getdtablesize(3) — Linux manual page

getdtablesize(3)         Library Functions Manual        getdtablesize(3)

NAME         top

       getdtablesize - get file descriptor table size

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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         top

       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         top

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

ERRORS         top

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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                            │ Attribute     │ Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │ getdtablesize()                      │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

VERSIONS         top

       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         top

       None.

HISTORY         top

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

SEE ALSO         top

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

COLOPHON         top

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Linux man-pages 6.15            2025-05-17               getdtablesize(3)

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