ether_aton(3)

✨ ether_aton(3) ✨

okay bestie so you're in the Library Functions Manual and the page is called ether_aton(3), and it's literally all about Ethernet address manipulation routines. like the whole little family of them. come sit with me 💖

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🎀 NAME 🎀

ether_aton, ether_ntoa, ether_ntohost, ether_hostton, ether_line, ether_ntoa_r, ether_aton_r — Ethernet address manipulation routines

no cap, that's the whole squad. seven whole functions. iconic behavior honestly.

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📚 LIBRARY 📚

Standard C library (libc, -lc)

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🦋 SYNOPSIS 🦋

#include <netinet/ether.h>

char *ether_ntoa(const struct ether_addr *addr);
struct ether_addr *ether_aton(const char *asc);

int ether_ntohost(char *hostname, const struct ether_addr *addr);
int ether_hostton(const char *hostname, struct ether_addr *addr);

int ether_line(const char *line, struct ether_addr *addr,
               char *hostname);

/* GNU extensions */
char *ether_ntoa_r(const struct ether_addr *addr, char *buf);

struct ether_addr *ether_aton_r(const char *asc,
                                struct ether_addr *addr);

see those last two? GNU extensions. special little bonus girls ✨

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💅 DESCRIPTION 💅

ether_aton() takes the 48-bit Ethernet host address asc, which is written in the standard hex-digits-and-colons notation, and converts it into binary data in network byte order. it hands you back a pointer to it in a statically allocated buffer, which means the very next call lowkey overwrites it. so don't get attached 😭. and if the address is invalid, ether_aton() returns NULL. no address for you bestie.

ether_ntoa() goes the other way — it takes the Ethernet host address addr in network byte order and converts it to a string in standard hex-digits-and-colons notation, and it omits leading zeros (skinny legend). the string comes back in a statically allocated buffer, which again means subsequent calls will overwrite it. it's giving "borrowed and reused".

ether_ntohost() maps an Ethernet address to the corresponding hostname in /etc/ethers, and returns nonzero if it cannot be found.

ether_hostton() maps a hostname to the corresponding Ethernet address in /etc/ethers, and returns nonzero if it cannot be found. yes they're basically each other's mirror selfies 🪞

ether_line() parses a line in /etc/ethers format and returns an address and hostname pair, or nonzero if it cannot be parsed. the format is: ethernet address, then whitespace, then hostname — and a '#' introduces a comment. and listen, important detail: the buffer pointed to by hostname must be sufficiently long — like, for example, have the same length as line. do not skimp on it, she needs room to breathe 🌸

ether_ntoa_r() and ether_aton_r() are reentrant thread-safe versions of ether_ntoa() and ether_aton() respectively, and they do not use static buffers. the upgrade era fr fr 👑

so the structure ether_addr is defined in <net/ethernet.h> as:

struct ether_addr {
    uint8_t ether_addr_octet[6];
}

six octets of pure main character energy 🫶

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🔥 ATTRIBUTES 🔥

for an explanation of the terms used in this section, see attributes(7).

• ether_aton(), ether_ntoa() — Thread safety: MT-Unsafe
• ether_ntohost(), ether_hostton(), ether_line(), ether_ntoa_r(), ether_aton_r() — Thread safety: MT-Safe

so the first two are the chaotic ones (no shared-buffer safety bestie, that static buffer is a group chat everyone's typing in 💀) and the rest are the well-behaved thread-safe girlies ✨

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⭐ STANDARDS ⭐

None. literally none. not a single standard. she's free-spirited like that 🙈

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🌈 HISTORY 🌈

4.3BSD, SunOS.

old money. vintage. we love a classic 💜

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💀 BUGS 💀

so in glibc 2.2.5 and earlier, the implementation of ether_line() is broken. that's it, that's the bug notice. if you're on something that ancient, godspeed bestie 🕯️

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🧚 SEE ALSO 🧚

ethers(5)

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okay and one last vibe check: those static-buffer functions (ether_aton(), ether_ntoa()) will overwrite what they gave you on the next call, so if you're doing threads, reach for the _r versions. no cap, it's literally the whole point of them 💖

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that's the whole page, bestie — sent to you with love from the Linux man-pages 6.20, dated 2026-02-08, and it's ether_aton(3) forever and always 🎀💅✨