Ubuntu: Getting cpu usage realtime



Question:

When I execute following command to get cpu usage , I get nice + user cpu usage.

top -b -n1 | grep "Cpu(s)" | awk '{print $2 + $4}'   

Output:

14.5  

Here I am getting problem is that the output depends on top command thus it doesn't change instantly as top command. So I am not getting correct cpu instantly. It gives same output and not changing.

I want to get real-time cpu usage in output. Please help me to improve my command.


Solution:1

If you can afford a delay of one second, this will print CPU usage as a simple percentage:

echo $[100-$(vmstat 1 2|tail -1|awk '{print $15}')]  

(Without the one-second delay, vmstat can only print average values since boot.)


Solution:2

This is a known issue with top. As explained here, the 1st iteration of top -b returns the percentages since boot, we therefore need at least two iterations (-n 2) to get the current percentage. To speed things up, you can set the delay between iterations to 0.01. top splits CPU usage between user, system processes and nice processes, we want the sum of the three. Finally, you grep the line containing the CPU percentages and then use gawk to sum user, system and nice processes:

    top -bn 2 -d 0.01 | grep '^%Cpu' | tail -n 1 | gawk '{print $2+$4+$6}'          -----  ------   -----------    ---------   ----------------------            |      |           |             |             |------> add the values            |      |           |             |--> keep only the 2nd iteration            |      |           |----------------> keep only the CPU use lines            |      |----------------------------> set the delay between runs            |-----------------------------------> run twice in batch mode  


Solution:3

I have tried several ways, but this seems to me the most accurate:

cat <(grep 'cpu ' /proc/stat) <(sleep 1 && grep 'cpu ' /proc/stat) | awk -v RS="" '{print ($13-$2+$15-$4)*100/($13-$2+$15-$4+$16-$5)}'  

Got it from here


Solution:4

Use -n2. This will output two lines. The 1st time top prints the line does not qualify for the state at that point in time. Then adjust your script to ignore the first line.


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