{
    "mode": "man",
    "parameter": "cpuid",
    "section": "4",
    "url": "https://www.chedong.com/phpMan.php/man/cpuid/4/json",
    "generated": "2026-10-08T23:49:04Z",
    "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\nEarly  i486  CPUs  do  not  support the CPUID instruction; opening this device for those CPUs\nfails with EIO.\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\nLinux man-pages 6.7                          2024-01-05                                     cpuid(4)",
            "subsections": []
        }
    },
    "summary": "cpuid - x86 CPUID access device",
    "flags": [],
    "examples": [],
    "see_also": []
}