getdtablesize(3)

✨ getdtablesize(3) ✨

okay bestie, this is getdtablesize from the Library Functions Manual, and honestly? she's a little vintage, a little overlooked, and lowkey kinda iconic. let's get into it 💅

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🌸 NAME 🌸

getdtablesize — get file descriptor table size

📚 LIBRARY 📚

Standard C library (libc, -lc) 🫶

🎀 SYNOPSIS 🎀

#include <unistd.h>

int getdtablesize(void);

🦋 Feature Test Macro Requirements for glibc

(psst — see feature_test_macros(7) for the full tea 👀)

getdtablesize():

• Since glibc 2.20:
  • _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
• glibc 2.12 to glibc 2.19:
  • _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
• Before glibc 2.12:
  • _BSD_SOURCE || _XOPEN_SOURCE >= 500

like… the macro requirements genuinely have lore. they evolve. they grow. they went through eras. 🧚

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💖 DESCRIPTION 💖

getdtablesize() returns the maximum number of files a process can have open — which is exactly one more than the largest possible value for a file descriptor. so if your biggest fd number is n, the answer is n + 1. it's giving "one extra seat at the table just in case." 🍓

🌈 RETURN VALUE 🌈

The current limit on the number of open files per process. that's your number. that's the vibe check result. ✨

💀 ERRORS 💀

On Linux, getdtablesize() can return any of the errors described for getrlimit(2) — head down to VERSIONS below for why that's even a thing 👇

👑 ATTRIBUTES 👑

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

• getdtablesize() — Thread safety: MT-Safe

(no cap, she's MT-Safe, we love a thread-safe queen 🫶)

🎀 VERSIONS 🎀

The glibc version of getdtablesize() calls getrlimit(2) and returns the current RLIMIT_NOFILE limit, or OPEN_MAX when that fails.

⚠️ okay so real talk: portable applications should employ sysconf(_SC_OPEN_MAX) instead of this call. she's cute but she's not the one to take on the road trip. 😭

⭐ STANDARDS ⭐

None.

(yeah. none. she's not standardized bestie. she's just there, doing her thing, living her truth. 💅)

🦋 HISTORY 🦋

SVr4, 4.4BSD (first appeared in 4.2BSD).

absolute OG behavior, first appeared in 4.2BSD — not me getting emotional about a libc function 🥹

🌸 SEE ALSO 🌸

close(2), dup(2), getrlimit(2), open(2)

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and that's the whole page, bestie!! go forth and count your file descriptors responsibly 💜

mwah 💋 — this was getdtablesize(3) from Linux man-pages 6.20, dated 2026-02-08. periodt. ✨👑