Number of CPU cores on Linux and OS X

sysctl -n hw.ncpu: OS X

I can see the number of cores or the number of threads.

sysctl -n hw.ncpu
8

sysctl -n hw.physicalcpu
4

sysctl -n hw.logicalcpu
8

nproc: Raspberry Pi & Linux

On a Raspberry Pi 2 I can see that I have 4 cores:

nproc
4

This isn't fool-proof. If a core is "unavailable" (whatever that means), it won't be reported.

I believe this also reports "logical" (hyperthread) cores too, but I'm not certain.

grep -c proc /proc/cpuinfo

This will count logical cores.

That usually means num_cores * 2 - because each hyperthread-enabled core counts twice.

grep -c processor /proc/cpuinfo

This counts the occurances of the word 'processor' in the text of /proc/cpuinfo, which looks like this:

cat /proc/cpuinfo
processor : 0
model name  : ARMv7 Processor rev 5 (v7l)
BogoMIPS  : 51.20
Features  : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part  : 0xc07
CPU revision  : 5

...

Hardware  : BCM2709
Revision  : a01041
Serial    : 00000000e3a06ac9

cat /proc/cpuinfo | grep cores

This doesn't work on Raspberry Pi, but it will on most HyperThread-enabled systems.

cat /proc/cpuinfo | grep 'cpu cores' | cut -d ':' -f2 | cut -d' ' -f2

lscpu: linux

I don't have a multi-core machine to test this on, but this should work in most cases:

NUM=$(lscpu --parse=core | grep -v '^#' | sort -nr | head -n 1)
NUM=$(($NUM + 1))

If you had a really weird setup - say a 2 socket machine where 1 cpu had 2 cores that don't support hyper-threading and the other had 3 cores that do support it and you needed an accurate count... you could parse this output and get accurate results.

lscpu --parse=cpu,core,socket | grep -v '^#'

Note: lscpu uses the term cpu to mean thread (on a cpu core). It uses socket to mean a physical cpu die and core to mean a cpu core.

Others

There are approximately 1 trillion brazillion million billion eleventy six other ways to do this, but they pretty much all involve somehow parsing either /proc/cpuinfo or lscpu.

By AJ ONeal

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