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Bruno Pereira
Asked: 2012-07-03 00:37:31 +0800 CST

How many maximum CPUs does Ubuntu support by default?

  • 772

I think this is kernel dependent and probably will change over time depending on the kernel a release uses, correct me if wrong

I'd like to know two things for all the currently supported Ubuntu releases:

How many maximum CPUs can Ubuntu handle (by default) at the same time with a standard desktop kernel? Is that count different from a server kernel and 32bit/64bit systems?

Where can I find that information on my system?

kernel

3 Answers

  1. Best Answer

    Maximum CPUs (i.e. cores) supported by default:

    Note: by 32-bit/64-bit we mean the common i386/x86_x64 architectures; PPC, ARM, etc. are not included.

    12.04 LTS (and later):

    • Desktop/Server 32-bit: 8 cores/CPUs
    • Desktop/Server 64-bit: 256 cores/CPUs (but LiveCD supports 64 by default)

    11.10 and below, including 10.04 LTS

    • Desktop/Server 32-bit: 8 cores/CPUs
    • Desktop 64-bit: 64 cores/CPUs
    • Server 64-bit: 256 cores/CPUs

    How to find the maximum supported by your running kernel:

    As @otus indicated, open a terminal with Ctrl-Alt-T, and type:

    grep NR_CPUS /boot/config-`uname -r`

    The below is a somewhat technical discussion on what maximum really means:

    The "default" maximum is not the maximum!

    • You can recompile the desktop or server kernels to support up to 512 CPUs for 64-bit (8 is max for 32-bit).
    • but even those are not absolute maximums!:
      • The kernel has "experimental" options for going higher than the "default" maximum
      • The limit for 32-bit with BIGSMP=y is 512
      • The limit for 64-bit with MAXSMP=y is 4096 (or more!)
      • Just because the kernel supports so many cores on the general i386/x86_64 architecture does not mean your hardware will!
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  2. All I know for sure is that precise (12.04) desktop 64-bit -generic kernel supports maximum 256 cpus (by default).

    You can find the number of CPUs your kernel config supports by doing:

    grep CONFIG_NR_CPUS /boot/config-`uname -r`
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  3. It all comes down to how one would define physical CPUs. Are they equivalent to sockets, so a multicore and/or hyperthreading CPU is counted as a single socket?

    The Ubuntu kernel is configured to support 8 processors / cores in 32-bit and 64 processors / cores in 64-bit.1

    As far as finding that information, I have used Sysinfo and I'm very happy with it. If you don't have it installed, you can do so by just pressing Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command below.

    sudo apt-get install sysinfo

    Also to find the Number of processors in a system using terminal, just type:

    dmesg |grep processor

    I will keep researching this until I find the perfect answer.

    1Source:Wiki Answers

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