[macos] How to discover number of *logical* cores on Mac OS X?


Even easier:

sysctl -n hw.ncpu

How can you tell, from the command line, how many cores are on the machine when you're running Mac OS X? On Linux, I use:

x=$(awk '/^processor/ {++n} END {print n+1}' /proc/cpuinfo)

It's not perfect, but it's close. This is intended to get fed to make, which is why it gives a result 1 higher than the actual number. And I know the above code can be written denser in Perl or can be written using grep, wc, and cut, but I decided the above was a good tradeoff between conciseness and readability.

VERY LATE EDIT: Just to clarify: I'm asking how many logical cores are available, because this corresponds with how many simultaneous jobs I want make to spawn. jkp's answer, further refined by Chris Lloyd, was exactly what I needed. YMMV.

system_profiler SPHardwareDataType shows I have 1 processor and 4 cores.

[~] system_profiler SPHardwareDataType Hardware:

Hardware Overview:

  Model Name: MacBook Pro
  Model Identifier: MacBookPro9,1
  Processor Name: Intel Core i7
  Processor Speed: 2.6 GHz
  Number of Processors: 1
  Total Number of Cores: 4



However, sysctl disagrees:

[~] sysctl -n hw.logicalcpu 8 [~] sysctl -n hw.physicalcpu 4 [~]

But sysctl appears correct, as when I run a program that should take up all CPU slots, I see this program taking close to 800% of CPU time (in top):

4306 top 5.6
4304 java 745.7 4296 locationd 0.0

This should be cross platform. At least for Linux and Mac OS X.

python -c 'import multiprocessing as mp; print(mp.cpu_count())'

A little bit slow but works.

Comments for 2 good replies above:

1) re the accepted reply (and comments) by jkp: hw.ncpu is apparently deprecated in favor of hw.logicalcpu (https://ghc.haskell.org/trac/ghc/ticket/8594)

2) re the 2014 update by Karl Ehr: on my computer (with 2.5 ghz intel core i7),sysctl -a | grep machdep.cpu | grep per_package returns different numbers:

machdep.cpu.logical_per_package: 16

machdep.cpu.cores_per_package: 8

The desired values are:

machdep.cpu.core_count: 4

machdep.cpu.thread_count: 8

Which match:

hw.physicalcpu: 4

hw.logicalcpu: 8

The following command gives you all information about your CPU

$ sysctl -a | sort | grep cpu

Use the system_profiler | grep "Cores" command.

I have a:

MacBook Pro Retina, Mid 2012.

Processor: 2.6 GHz Intel Core i7

user$ system_profiler | grep "Cores"
      Total Number of Cores: 4

user$ sysctl -n hw.ncpu

According to Wikipedia, (http://en.wikipedia.org/wiki/Intel_Core#Core_i7) there is no Core i7 with 8 physical cores so the Hyperthreading idea must be the case. Ignore sysctl and use the system_profiler value for accuracy. The real question is whether or not you can efficiently run applications with 4 cores (long compile jobs?) without interrupting other processes.

Running a compiler parallelized with 4 cores doesn't appear to dramatically affect regular OS operations. So perhaps treating it as 8 cores is not so bad.