Is it possible to get current CPU utilisation from a specific core via /sys in Linux?

I would like to write a shellscript that reads the current CPU utilisation on a per-core basis. Is it possible to read this from the /sys directory in Linux (CentOS 8)? I have found /sys/bus/cpu/drivers/processor/cpu0 which does give me a fair bit of information (like current frequency), but I’ve yet to figure out how to read CPU utilisation.

In other words: Is there a file that gives me current utilisation of a specific CPU core in Linux, specifically CentOS 8?

Answer

I believe that you should be able to extract information from /proc/stat – the lines that start with cpu$N, where $N is 0, 1, 2, …… For example:

Strongly suggesting reading articles referenced on other answer.

cpu0 101840 1 92875 80508446 4038 0 4562 0 0 0
cpu1 81264 0 68829 80842548 4424 0 2902 0 0 0

Repeated call will show larger values:

cpu  183357 1 162020 161382289 8463 0 7470 0 0 0
cpu0 102003 1 93061 80523961 4038 0 4565 0 0 0
cpu1 81354 0 68958 80858328 4424 0 2905 0 0 0

Notice CPU0 5th column (idle count) moving from 80508446 to 80523961

Format of each line in

cpuN user-time nice-time system-time idle-time io-wait ireq softirq steal guest guest_nice

So a basic solution:

while true ;

   for each cpu
       read current counters, at least user-time system-time and idle 
       usage = current(user-time + system-time) - prev(user-time+system-time)
       idle = current(idle) - prev(idle)
       utilization = usage/(usage+idle)
       // print or whatever.
       set prev=current
done