How to discover number of *logical* cores on Mac O

Question

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.

Answer 1

CLARIFICATION

When this question was asked the OP did not say that he wanted the number of LOGICAL cores rather than the actual number of cores, so this answer logically (no pun intended) answers with a way to get the actual number of real physical cores, not the number that the OS tries to virtualize through hyperthreading voodoo.

UPDATE TO HANDLE FLAW IN YOSEMITE

Due to a weird bug in OS X Yosemite (and possibly newer versions, such as the upcoming El Capitan), I've made a small modification. (The old version still worked perfectly well if you just ignore STDERR, which is all the modification does for you.)

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Every other answer given here either

1. gives incorrect information
2. gives no information, due to an error in the command implementation
3. runs unbelievably slowly (taking the better part of a minute to complete), or
4. gives too much data, and thus might be useful for interactive use, but is useless if you want to use the data programmatically (for instance, as input to a command like bundle install --jobs 3 where you want the number in place of 3 to be one less than the number of cores you've got, or at least not more than the number of cores)

The way to get just the number of cores, reliably, correctly, reasonably quickly, and without extra information or even extra characters around the answer, is this:

system_profiler SPHardwareDataType 2> /dev/null | grep 'Total Number of Cores' | cut -d: -f2 | tr -d ' '

Answer 2

As jkp said in a comment, that doesn't show the actual number of physical cores. to get the number of physical cores you can use the following command:

system_profiler SPHardwareDataType

Answer 3

$ system_profiler | grep 'Total Number Of Cores'

Answer 4

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.

Answer 5

To do this in C you can use the sysctl(3) family of functions:

int count;
size_t count_len = sizeof(count);
sysctlbyname("hw.logicalcpu", &count, &count_len, NULL, 0);
fprintf(stderr,"you have %i cpu cores", count);

Interesting values to use in place of "hw.logicalcpu", which counts cores, are:

hw.physicalcpu - The number of physical processors available in the current power management mode.

hw.physicalcpu_max - The maximum number of physical processors that could be available this boot.

hw.logicalcpu - The number of logical processors available in the current power management mode.

hw.logicalcpu_max - The maximum number of logical processors that could be available this boot.

Answer 6

On a MacBook Pro running Mavericks, sysctl -a | grep hw.cpu will only return some cryptic details. Much more detailed and accessible information is revealed in the machdep.cpu section, ie:

sysctl -a | grep machdep.cpu

In particular, for processors with HyperThreading (HT), you'll see the total enumerated CPU count (logical_per_package) as double that of the physical core count (cores_per_package).

sysctl -a | grep machdep.cpu  | grep per_package