PR_CAP_AMBIENT_IS_SET(2const)

💖 PR_CAP_AMBIENT_IS_SET(2const) 💖

okay bestie, so you found a 2const page — those are the lil' constant-flavored corner pages of the Linux man-pages project, and this one is all about peeking at your own ambient capabilities. no cap, it's a whole vibe check for privileges. 🦋

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✨ NAME ✨

PR_CAP_AMBIENT_IS_SET — read the ambient capability set of the calling thread 👑

like, of the calling thread specifically. it's giving main character energy but only for the thread that actually made the call. 💅

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📚 LIBRARY 📚

Standard C library (libc, -lc) 🌸

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🎀 SYNOPSIS 🎀

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

int prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, long cap, 0L, 0L);

so yeah, you're calling the big prctl(2) and handing it PR_CAP_AMBIENT as the operation, with PR_CAP_AMBIENT_IS_SET as the sub-operation. the 0L, 0L at the end are just vibing, they're unused here. ✨

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💜 DESCRIPTION 💜

This call returns 1 if the capability in cap is in the ambient capability set, and 0 if it is not. that's it. that's the whole thing. binary answer, no small talk. 💀

ngl this is the most lowkey useful lil' query ever — "is this specific capability in my ambient set, yes or no?" and boom, you get a boolean back. periodt. 🫶

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🍓 RETURN VALUE 🍓

On success, this call returns the boolean value described above (so like, 1 or 0, no in-between bestie). 😭

On error, -1 is returned, and errno is set to indicate the error. so always always always check your errno, i'm begging 🧚

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⚠️ ERRORS ⚠️

• EINVAL — cap does not specify a valid capability. so if you handed it a capability that doesn't exist, this is the ✨gentle✨ way it tells you to try again. 🙈

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🌈 VERSIONS 🌈

See PR_CAP_AMBIENT(2const). 🦋 (go read the parent page, it has the whole ambient-capabilities lore, iykyk)

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⭐ STANDARDS ⭐

Linux. just Linux. that's the standard. 👑

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🔥 HISTORY 🔥

Linux 4.3. it's been here since 4.3, serving bools and minding its business. 💖

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👀 SEE ALSO 👀

• prctl(2)
• PR_CAP_AMBIENT(2const)
• libcap(3)

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real talk: this call only ever reads. it does not change your ambient set — it just tells you what's in there. no cap, purely a read-only vibe check ✨

and that's the tea, bestie — Linux man-pages version 6.20, dated 2026-02-08. slay, go forth and check your ambient capabilities responsibly 💅🎀🌸