CURLOPT_TCP_KEEPALIVE(3)

💖 CURLOPT_TCP_KEEPALIVE — TCP keep-alive probing 💖

okay bestie, this is a page from the libcurl manual, specifically CURLOPT_TCP_KEEPALIVE(3). yes, the all-caps name is a lot, but she's iconic, we move.

---

✨ NAME ✨

CURLOPT_TCP_KEEPALIVE — literally just TCP keep-alive probing. that's it. that's the whole vibe 🫶

🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TCP_KEEPALIVE, long probe);

💅 DESCRIPTION 💅

so you pass a long. that's the move. 🎀

• if you set it to 1, TCP keepalive probes are used. like, your connection is out there poking the other side going "hey bestie, u still there?? 👀"
• the delay and frequency of those probes can be controlled by the CURLOPT_TCP_KEEPIDLE(3), CURLOPT_TCP_KEEPINTVL(3), and CURLOPT_TCP_KEEPCNT(3) options — provided the operating system supports them. that caveat is doing heavy lifting ngl, some OSes just don't wanna 💀
• set it to 0 (this is the default behavior) to disable keepalive probes. dead it. no probes. ✨

🦋 DEFAULT 🦋

0

like, off. no cap. she's chill by default.

🌈 PROTOCOLS 🌈

This functionality affects tcp only. just tcp. nobody else invited to this party 🙈

⭐ EXAMPLE ⭐

this is the whole thing, verbatim, no edits, she's beautiful:

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

    /* enable TCP keep-alive for this transfer */
    curl_easy_setopt(curl, CURLOPT_TCP_KEEPALIVE, 1L);

    /* keep-alive idle time to 120 seconds */
    curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 120L);

    /* interval time between keep-alive probes: 60 seconds */
    curl_easy_setopt(curl, CURLOPT_TCP_KEEPINTVL, 60L);

    /* maximum number of keep-alive probes: 3 */
    curl_easy_setopt(curl, CURLOPT_TCP_KEEPCNT, 3L);

    curl_easy_perform(curl);
  }
}

look at her go. 1L turns it on, 120L idle seconds, 60L between probes, 3L max probes. ate. 🔥

🎀 AVAILABILITY 🎀

Added in curl 7.25.0. vintage-ish. still slays.

💜 RETURN VALUE 💜

curl_easy_setopt(3) returns a CURLcode indicating success or error. that's the messenger, she tells you how it went.

• CURLE_OK (0) means everything was OK. we love a zero. 🫶
• non-zero means an error occurred — see libcurl-errors(3) for the full breakdown of what went wrong.

lowkey important: don't ignore a non-zero return, bestie, that's your program telling you something's up 😭

🧚 SEE ALSO 🧚

• CURLOPT_LOW_SPEED_LIMIT(3)
• CURLOPT_MAX_RECV_SPEED_LARGE(3)
• CURLOPT_TCP_KEEPCNT(3)
• CURLOPT_TCP_KEEPIDLE(3)
• CURLOPT_TCP_KEEPINTVL(3)

go read those too, they're the friend group, they come as a set 💖

---

and that's the page!! brought to you by libcurl, dated 2026-10-12, and originally filed under CURLOPT_TCP_KEEPALIVE(3). mwah 💋 go keep those TCP connections alive, queen 👑✨