getuid(2)

💖 getuid — bestie, let's talk about who you are 💖

okay so this page is getuid(2) from the System Calls Manual, and it's literally the "who am I" of Unix 🪞 no cap, it's a whole vibe check for your process's identity.

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✨ NAME ✨

getuid, geteuid — get user identity 🫶

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📚 LIBRARY 📚

Standard C library — that's libc, and you link it with -lc like always 💅

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🌸 SYNOPSIS 🌸

#include <unistd.h>

uid_t getuid(void);
uid_t geteuid(void);

two lil functions, zero arguments, both handing you back a uid_t. iconic behavior honestly 🎀

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🦋 DESCRIPTION 🦋

so like. every process has identities ok and these two functions are how you peek at them 👀

• getuid() — returns the real user ID of the calling process 🫶
• geteuid() — returns the effective user ID of the calling process ✨

that's it. that's the whole function. it's giving "short and sweet and ate" 💖

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💀 ERRORS 💀

bestie these functions are literally always successful. always. never once have they failed and they never modify errno.

no error codes, no drama, no 3am debugging. it's the one syscall that would never do you dirty 😭🫶

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👑 STANDARDS 👑

POSIX.1-2024 — certified, standardized, fully that girl 💅

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🌈 HISTORY 🌈

storytime, sit down 🧚

• 4.3BSD, and POSIX.1-1988 — that's where this all comes from 📜
• in UNIX V6 the getuid() call was a whole combo deal: it returned (euid << 8) + uid 😳 both IDs crammed into one value, wild
• then UNIX V7 said "no actually" and introduced the separate calls getuid() and geteuid() 🎀 and that's the version we still vibe with
• the original Linux getuid() and geteuid() system calls only supported 16-bit user IDs 🙈
• after that, Linux 2.4 added getuid32() and geteuid32(), which support 32-bit IDs 🔥 glow-up fr fr
• the glibc getuid() and geteuid() wrapper functions transparently deal with all those variations across kernel versions — so you don't have to think about it, you just get your answer 💖
• special case alert 🚨 on Alpha, instead of a pair of getuid() and geteuid() system calls, there's a single getxuid() system call that returns a pair of real and effective UIDs
• and yep, the glibc getuid() and geteuid() wrappers transparently deal with that too 🫶
• if you wanna get into the register mapping details for that, go see syscall(2) 👑

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🔍 SEE ALSO 🔍

• getresuid(2)
• setreuid(2)
• setuid(2)
• credentials(7)

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ok real talk: these are the safest, most well-behaved calls on the whole system. no errno, no failure, no notes. use them and go be your main character self ✨

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and that's the page bestie!! this came from Linux man-pages 6.20, dated 2026-02-08 — mwah, thank u to whoever maintains these, we love u 💖🎀🦋 periodt 💅