{
    "mode": "man",
    "parameter": "CPUID",
    "section": "4",
    "url": "https://www.chedong.com/phpMan.php/man/CPUID/4/json",
    "generated": "2026-06-12T06:24:19Z",
    "sections": {
        "NAME": {
            "content": "cpuid - x86 CPUID access device\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "CPUID provides an interface for querying information about the x86 CPU.\n\nThis device is accessed by lseek(2) or pread(2) to the appropriate CPUID level and reading in\nchunks of 16 bytes.  A larger read size means multiple reads of consecutive levels.\n\nThe lower 32 bits of the file position is used as the incoming %eax, and the upper 32 bits of\nthe file position as the incoming %ecx, the latter is intended for \"counting\" eax levels like\neax=4.\n\nThis driver uses /dev/cpu/CPUNUM/cpuid, where CPUNUM is the minor number, and on an  SMP  box\nwill direct the access to CPU CPUNUM as listed in /proc/cpuinfo.\n\nThis  file is protected so that it can be read only by the user root, or members of the group\nroot.\n",
            "subsections": []
        },
        "NOTES": {
            "content": "The CPUID instruction can be directly executed by a program using inline assembler.   However\nthis device allows convenient access to all CPUs without changing process affinity.\n\nMost  of  the  information  in  cpuid  is  reported  by  the  kernel in cooked form either in\n/proc/cpuinfo or through subdirectories  in  /sys/devices/system/cpu.   Direct  CPUID  access\nthrough this device should only be used in exceptional cases.\n\nThe  cpuid driver is not auto-loaded.  On modular kernels you might need to use the following\ncommand to load it explicitly before use:\n\n$ modprobe cpuid\n\nThere is no support for CPUID functions that require additional input registers.\n\nVery old x86 CPUs don't support CPUID.\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "cpuid(1)\n\nIntel Corporation, Intel 64 and IA-32 Architectures Software Developer's  Manual  Volume  2A:\nInstruction Set Reference, A-M, 3-180 CPUID reference.\n\nIntel Corporation, Intel Processor Identification and the CPUID Instruction, Application note\n485.\n",
            "subsections": []
        },
        "COLOPHON": {
            "content": "This page is part of release 5.10 of the Linux  man-pages  project.   A  description  of  the\nproject,  information about reporting bugs, and the latest version of this page, can be found\nat https://www.kernel.org/doc/man-pages/.\n\n\n\nLinux                                        2019-08-02                                     CPUID(4)",
            "subsections": []
        }
    },
    "summary": "cpuid - x86 CPUID access device",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "cpuid",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/cpuid/1/json"
        }
    ]
}