uname(2)

💖 uname(2) — the manual page, but make it cute ✨

okay bestie, welcome to uname(2), a classic from the System Calls Manual. she gets you the name and info about the kernel you're currently running on, no cap 💅

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🌸 NAME 🌸

uname — get name and information about current kernel

📚 LIBRARY 📚

Standard C library (libc, -lc) 🫶

✨ SYNOPSIS ✨

#include <sys/utsname.h>

int uname(struct utsname *buf);

🦋 DESCRIPTION 🦋

so uname() hands you back all the system info, and it puts it in the structure that buf is pointing at. and the utsname struct lives in <sys/utsname.h>, and she looks like this:

struct utsname {
    char sysname[];    /* Operating system name (e.g., "Linux") */
    char nodename[];   /* Name within communications network
                          to which the node is attached, if any */
    char release[];    /* Operating system release
                          (e.g., "2.6.28") */
    char version[];    /* Operating system version */
    char machine[];    /* Hardware type identifier */
#ifdef _GNU_SOURCE
    char domainname[]; /* NIS or YP domain name */
#endif
};

okay important thing, bestie: the length of those arrays in a struct utsname is unspecified (peep VERSIONS and HISTORY if you wanna know more), and every field is terminated by a null byte ('\0'). periodt. 🎀

💫 RETURN VALUE 💫

slay on success: she returns zero. 😌

but on error, she returns -1, and errno gets set so you know what went wrong. 💀

🙈 ERRORS 🙈

• EFAULT — buf is not valid. like, not valid valid.

👑 VERSIONS 👑

the domainname member (aka the NIS or YP domain name) is a GNU extension, so don't be shocked when other vibes don't have her.

and the length of the fields in the struct? it varies. some operating systems or libraries hardcode a 9 or 33 or 65 or 257. others use SYS_NMLN or _SYS_NMLN or UTSLEN or _UTSNAME_LENGTH. and clearly, using any of those constants is a bad idea — it's giving chaos — so just use sizeof(...) and move on. 🧚

SVr4 uses 257, "to support Internet hostnames" — and that's the largest value you're likely to encounter in the wild — no fr.

🌈 STANDARDS 🌈

POSIX.1-2024. iconic.

📜 HISTORY 📜

POSIX.1-2001, SVr4, 4.4BSD. the lore goes back bestie.

🧵 C library/kernel differences 🧵

over time the utsname structure kept getting bigger, and that led to three successive versions of uname():

• sys_olduname() (slot __NR_oldolduname)
• sys_uname() (slot __NR_olduname)
• sys_newuname() (slot __NR_uname)

the first one used length 9 for all fields. the second used 65. the third also uses 65 but adds the domainname field. and the glibc uname() wrapper function hides all of this from applications — she just invokes the most recent version of the system call that the kernel provides. she's the main character, handling it for you 💅

📝 NOTES 📝

the kernel has the name, release, version, and supported machine type built in. but flip side: the nodename field is configured by the administrator to match the network — this is what BSD historically calls the "hostname", and it's set via sethostname(2). similarly, the domainname field is set via setdomainname(2). 🫶

part of the utsname info is also accessible via /proc/sys/kernel/{ostype, hostname, osrelease, version, domainname}. iykyk.

🎀 SEE ALSO 🎀

• uname(1)
• getdomainname(2)
• gethostname(2)
• uts_namespaces(7)

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heads up bestie, EFAULT means buf isn't valid, and the array lengths are unspecified so please please please use sizeof(...). not a vibe-killer, just a vibe-protector. 🍓

and that's the whole page!! brought to you by Linux man-pages 6.20, dated 2026-02-08. go run uname -a and feel something. mwah 💖✨