getsid(2)

💖 getsid — get session ID 💖

okay bestie, so you know how every process on a Unix system is living its little life inside a session? yeah. this page is about peeking at which one. it's giving "who's your group chat admin" but for processes. no cap.

manual name: getsid(2) — that's the system calls manual, section 2, the cool one. 🫶

📚 LIBRARY

Standard C library (libc, -lc). just your normal libc, nothing exotic, we love that for her. ✨

🌸 SYNOPSIS

#include <unistd.h>

pid_t getsid(pid_t pid);

Feature Test Macro Requirements for glibc (see feature_test_macros(7))

so lowkey glibc is gatekeeping this function behind macros, and you do need to set one or it won't show up. here's the tea:

• getsid():
  • _XOPEN_SOURCE >= 500
  • || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

yeah that || is doing the heavy lifting. pick a lane, either one works. 💅

🦋 DESCRIPTION

getsid() returns the session ID of the process with process ID pid. simple as that, she's a one-job icon.

and the bestie detail: if pid is 0, then getsid() returns the session ID of the calling process. it's like asking "what's my session" instead of pointing at someone else. main character energy, honestly. 👑

⭐ RETURN VALUE

• on success: a session ID comes back, slay ✨
• on error: (pid_t) -1 is returned, and errno gets set to tell you what went wrong 😭

💀 ERRORS

here's the vibe check on what can go sideways:

• EPERM — so a process with process ID pid does exist, but it's not in the same session as the calling process, and the implementation considers that a whole error. like, blocked, respectfully. 🚫
• ESRCH — no process with process ID pid was found. it's not there. ghosted. literally nobody home. 🫥

🌈 VERSIONS

okay so on Linux specifically: Linux does not return EPERM. noted, periodt.

👑 STANDARDS

POSIX.1-2024. certified, standardized, iconic.

🧚 HISTORY

she has lore: SVr4, SUSv1, Linux 2.0, POSIX.1-2001 XSI, POSIX.1-2008. a whole ancestry, we stan a legacy queen. 💜

🎀 NOTES

if you wanna actually understand what sessions and session IDs are, go read credentials(7) — that's where the whole concept gets explained. trust, iykyk. 📖

🔥 SEE ALSO

• getpgid(2)
• setsid(2)
• credentials(7)

---

k that's the whole page bestie, you're officially a session ID expert now, no cap 💅

this was brought to you by Linux man-pages 6.20, dated 2026-02-08 — stay curious, stan your syscalls, and don't forget your feature test macros or it literally will not compile, mwah 🎀💖✨