How to obtain the number of CPUs/cores in Linux from the command line?

Question

I have this script, but I do not know how to get the last element in the printout:

cat /proc/cpuinfo | awk '/^processor/{print $3}'

The last element should be the number of CPUs, minus 1.

Answer 1

grep -c ^processor /proc/cpuinfo

will count the number of lines starting with "processor" in /proc/cpuinfo

For systems with hyper-threading, you can use

grep ^cpu\\scores /proc/cpuinfo | uniq |  awk '{print $4}'

which should return (for example) 8 (whereas the command above would return 16)

Answer 2

Processing the contents of /proc/cpuinfo is needlessly baroque. Use nproc which is part of coreutils, so it should be available on most Linux installs.

Command nproc prints the number of processing units available to the current process, which may be less than the number of online processors.

To find the number of all installed cores/processors use nproc --all

On my 8-core machine:

$ nproc --all
8

Answer 3

The most portable solution I have found is the getconf command:

getconf _NPROCESSORS_ONLN

This works on both Linux and Mac OS X. Another benefit of this over some of the other approaches is that getconf has been around for a long time. Some of the older Linux machines I have to do development on don't have the nproc or lscpu commands available, but they have getconf.

^{Editor's note: While the getconf utility is POSIX-mandated, the specific _NPROCESSORS_ONLN and _NPROCESSORS_CONF values are not. That said, as stated, they work on Linux platforms as well as on macOS; on FreeBSD/PC-BSD, you must omit the leading _.}