msr(4)

💅 msr(4) — the x86 CPU MSR access device, bestie

okay so this is a Kernel Interfaces Manual page, and it's about a lil special device file that lets you peek at and poke at your CPU's most private lil registers. it's giving hardware whisperer energy 🧚

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✨ NAME ✨

msr — the x86 CPU MSR access device 🦋

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🌸 DESCRIPTION 🌸

so like, /dev/cpu/CPUNUM/msr is this file that gives you an interface to read and write the model-specific registers (MSRs) of an x86 CPU. very demure, very mindful, very powerful. 💖

CPUNUM is literally just the number of the CPU you wanna access, exactly how it's listed up in /proc/cpuinfo. no cap. 👑

the way you actually do the register access is: you open the file, then seek to the MSR number as the offset in the file, and then you read or write in chunks of 8 bytes. that's the whole vibe. ✨

ngl, an I/O transfer of more than 8 bytes means multiple reads or writes of the same register. so like, don't be surprised, it's just doing it again. 🙈

this file is protected, bestie. it can be read and written only by the user root, or by members of the group root. so if you're not in the club, you're not getting in. 💅

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🎀 NOTES 🎀

important!! the msr driver is not auto-loaded. it does not just show up on its own, it's not that kind of icon. 😭

on modular kernels, you might need to run the following command to load it explicitly before you use it:

$ modprobe msr

do that first, then you're slaying. 🫶

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👑 SEE ALSO 👑

• Intel Corporation Intel 64 and IA-32 Architectures Software Developer's Manual Volume 3B Appendix B, for an overview of the Intel CPU MSRs. 📚

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okay that's the whole page, periodt. 💜 this was Linux man-pages 6.20, dated 2026-02-08, and that's the sign-off, mwah. 🎀✨