OPENAT(2)						     Linux Programmer's Manual							 OPENAT(2)

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  applica-
       tion.  (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/.

Linux								    2009-12-13								 OPENAT(2)