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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; library support was added
       to glibc in version 2.4.
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_resolu-
       tion(7)
COLOPHON
       This page is part of release 3.53 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)