IP_MTU(2const)

💖 IP_MTU — path maximum transmission unit size 💖

okay bestie, this one's a <cyan>2const</cyan> page (it lives in the Linux man-pages 6.20 set, dated 2025-11-25, but we'll get to that at the end 🎀). It's short, it's sweet, it's literally one socket option. Let's go. ✨

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🌸 LIBRARY 🌸

Standard C library (libc, -lc). Yeah girl, you already linked it. 💅

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🦋 SYNOPSIS 🦋

#include <netinet/in.h>  /* Definition of IP* constants */
#include <sys/socket.h>

int getsockopt(int sockfd, IPPROTO_IP, IP_MTU,
               int *val, sizeof(int));

not me putting the includes in the code block exactly how they are, because that comment /* Definition of IP* constants */ is doing the lord's work and I will NOT be paraphrasing it 🙈

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✨ DESCRIPTION ✨

So basically: you're retrieving the current known path MTU of the current socket. That's it. That's the whole vibe. MTU = maximum transmission unit = how big a packet can be before it gets real rude about it. 💀

Quick vibe check on the rules though, because there are two and they are not negotiable:

• IP_MTU is valid only for getsockopt(2). It is not a setsockopt girlie. Don't try it.
• It can be employed only when the socket has been connected. No connection, no MTU. That's the law. 👑

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🌈 ERRORS 🌈

Not gonna reinvent the wheel here, bestie — go read the real ones:

• See IPPROTO_IP(2const).
• See getsockopt(2).
• See ip(7).

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⭐ STANDARDS ⭐

Linux. Just Linux. That's the one. 🐧

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🎀 HISTORY 🎀

Linux 2.2. — she's old, she's established, she's an icon and she's been an icon. periodt.

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💜 SEE ALSO 💜

• IPPROTO_IP(2const)
• getsockopt(2)
• ip(7)

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and that's the whole page, bestie — go forth and size your MTU responsibly 🫶✨

signing off with the receipts: this was the Linux man-pages 6.20 release, page dated 2025-11-25. love u, byeee 💅🌸