PR_CAP_AMBIENT_LOWER(2const)

💅 PR_CAP_AMBIENT_LOWER — lower the ambient capability set of the calling thread 💅

okay bestie, welcome to PR_CAP_AMBIENT_LOWER — a prctl(2) sub-operation, i.e. one of those 2const manual page girlies (yes, that's the manual section name, we're in the (2const) section, slay). This one is all about taking a capability OUT of your thread's ambient set. Let's get into it 🎀

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✨ LIBRARY ✨

Standard C library — libc, -lc. The classic. Nothing fancy, she's just vibing in libc 🦋

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📜 SYNOPSIS 📜

okay so here's the whole shape of it, literally:

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

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

notice how the third arg is where cap goes and the last two are 0L, 0L — yes, you HAVE to pass those zeroes, they're not optional-optional, they're just chillin' there being 0L 😌

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🌸 DESCRIPTION 🌸

So the entire plot: the capability you name in cap gets removed from the ambient capability set. That's it. That's the whole job. You point at a capability, and it's gone from ambient. Periodt 💅

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🔥 RETURN VALUE 🔥

• On success — you get 0 back. Iconic. Main character energy ✨
• On error — you get -1, and errno is set to tell you what went wrong. Rude but informative 😭

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💀 ERRORS 💀

• EINVAL — cap does not specify a valid capability. Like girl, that's not a real capability, try again 🙈

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🧚 VERSIONS 🧚

lowkey this section is just a redirect — see PR_CAP_AMBIENT(2const). All the version lore lives over there 🫶

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👑 STANDARDS 👑

Linux. That's it, that's the standard. Linux only, no cap 🐧

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⭐ HISTORY ⭐

Arrived in Linux 4.3. A lil vintage, a lil retro, still serving 🎀

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🌈 SEE ALSO 🌈

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

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okay that's the whole page, you ate that 🍓 remember: cap in, capability out of the ambient set, check errno if you get -1, and don't forget those two 0Ls or the kernel will simply not hear you 💜

this page is from Linux man-pages 6.20, dated 2026-02-08, and it's the PR_CAP_AMBIENT_LOWER(2const) one — mwah, bye bestie 💖✨