getdtablesize — get file descriptor table size


#include <unistd.h>

int getdtablesize(void);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):


Since glibc 2.12:
/* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE
    || ! (_POSIX_C_SOURCE >= 200112L)

Before glibc 2.12: _BSD_SOURCE || _XOPEN_SOURCE >= 500


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.


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


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

Interface Attribute Value
getdtablesize() Thread safety MT-Safe

Conforming to

SVr4, 4.4BSD (the getdtablesize() function first appeared in 4.2BSD). It is not specified in POSIX.1; portable applications should employ sysconf(_SC_OPEN_MAX) instead of this call.


getdtablesize() is implemented as a libc library function. The glibc version calls getrlimit(2) and returns the current RLIMIT_NOFILE limit, or OPEN_MAX when that fails.

See Also

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


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

strace(1), syscalls(2).

The man page getdtablesize(2) is an alias of getdtablesize(3).

2016-03-15 Linux Programmer's Manual