NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON
OPENAT(2) Linux Programmer's Manual OPENAT(2)
openat - open a file relative to a directory file descriptor
#define _ATFILE_SOURCE
#include <fcntl.h>
int openat(int dirfd, const char *pathname, int flags);
int openat(int dirfd, const char *pathname, int flags, mode_t mode);
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.
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 3.08 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 2008-08-21 OPENAT(2)