Sometimes you need to determine how many CPU cores a system has. This might be when you’re running make to use some or all of your CPU cores or some compression tools that take a CPU cores argument.
If you’re not trying to find this number in a script you can grep the contents of /proc/cpuinfo:
cat /proc/cpuinfo | grep processor
processor : 0
processor : 1
processor : 2
processor : 3
processor : 4
processor : 5
processor : 6
processor : 7
Or you could open top and press 1 which will list all your CPU cores individually:
top - 12:56:04 up 3:04, 1 user, load average: 0.58, 0.41, 0.38
Tasks: 231 total, 1 running, 230 sleeping, 0 stopped, 0 zombie
%Cpu0 : 0.7 us, 0.0 sy, 0.0 ni, 99.3 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu1 : 0.7 us, 0.7 sy, 0.0 ni, 98.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu2 : 0.7 us, 1.3 sy, 0.0 ni, 98.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu3 : 6.5 us, 1.3 sy, 0.0 ni, 92.2 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu4 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu5 : 4.3 us, 4.9 sy, 0.0 ni, 90.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu6 : 0.7 us, 1.3 sy, 0.0 ni, 98.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu7 : 0.7 us, 2.0 sy, 0.0 ni, 97.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
GiB Mem : 15.1 total, 8.3 free, 2.6 used, 4.2 buff/cache
GiB Swap: 0.2 total, 0.2 free, 0.0 used. 10.6 avail Mem
Both of these solutions are a difficult to use in a script. If you need that information in an automated way just use nproc. When you run nproc it will output the number of CPU cores and nothing else:
$ nproc
8
If you need to get CPU cores minus N cores pass the --ignore=N flag:
$ nproc --ignore=1
7
You don’t need to employ grep or any other text manipulation or math tools to get the number you need.