sysv_signal(3)

✨ sysv_signal(3) ✨

okay bestie, so this one lives in the Library Functions Manual and it's giving "vintage but make it cursed" 💅 it's a libc function, we're in section 3, let's GO 🦋

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🌸 NAME 🌸

sysv_signal — signal handling with System V semantics

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🎀 LIBRARY 🎀

Standard C library (libc, -lc)

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✨ SYNOPSIS ✨

#define _GNU_SOURCE         /* See feature_test_macros(7) */
#include <signal.h>

typedef typeof(void (int))  *sighandler_t;

sighandler_t sysv_signal(int signum, sighandler_t handler);

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💖 DESCRIPTION 💖

So sysv_signal() takes the exact same arguments and does the exact same job as signal(2). Same energy, same vibe, same task. 🫶

BUT. And it's a big but. sysv_signal() serves you the System V unreliable signal semantics — lowercase unreliable, that's literally the name, not me being shady. Here's what that actually means:

• a) the disposition of the signal gets reset to the default when the handler is invoked 😭
• b) delivery of further instances of the signal is not blocked while the signal handler is executing 🙈
• c) and if the handler interrupts (certain) blocking system calls, then the system call is not automatically restarted 💀

like... that's the whole thing. that's the function. iconic in a historical-artifact way ⭐

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🔥 RETURN VALUE 🔥

sysv_signal() hands you back the previous value of the signal handler — or SIG_ERR if something went wrong 👍

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🍓 ERRORS 🍓

As for signal(2). (yes queen, go read that one, it's got the receipts 📜)

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👑 ATTRIBUTES 👑

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

• Interface: sysv_signal()
• Attribute: Thread safety
• Value: MT-Safe

so like, thread-safe bestie, we love that for her 💜 (the table said it, I'm just relaying it, no cap)

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🌈 VERSIONS 🌈

• Use of sysv_signal() should be avoided; use sigaction(2) instead. yes fr fr, this is the actual advice, straight from the source, no editorializing from me 🙏
• On older Linux systems, sysv_signal() and signal(2) were equivalent. But on newer systems, signal(2) provides reliable signal semantics; see signal(2) for details. glow-up arc ✨
• The use of sighandler_t is a GNU extension; this type is defined only if the _GNU_SOURCE feature test macro is defined. so if you forgot your #define _GNU_SOURCE, that type just... isn't there. vibe check failed 💅

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🧚 STANDARDS 🧚

None.

(that's it. that's the whole standard. it's giving unstandardized and proud 🎀)

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💫 SEE ALSO 💫

• sigaction(2)
• signal(2)
• bsd_signal(3)
• signal(7)

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⚠️ real talk for one sec: the doc literally says to avoid sysv_signal() and go to sigaction(2) instead. this isn't me being dramatic, it's in VERSIONS. protect your signal handling bestie 🫶

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and that's the whole page!! 🌸 this lil slice of the Linux man-pages 6.20, dated 2026-02-08, is done and dusted. go forth and sigaction(2) instead, mwah 💖🦋✨