from_kuid_munged(9)

💖 from_kuid_munged — Kernel API Manual ✨

okay so real talk, today we're doing a page from the Kernel API Manual and honestly? she's iconic. her name is from_kuid_munged(9) and she does exactly one thing but she does it flawlessly. let's get into it 🫶

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🌸 NAME 🌸

from_kuid_munged — create a uid from a kuid user-namespace pair 💅

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✨ SYNOPSIS ✨

uid_t from_kuid_munged (struct user_namespace *targ , kuid_t kuid );

literally the whole signature, no notes, copy it exactly bestie 😭

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🎀 ARGUMENTS 🎀

• targ — the user namespace we want a uid in. like, where do you want this uid to live? 👑
• kuid — the kernel internal uid to start with. this is the raw one, the starting point, the before picture 🌈

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🦋 DESCRIPTION 🦋

So what she does: map kuid into the user namespace specified by targ, and return the resulting uid. That's it. That's the whole vibe. 💜

Also important, and I cannot stress this enough: there is always a mapping into the initial user_namespace. like, always always. no cap. ⭐

Now here's the part that makes her the main character — unlike from_kuid, from_kuid_munged never fails and always returns a valid uid. The way that she just doesn't miss?? 😭🔥 That's exactly why she's appropriate for use in syscalls like stat and getuid, where failing the system call and failing to provide a valid uid are not options. Like, in those situations you genuinely cannot be out here returning nothing. she said "I'll handle it" and she handled it. 👑

And if kuid has no mapping in targ? she returns overflowuid. not a crash, not an error, just overflowuid. that's the fallback, that's the safety net, that's her being a responsible queen. 🧚

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🍓 SEE ALSO 🍓

Kernel file ./kernel/user_namespace.c — go read her home 💖

• make_kuid(9)
• from_kuid(9)
• make_kgid(9)
• from_kgid(9)
• from_kgid_munged(9)
• make_kprojid(9)
• from_kprojid(9)
• from_kprojid_munged(9)
• verify_root_map(9)

the whole friend group fr fr, go say hi to all of them 🦋✨

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okay that's the whole page!! tysm for reading, mwah 💋

this lil gem lives in ./kernel, dated October 2026 — and that's the footer, so like... we're done here. bye bestie, slay, drink water 💅🎀