getusershell(3)

💖 getusershell(3) 💖

okay bestie, listen — this is getusershell / setusershell / endusershell from the Library Functions Manual, and it's literally the bouncer-at-the-club of Unix login shells. you in the libc? you're gonna wanna know who's allowed in. 🎀

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✨ NAME ✨

getusershell, setusershell, endusershell — get permitted user shells 💅

📚 LIBRARY 📚

Standard C library (libc, -lc) — the classic, no cap.

🦋 SYNOPSIS 🦋

#include <unistd.h>

char *getusershell(void);
void setusershell(void);
void endusershell(void);

🌸 Feature Test Macro Requirements for glibc 🌸

(peep feature_test_macros(7) if you need the lore, bestie)

• getusershell(), setusershell(), endusershell():
  • Since glibc 2.21:
    • _DEFAULT_SOURCE
  • In glibc 2.19 and 2.20:
    • _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
  • Up to and including glibc 2.19:
    • _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)

ngl the macro situation is giving ✨generational trauma✨ but that's just how glibc grew up.

👑 DESCRIPTION 👑

so here's the tea.

The getusershell() function returns the next line from the file /etc/shells, opening the file if necessary. that line is supposed to contain the pathname of a valid user shell — like, the receipts of who's even allowed to log in. 🫶

And here's the iconic plot twist: if /etc/shells does not exist or is unreadable, getusershell() behaves as if /bin/sh and /bin/csh were listed in the file. so it just goes "fine, these two then" and carries on, main character energy fr fr. 😭

The setusershell() function rewinds /etc/shells. ⏪ rewinding the vibe check back to the start.

The endusershell() function closes /etc/shells. 🚪 and that's the door shut, bye.

🔥 RETURN VALUE 🔥

The getusershell() function returns NULL on end-of-file. that's it, that's the whole clause. when the list runs out, it hits you with the NULL and you move on with your life. 💀

🍓 FILES 🍓

• /etc/shells

💜 ATTRIBUTES 💜

For an explanation of the terms used in this section, see attributes(7). (iykyk)

• Interface: getusershell(), setusershell(), endusershell()
  • Attribute: Thread safety
  • Value: MT-Unsafe

so uh, not thread safe, bestie. don't be sharing these across threads like they're a communal scrunchie. 🙈

⭐ STANDARDS ⭐

None. 😌 not a single one. it simply is what it is.

🌈 HISTORY 🌈

4.3BSD. old money, honestly. vintage icon behavior. 👑

💫 SEE ALSO 💫

• shells(5)

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and that's a wrap on getusershell(3)! remember: this whole page came straight from Linux man-pages 6.20, dated 2026-02-08. slay, stay safe, and keep your shells valid 💖✨🎀🦋