OPENSSL_FORK_PREPARE(3SSL)

💖 OPENSSL_FORK_PREPARE 💖

okay bestie, gather round, because today we're talking about the OpenSSL fork handlers — that's OPENSSL_fork_prepare, OPENSSL_fork_parent, and OPENSSL_fork_child, all chillin' in the 3SSL manual. this one's giving "niche but important", and honestly? we love her for it. 🫶

---

✨ SYNOPSIS ✨

#include <openssl/crypto.h>

so here's the tea, and it's a lil bittersweet: these functions have been deprecated since OpenSSL 3.0, and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value. (go peek at openssl_user_macros(7) for the deets, iykyk.)

void OPENSSL_fork_prepare(void);
void OPENSSL_fork_parent(void);
void OPENSSL_fork_child(void);

---

🌸 DESCRIPTION 🌸

okay so first things first: these methods are currently unused, and because of that, there are no replacement methods required or planned. no glow-up planned. no successor. she's just vibing in legacy town. 💀

here's why they exist though, because context is everything: OpenSSL has state that should be reset when a process forks. for example, the entropy pool used to generate random numbers (and therefore encryption keys) should not be shared across multiple programs. like, absolutely not, that's a whole mess. so OPENSSL_fork_prepare(), OPENSSL_fork_parent(), and OPENSSL_fork_child() are the trio that resets this internal state. 💅

now, the vibe check per platform:

• platforms without fork(2) will probably not need to use these functions at all.
• platforms with fork(2) but without pthread_atfork(3) will probably need to call them manually, as described in the following paragraph.
• platforms such as Linux that have both functions will normally not need to call these functions, because the OpenSSL library will do so automatically. main character energy, honestly. ✨

OPENSSL_init_crypto(3) will register these functions with the appropriate handler, when the OPENSSL_INIT_ATFORK flag is used. for other applications, these functions can be called directly. they should be used according to the calling sequence described by the pthread_atfork(3) documentation, which is summarized here:

• OPENSSL_fork_prepare() should be called before a fork() is done.
• after the fork() returns, the parent process should call OPENSSL_fork_parent().
• and the child process should call OPENSSL_fork_child().

periodt. that's the whole choreography. 🎀

---

🦋 RETURN VALUES 🦋

OPENSSL_fork_prepare(), OPENSSL_fork_parent() and OPENSSL_fork_child() do not return values. they're void, they're mysterious, they simply are. 💜

---

🌈 SEE ALSO 🌈

• OPENSSL_init_crypto(3)

---

⭐ HISTORY ⭐

these functions were added in OpenSSL 1.1.1. so yeah, they've been around a minute.

---

👑 COPYRIGHT 👑

Copyright 2017-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

---

and that's the whole page, bestie, no cap. mwah 💋 this was OpenSSL 4.0.3, dated 2026-09-29 — slay, drink your water, and maybe reset your entropy pool after forking. 🧚🌸