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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

       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.

              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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2008-08-21                         OPENAT(2)