| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
OPENAT(2) Linux Programmer's Manual OPENAT(2)
openat - open a file relative to a directory file descriptor
#include <fcntl.h>
int openat(int dirfd, const char *pathname, int flags);
int openat(int dirfd, const char *pathname, int flags, mode_t mode);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
openat():
Since glibc 2.10:
_XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_ATFILE_SOURCE
The openat() system call operates in exactly the same way as open(2),
except for the differences described in this manual page.
If the pathname given in pathname is relative, then it is interpreted
relative to the directory referred to by the file descriptor dirfd (rather
than relative to the current working directory of the calling process, as
is done by open(2) for a relative pathname).
If pathname is relative and dirfd is the special value AT_FDCWD, then
pathname is interpreted relative to the current working directory of the
calling process (like open(2)).
If pathname is absolute, then dirfd is ignored.
On success, openat() returns a new file descriptor. On error, -1 is
returned and errno is set to indicate the error.
The same errors that occur for open(2) can also occur for openat(). The
following additional errors can occur for openat():
EBADF dirfd is not a valid file descriptor.
ENOTDIR
pathname is relative and dirfd is a file descriptor referring to a
file other than a directory.
openat() was added to Linux in kernel 2.6.16; library support was added to
glibc in version 2.4.
POSIX.1-2008. A similar system call exists on Solaris.
openat() and other similar system calls suffixed "at" are supported for two
reasons.
First, openat() allows an application to avoid race conditions that could
occur when using open(2) to open files in directories other than the
current working directory. These race conditions result from the fact that
some component of the directory prefix given to open(2) could be changed in
parallel with the call to open(2). Such races can be avoided by opening a
file descriptor for the target directory, and then specifying that file
descriptor as the dirfd argument of openat().
Second, openat() allows the implementation of a per-thread "current working
directory", via file descriptor(s) maintained by the application. (This
functionality can also be obtained by tricks based on the use of
/proc/self/fd/dirfd, but less efficiently.)
faccessat(2), fchmodat(2), fchownat(2), fstatat(2), futimesat(2),
linkat(2), mkdirat(2), mknodat(2), open(2), readlinkat(2), renameat(2),
symlinkat(2), unlinkat(2), utimensat(2), mkfifoat(3), path_resolution(7)
This page is part of release 3.41 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be
found at http://www.kernel.org/doc/man-pages/.
Linux 2012-05-04 OPENAT(2)
HTML rendering created 2012-05-11 by Michael Kerrisk,
author of
The Linux Programming Interface,
maintainer of the
Linux man-pages project