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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 realtime cpuusage in output. Please help me to improve my command.
You're right, top appears to give incorrect CPU usage on first iteration. You can work around this issue like this:
top -b -n2 | grep "Cpu(s)"|tail -n 1 | awk '{print $2 + $4}'
This will of course take twice as much time, but it will work anyway.
If you still want it work faster, you can use -d option, e.g. for 1-second total period of measurement use half of it:
top -d 0.5 -b -n2 | grep "Cpu(s)"|tail -n 1 | awk '{print $2 + $4}'
Technically the first top doesn't always output the same value; it just outputs the average CPU load since last boot. Because top uses the delta of /proc/stat stats to calculate the CPU load, the first value is calculated while comparing against zero, yielding incorrect (but WAD) result.
If you don't want to use top, you can directly parse /proc/stat:
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) "%"}'
It's also faster and more accurate this way.
You can test it with stress:
stress -c 1 -q &
And do
killall stress
after.
watch can be run on it: watch -n1 "bash ./cpu"
– Brent Faust
May 21 '15 at 5:31
/proc/stat is pretty cool but it appear to have the same drawback as top's first iteration: It outputs the average CPU load since last boot, not the current one.
– pieroxy
Feb 28 '16 at 23:01
Just to expand on @Ruslan's answer, top splits CPU usage between user, system processes and nice processes, we want the sum of the three. So, we can run top in batch mode which allows us to parse its output. However, 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 -bn 2 -d 0.01 | grep '^%Cpu' | tail -n 1 | gawk '{print $2+$4+$6}'
Maybe use this one based on ps output :
ps aux | awk 'BEGIN { sum = 0 } { sum += $3 }; END { print sum }
Use watch command or for loop in shell,
i.e watch -n1 "top -b -n1 | grep 'Cpu(s)' | awk '{print \$2 + \$4}'"
Why do you care about the CPU usage? The load average is a much better indicator:
cat /proc/loadavg
If you really need the CPU usage, parsing /proc/stat is probably the way to go.
/proc/stat doesn't give CPU usage as it is, one has to read it twice with some time between reads and do some calculations to get CPU usage. This is just what top does.
– Ruslan
Sep 17 '13 at 11:41
Using sar command
sar 1 10
That means: get 10 times result in every second
time. On my system it only takes 0.165s. – depquid Mar 26 '13 at 18:16time (top -b -n1 | grep "Cpu(s)" | awk '{print $2 + $4}' )– depquid Mar 28 '13 at 20:59