Intro To 'nproc' Command In Linux

2023-07-15 - By Robert Elder

I use the 'nproc' command to show many processors my machine has:

nproc

A Typical Use Case

On my machine, the 'nproc' command prints the value 8:

I can check the contents of '/proc/cpuinfo' to obtain my CPU's model number and compare the value of 8 against the official documentation for my processor:

cat /proc/cpuinfo | grep 'model name'

As you can see from above, my CPU is an 'i5-10300H', and the documentation shows that 8 is indeed the number of logical CPU cores that my computer has. However, the number of physical cores in my CPU is 4.

Options & Environment Variables

The value returned by the 'nproc' command can also be influenced by the following two environment variables:

OMP_NUM_THREADS=999 nproc

OMP_THREAD_LIMIT=7 nproc

It can also be influenced by 'all' flag:

OMP_THREAD_LIMIT=7 nproc --all

and the 'ignore' flag:

OMP_THREAD_LIMIT=7 nproc --all --ignore=5

Unlike many other commands, the 'nproc' command is not included in the POSIX standard. In the GNU coreutils implementation of the 'nproc' command, you can see that there are many different system calls for every different platform that the 'nproc' command can run on. Different software platforms or BIOS settings could affect the value returned by the 'nproc' command. Furthermore, concepts like hyperthreading, or power efficiency features could further complicate the process of accurately counting CPU cores.

And that's why the 'nproc' command is my favourite Linux command.

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