and -n flag to specify the amount of iteration the command should output.
Typing h invokes the "help" screen, which also shows the default delay (the time between screen updates). By default, this value is (around) three seconds, but you can change it by typing d (presumably for "delay") or s (probably for "screen" or "seconds").
CPU utilisation figures are calculated as an average over a time interval. For the first iteration, that time interval is "from system boot until now"; for subsequent iterations, the time interval is "from the last iteration until now".
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