getdtablesize(3)           Library Functions Manual           getdtablesize(3)

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 (see feature_test_macros(7)):

       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

DESCRIPTION
       getdtablesize() returns the maximum number of files a process can have
       open, one more than the largest possible value for a file descriptor.

RETURN VALUE
       The current limit on the number of open files per process.

ERRORS
       On Linux, getdtablesize() can return any of the errors described for
       getrlimit(2); see VERSIONS below.

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

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |getdtablesize ()                            | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
VERSIONS
       The glibc version of getdtablesize() calls getrlimit(2) and returns the
       current RLIMIT_NOFILE limit, or OPEN_MAX when that fails.

       Portable applications should employ sysconf(_SC_OPEN_MAX) instead of
       this call.

STANDARDS
       None.

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

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

Linux man-pages 6.19              2026-02-08                  getdtablesize(3)