KEYCTL_JOIN_SESSION_KEYRING(2const)

💖 KEYCTL_JOIN_SESSION_KEYRING 💖

okay bestie, so you know how a process has a session keyring it's subscribed to? This is the keyctl(2) operation that swaps it out for a whole new one. Glow-up time for your keyring. 👑

It's a KEYCTL_* constant from the Linux kernel's key management syscall family — the page lives in section 2const, so if you were looking for the manual name, it's keyctl_join_session_keyring(2const). ✨

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📚 LIBRARY

Standard C library (libc, -lc). Yep, the basic one, no extras needed. 💅

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✨ SYNOPSIS ✨

#include <linux/keyctl.h>  /* Definition of KEY* constants */
#include <sys/syscall.h>   /* Definition of SYS_* constants */
#include <unistd.h>

long syscall(SYS_keyctl, KEYCTL_JOIN_SESSION_KEYRING,
             char *_Nullable desc);

note that desc is _Nullable, so handing over a NULL is a whole valid vibe here, not a mistake. 🫶

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🌸 DESCRIPTION 🌸

So the whole point: replace the session keyring this process subscribes to with a new session keyring. That's it. That's the gig. New keyring, who dis. 💖

Now here's where it branches, and this part is important, so pay attention bestie:

• If desc is NULL, an anonymous keyring with the description "_ses" gets created, and the process is subscribed to that keyring as its session keyring, displacing whatever session keyring it had before. Say bye to the old one. 👋
• Otherwise, desc is treated as the description (aka the name) of a keyring, and then the behavior goes like this:
  • If a keyring with a matching description exists, the process will attempt to subscribe to that keyring as its session keyring if possible; if that is not possible, an error is returned. And heads up — in order to subscribe to that keyring, the caller must have search permission on the keyring. No permission, no entry, periodt. 🔒
  • If a keyring with a matching description does not exist, then a brand new keyring with the specified description is created, and the process is subscribed to that keyring as its session keyring. Manifesting a keyring into existence, iconic behavior honestly. 🌈

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🎀 RETURN VALUE 🎀

• On success, you get the ID of the joined session keyring. Treasure it. 👑
• On error, -1 is returned, and errno is set to indicate the error. Classic. 💀

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🦋 VERSIONS 🦋

There's a cute lil wrapper for this over in the libkeyutils library: keyctl_join_session_keyring(3). Use it if you don't wanna rawdog the syscall. 🙈

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⭐ STANDARDS ⭐

Linux. Just Linux. That's the whole standard. 💜

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🌸 HISTORY 🌸

Linux 2.6.10 — this has been around since way back, it's a certified elder. 👑

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💅 SEE ALSO 💅

• keyctl(2)
• keyctl_join_session_keyring(3)

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okay that's the whole thing, you're so welcome, go forth and subscribe to keyrings responsibly 🫶

this was brought to you by Linux man-pages 6.20, dated 2026-02-0, mwah 💋