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 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 3.54 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/.