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OPENAT
Section: Linux Programmer's Manual (2)
Updated: 2009-12-13
Index
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NAME
openat - open a file relative to a directory file descriptor
SYNOPSIS
#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
DESCRIPTION
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.
RETURN VALUE
On success,
openat()
returns a new file descriptor.
On error, -1 is returned and
errno
is set to indicate the error.
ERRORS
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.
VERSIONS
openat()
was added to Linux in kernel 2.6.16.
CONFORMING TO
POSIX.1-2008.
A similar system call exists on Solaris.
NOTES
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.)
SEE ALSO
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)
COLOPHON
This page is part of release 3.27 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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