SSL_CTX_FLUSH_SESSIONS(3)

💅 SSL_CTX_FLUSH_SESSIONS(3) 💅

okay so this is a page from the Library Functions Manual (the libssl / libcrypto girlies, you know the ones) and it's literally about cleaning out expired sessions. it's giving spring cleaning but for your TLS cache. 🧹✨

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🌸 NAME 🌸

SSL_CTX_flush_sessions — remove expired sessions, bestie. that's it, that's the whole vibe. 🗑️

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✨ SYNOPSIS ✨

kay so first you gotta pull in the header, the library is libssl libcrypto and the include is this:

#include <openssl/ssl.h>

and then the function itself, no cap:

void
SSL_CTX_flush_sessions(SSL_CTX *ctx, long tm);

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🦋 DESCRIPTION 🦋

so SSL_CTX_flush_sessions() does a whole little walk-through of the session cache of ctx and removes every session that's expired at time tm. like a bouncer checking IDs but for expirations. 👑✨

if it's enabled, the internal session cache will collect all the sessions established up to the specified maximum number (peep SSL_CTX_sess_set_cache_size(3) for that one). and here's the thing — once sessions are expired they are not getting reused, so lowkey they should just be removed from the cache to save resources. iconic resource management. 💖

and you've got two ways to do it:

• automatically, whenever 255 new sessions were established (see SSL_CTX_set_session_cache_mode(3))
• or manually, by calling SSL_CTX_flush_sessions() yourself

the parameter tm specifies the time that should be used for the expiration test — and in most cases the actual time given by time(0) will be used. fr fr, that's the usual move. ⏰

heads up: SSL_CTX_flush_sessions() will only check sessions stored in the internal cache. when a session is found and removed, though, the remove_session_cb does get called to synchronize with the external cache (see SSL_CTX_sess_set_get_cb(3)). so the external cache still gets its little notification, periodt. 🫶

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🌈 SEE ALSO 🌈

go read these next, iykwim:

• ssl(3)
• SSL_CTX_sess_set_get_cb(3)
• SSL_CTX_set_session_cache_mode(3)
• SSL_CTX_set_timeout(3)

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🎀 HISTORY 🎀

SSL_CTX_flush_sessions() first appeared in SSLeay 0.8.0 and has been available since OpenBSD 2.4. she's been around a minute, and honestly? she ate. 💅⭐

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and that's the whole page bestie 🫶 this drop was brought to you by Debian, dated June 8, 2025, filed under SSL_CTX_FLUSH_SESSIONS(3) — go flush those sessions, mwah 💖🧚✨