ulimit(3)

💅 ulimit(3) — the library call, not the shell thing, bestie

okay so real talk: this is ulimit(3), a library function from the Library Functions Manual, living in the Standard C library (libc, link it with -lc). It gets and sets user limits. And um. She's ✨obsolete✨. But we're still gonna learn her, because history is iconic and also she shows up in old code like a ghost at the function party 🫶

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✨ NAME ✨

ulimit — get and set user limits 💖

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📚 LIBRARY 📚

Standard C library, aka libc, aka link with -lc.

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🎀 SYNOPSIS 🎀

#include <ulimit.h>

[[deprecated]] long ulimit(int cmd, long newlimit);

she is literally marked [[deprecated]] in the header, the compiler is gonna side-eye you 😭

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🦋 DESCRIPTION 🦋

⚠️ Warning: this routine is obsolete. Use getrlimit(2), setrlimit(2), and sysconf(3) instead. And if you want the shell command ulimit, go see bash(1) — totally different girl, same name.

So the ulimit() call gets or sets some limit for the calling process. Which limit? Depends on cmd, bestie. Here are the values:

• UL_GETFSIZE — returns the limit on the size of a file, measured in units of 512 bytes 🗂️
• UL_SETFSIZE — sets the limit on the size of a file ✍️
• 3 — (not implemented for Linux, sorry!! 🙈) returns the maximum possible address of the data segment
• 4 — (implemented, but no symbolic constant was provided, the disrespect 💀) returns the maximum number of files that the calling process can open

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🔥 RETURN VALUE 🔥

On success, ulimit() returns a nonnegative value ✨

On error, it returns -1, and errno gets set to tell you what went wrong. main character error reporting, honestly.

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😭 ERRORS 😭

• EPERM — an unprivileged process tried to increase a limit. babe you do not have the clearance for that 🚫

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👑 ATTRIBUTES 👑

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

• Interface: ulimit()
• Attribute: Thread safety
• Value: MT-Safe 🧵✅

(She's thread-safe, at least. Obsessed.)

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⭐ STANDARDS ⭐

POSIX.1-2008.

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🌸 HISTORY 🌸

• SVr4, POSIX.1-2001
• POSIX.1-2008 marks it as obsolete 🪦

so yeah, she's a legacy legend. we stan a retired icon but we do not call her in new code, periodt.

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🌈 SEE ALSO 🌈

• bash(1)
• getrlimit(2)
• setrlimit(2)
• sysconf(3)

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and that's the whole vibe check 💖 slay, go use getrlimit(2) instead, ily, bye 🫶✨

This page is from Linux man-pages 6.20, dated 2026-02-08 — mwah, kiss the maintainers, they're doing the lord's work 🎀