Physical cores in linux

How do I find physical cores in Linux?

You can use one of the following command to find the number of physical CPU cores including all cores on Linux:

1. lscpu command.
2. cat /proc/cpuinfo.
3. top or htop command.
4. nproc command.
5. hwinfo command.
6. dmidecode -t processor command.
7. getconf _NPROCESSORS_ONLN command.

How do I know which processors are physical cores?

Press the Ctrl + Shift + Esc keys simultaneously to open the Task Manager. Go to the Performance tab and select CPU from the left column. You’ll see the number of physical cores and logical processors on the bottom-right side.

How do I know if my cores are Hyperthreaded?

The best way to do it is just to benchmark it. Write any trivial program that uses 2 threads. Then bind the threads to two cores. If the performance drops significantly between a pair of cores versus another pair, then you know those two cores are on the same physical core.

Does free memory exist on Linux?

In LINUX, there exists a command line utility for this and that is free command which displays the total amount of free space available along with the amount of memory used and swap memory in the system, and also the buffers used by the kernel. This is pretty much what free command does for you.

How to check the number of CPU cores in Linux?

You can use one of the following command to find the number of physical CPU cores including all cores on Linux: lscpu command. cat /proc/cpuinfo. top or htop command. nproc command. hwinfo command.

core id show the identifier of the current core, out to a total of cpu cores. You can use this information to correlate which virtual processor goes into a single core.

How many threads are there in Linux system?

Total threads: 16 ( CPU core [8] * Thread per core [2]) The lscpu command gathers CPU architecture information from sysfs, /proc/cpuinfo and other sources. To view use the cat command and more command as follows:

What’s the difference between core ID and physical ID?

physical id shows the identifier of the processor. Unless you have a multiprocessor setup (having two separate, physical processor in a machine), it will always be 0. siblings show the number of processor attached to the same physical processor. core id show the identifier of the current core, out to a total of cpu cores.

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How to know number of cores of a system in Linux?

I wanted to find out how many cores my system has, so I searched the same question in Google. I got some commands such as the lscpu command. When I tried this command, it gave me the following result:

$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 4 On-line CPU(s) list: 0-3 Thread(s) per core: 1 Core(s) per socket: 4 Socket(s): 1 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 23 Stepping: 10 CPU MHz: 1998.000 BogoMIPS: 5302.48 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 2048K NUMA node0 CPU(s): 0-3 

Which of those indicates cores of a Linux system?

Is there any other command to tell the number of cores, or am I assuming it is completely wrong?

Your image of text isn’t very helpful. It can’t be copied into an editor, and it doesn’t index very well, meaning that other users with the same problem are less likely to find the answer here. Please edit your post to incorporate the relevant text directly (preferably using copy+paste to avoid transcription errors).

@สมหวังแนวหน้า kind of a nitpick, but the the grep arg should be processor , not precessor , correct? . Thanks for the help!

12 Answers 12

To get a complete picture you need to look at the number of threads per core, cores per socket and sockets. If you multiply these numbers you will get the number of CPUs on your system.

CPUs = Threads per core X cores per socket X sockets

CPUs are what you see when you run htop (these do not equate to physical CPUs).

Here is an example from a desktop machine:

$ lscpu | grep -E '^Thread|^Core|^Socket|^CPU\(' CPU(s): 8 Thread(s) per core: 2 Core(s) per socket: 4 Socket(s): 1 

$ lscpu | grep -E '^Thread|^Core|^Socket|^CPU\(' CPU(s): 32 Thread(s) per core: 2 Core(s) per socket: 8 Socket(s): 2 

The output of nproc corresponds to the CPU count from lscpu . For the desktop machine above this should match the 8 CPU(s) reported by lscpu :

The output of /proc/cpuinfo should match this information, for example on the desktop system above we can see there are 8 processors (CPUs) and 4 cores (core id 0-3):

$ grep -E 'processor|core id' /proc/cpuinfo processor : 0 core id : 0 processor : 1 core id : 0 processor : 2 core id : 1 processor : 3 core id : 1 processor : 4 core id : 2 processor : 5 core id : 2 processor : 6 core id : 3 processor : 7 core id : 3 

The cpu cores reported by /proc/cpuinfo corresponds to the Core(s) per socket reported by lscpu . For the desktop machine above this should match the 4 Core(s) per socket reported by lscpu:

$ grep -m 1 'cpu cores' /proc/cpuinfo cpu cores : 4 

To specifically answer your question you tell how many cores you have by multiplying the number of cores you have per socket by the number of sockets you have.

Cores = Cores per socket X Sockets

For the example systems above the desktop has 4 cores:

$ echo "Cores = $(( $(lscpu | awk '/^Socket\(s\)/< print $2 >') * $(lscpu | awk '/^Core\(s\) per socket/< print $4 >') ))" Cores = 4 

$ echo "Cores = $(( $(lscpu | awk '/^Socket\(s\)/< print $2 >') * $(lscpu | awk '/^Core\(s\) per socket/< print $4 >') ))" Cores = 16 

Another useful utility is dmidecode which outputs per socket information. In the case of the server system listed above we expect to see 8 cores per socket and 16 threads per socket:

$ sudo dmidecode -t 4 | grep -E 'Socket Designation|Count' Socket Designation: CPU1 Core Count: 8 Thread Count: 16 Socket Designation: CPU2 Core Count: 8 Thread Count: 16 

The lscpu command has a number of useful options that you may like to check out, for example:

$ lscpu --all --extended $ lscpu --all --parse=CPU,SOCKET,CORE | grep -v '^#' 

See man lscpu for details.

• You need to be aware of sockets, cores and threads
• You need to be careful of the term CPU as it means different things in different contexts

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4 Ways to Find CPU Cores on Linux

The ability to find CPU cores on Linux could be helpful in not just finding out the processing power of your system, but adding compatible hardware too. We’re here to show you not just one but four different ways of figuring out the CPU cores on your Linux OS system.

The number of cores in consumer CPUs has been increasing rapidly in the past few years, with some reaching upwards of 16 cores. Having more cores is an upside but sometimes, having too many can be detrimental to our performance depending on the tasks we are trying to run.

Most consumers don’t need CPUs that have more than eight cores. The increase in core count also brought a decrease in single-core performance. And considering most consumer programs don’t use that many cores but rely solely on single-core performance—it is often better to go with a lower core count CPU that has a higher clock count.

4 Ways to Find CPU Cores on Linux

Whether you’re looking to optimize your code, see if you can run that new AAA game, or just want to know how many cores your CPU has, here are four simple ways to check how many cores your CPU has.

Using the lscpu command

If we run the lscpu command, we are bombarded with all kinds of information regarding our CPU. We can see our architecture, model name, cache, and, most importantly, our core count.

We can make this a bit cleaner by running the egrep command alongside lscpu to get just our core count, as shown in the example below.

Using the egrep command here, we input our search term, and we add the backslashes for the brackets. Otherwise, the command won’t know if we want to include those characters in the search.

The number we are given here is the number of our logical cores, not our physical cores. In our case, we have a six-core CPU with hyperthreading. This means we have six physical and six logical cores, or you could even call them imaginary cores.

This means that one core in this CPU can act like two cores, thus multiplying the overall core count.

Reading information from the /proc/cpuinfo file

Inside the /proc directory, we have a bunch of valuable files containing information about the currently running processes and details of other systems.

The /proc directory is a virtual filesystem, sometimes referred to as a process information pseudo-file system. It is created upon system boot, destroyed on shutdown, and regarded as a control and information center for the kernel.

Using the cat command, we can read information about our CPU from the cpuinfo file.

After doing that, we will be greeted with a bunch of information, similar to what lscpu gives us but much more. We can clean this up by using the grep command again.

$ cat /proc/cpuinfo | grep -m 1 'cpu cores'

Again using the egrep command, we just input our search term and add the -m flag and the input 1 for that flag. This means we simply want to see the first result presented to us. We do this because there are multiple results for this search term, although they all contain the same value, ‘6’.

As we can see here, unlike in the previous example, we are only shown the number of our physical cores.

Using the nproc command

This one is by far the easiest. If we look at the manual page for the nproc command, we can see that its primary function is to show the number of available cores.

And if we run nproc .

Again, we will be shown the number of physical and logical cores.

Using htop/top

Lastly, we can check how many cores we have by running a simple CLI utility like htop or top . This way, not only do we get to see how many cores we have, but we are also able to see their utilization in real-time.

We could see four different ways to look up the number of CPU cores on a system. Along with how to combine that with the use of the grep/egrep commands. These processes can save us time from searching for our preferred result manually and simply having it presented to us.

All of these commands have pros and cons. Some show us the total number of logical cores, while others only show us the number of our physical cores. And, of course, htop showing us the individual utilization of every core.

If you’re looking to upgrade your current CPU, we would recommend going for a CPU that has anywhere between four and eight cores if your primary goal is coding, gaming, and possibly some light production work.

Generally speaking, you don’t need more than that unless you are doing some heavy rendering/testing, and even then, it’s much better to get a higher-end GPU that will do those tasks much faster.

If this guide helped you, please share it.

Husain is a staff writer at Distroid and has been writing on all things Linux and cybersecurity for over 10 years. He previously worked as a technical writer for wikiHow. In his past time, he loves taking tech apart and see what makes them tick, without necessarily putting it all back together. LinkedIn

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