IP_RECVERR(2const)

✨ IP_RECVERR 💖 (a 2const girlie, from the Linux man-pages)

okay so bestie, welcome to the extended reliable error message passing page 🎀 — it lives in the IP_RECVERR constant, and it's giving "your datagram socket finally tells you the truth" energy.

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📚 LIBRARY

Standard C library (libc, -lc) 🫶

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🌸 SYNOPSIS

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

int setsockopt(int sockfd, IPPROTO_IP, IP_RECVERR,
               const int *enable, sizeof(int));
int getsockopt(int sockfd, IPPROTO_IP, IP_RECVERR,
               int *enabled, sizeof(int));

struct sock_extended_err {
    uint32_t  ee_errno;   /* error number */
    uint8_t   ee_origin;  /* where the error originated */
    uint8_t   ee_type;    /* type */
    uint8_t   ee_code;    /* code */
    uint8_t   ee_pad;
    uint32_t  ee_info;    /* additional information */
    uint32_t  ee_data;    /* other data */
    /* More data may follow */
};

#define SO_EE_ORIGIN_NONE    0
#define SO_EE_ORIGIN_LOCAL   1
#define SO_EE_ORIGIN_ICMP    2
#define SO_EE_ORIGIN_ICMP6   3

struct sockaddr *SO_EE_OFFENDER(struct sock_extended_err *);

no cap, that struct is literally the whole plot of this page. 💅

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👑 DESCRIPTION

So like — this flag turns on extended reliable error message passing. And the default? Disabled. 🙈 (she's shy at first, understandable.)

When you enable it on a datagram socket, all the errors that get generated will be queued up in a per-socket error queue. Then, when you receive an error from a socket operation, you can go get those errors by calling recvmsg(2) with the MSG_ERRQUEUE flag set. 🌈

The sock_extended_err structure that describes the error gets passed in an ancillary message with the type IP_RECVERR and the level IPPROTO_IP. This is genuinely so useful for reliable error handling on unconnected sockets, fr fr. And the received data portion of the error queue? That contains the error packet. 💖

The IP_RECVERR control message contains a sock_extended_err structure.

• .ee_errno — contains the errno number of the queued error. 😭
• .ee_origin — is the origin code of where the error originated. 🦋

The other fields are protocol-specific, iykyk.

The macro SO_EE_OFFENDER() returns a pointer to the address of the network object where the error originated from, given a pointer to the ancillary message. And if that address isn't known? Then the .sa_family member of the sockaddr contains AF_UNSPEC, and the other fields of the sockaddr are undefined. 💀 (undefined behaviour, we do not romanticize her.)

IP uses the sock_extended_err structure as follows:

• .ee_origin is set to SO_EE_ORIGIN_ICMP for errors received as an ICMP packet, or SO_EE_ORIGIN_LOCAL for locally generated errors. Unknown values should be ignored. periodt.
• .ee_type and .ee_code are set from the type and code fields of the ICMP header. ✨
• .ee_info contains the discovered MTU for EMSGSIZE errors. 👑
• The message also contains the sockaddr_in of the node caused that the error, which can be accessed with the SO_EE_OFFENDER() macro.

The .sin_family field of the SO_EE_OFFENDER() address is AF_UNSPEC when the source was unknown. When the error originated from the network, all IP options (IP_OPTIONS(2const), IP_TTL(2const), etc.) enabled on the socket and contained in the error packet are passed as control messages. And the payload of the packet causing the error is returned as normal payload. 🍓

ok bestie important one: TCP has no error queue. MSG_ERRQUEUE is not permitted on SOCK_STREAM sockets. IP_RECVERR is valid for TCP, but all errors are returned by socket function return or SO_ERROR only. 😤

For raw sockets, IP_RECVERR enables passing of all received ICMP errors to the application — otherwise errors are reported only on connected sockets. 🧚

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💀 ERRORS

See IPPROTO_IP(2const). See setsockopt(2). See ip(7). 💜

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⭐ STANDARDS

Linux. that's it, that's the standards section, she's a Linux exclusive 💅

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🎀 HISTORY

Linux 2.2. vintage but still iconic, no notes. 🔥

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🦋 SEE ALSO

IPPROTO_IP(2const), setsockopt(2), ip(7)

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and that's the whole page, bestie!! 🌸

this was pulled straight from Linux man-pages 6.20, dated 2025-11-25 — mwah, go enable your error queue and slay 💖✨👑