PR_CAPBSET_READ(2const)

✨ PR_CAPBSET_READ(2const) ✨

okay bestie, pull up a chair (or like, a terminal tab) because we're talking about PR_CAPBSET_READ, a <pink>prctl(2)</pink> operation that lives in the <hotpink>2const</hotpink> pages (that (2const) is just the man-pages way of saying "this is one of the prctl constants, it's not its own syscall, don't come for me"). It's giving very niche, very powerful, very 💅 "I know what a capability bounding set is" energy. Let's go. 🦋

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🌸 NAME 🌸

PR_CAPBSET_READ — read the calling thread's capability bounding set. like, literally just peek at it. no touching. reading only. 👑

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📚 LIBRARY 📚

Standard C library (libc, -lc). the classic. the moment. nothing sketchy, nothing exotic. 🎀

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✨ SYNOPSIS ✨

#include <linux/prctl.h>  /* Definition of PR_* constants */
#include <sys/prctl.h>

int prctl(PR_CAPBSET_READ, long cap);

yes, you call prctl() — the one function, the icon — and you hand it PR_CAPBSET_READ plus a long cap and it's gonna tell you things. 🔮

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💖 DESCRIPTION 💖

so here's the tea. PR_CAPBSET_READ returns 1 if the capability you named in cap is in the calling thread's capability bounding set, or 0 if it is not. that's it. that's the whole plot. boolean moment. true or false. ate. ✅❌

the capability constants you'd pass as cap are defined in <linux/capability.h> — that's where you go to find the actual names, bestie, don't be out here guessing numbers. 📖

and now the part that actually matters, the lore: the capability bounding set dictates whether the process can receive the capability through a file's permitted capability set on a subsequent call to execve(2). so like… this set is the bouncer 🧍 and execve(2) is the party. if your capability isn't on the list, it is NOT getting in through that file's permitted capability set. no cap. 🚫🎟️

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🫶 RETURN VALUE 🫶

• On success, this call returns the boolean value described above — so 1 or 0, depending on whether cap is chillin' in the bounding set.
• On error, -1 is returned, and errno is set to indicate the error. 😭 (classic, honestly)

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💀 ERRORS 💀

• EINVAL — cap does not specify a valid capability. you passed it something fake, babe. it's not a vibe check it can pass. 🚩

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🌈 VERSIONS 🌈

there's a higher-level interface layered on top of this operation, and it's provided in the libcap(3) library in the form of cap_get_bound(3). so if you want the fancy wrapper instead of rawdogging prctl(), that's your girl. ✨

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⭐ STANDARDS ⭐

Linux. obviously. it's giving penguin. 🐧

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🎀 HISTORY 🎀

Linux 2.6.25. an elder. a legend. still serving. 👑

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👀 SEE ALSO 👀

• prctl(2)
• PR_CAPBSET_DROP(2const)
• libcap(3)
• cap_get_bound(3)

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fr fr reminder: this page is read-only behavior — the "READ" is right there in the name. if you wanna change the bounding set instead of just looking at it, go see PR_CAPBSET_DROP(2const). 💅

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okay that's the whole thing, go forth and check your bounding set, you main character. 🦋💖

this iconic little page came to you courtesy of Linux man-pages 6.20, dated 2026-02-08 — mwah, no notes. 🎀✨