openat man page

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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);

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  the pathname given in 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 the pathname given in 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  a  relative  path  and  dirfd is a file descriptor
              referring to a file other than a directory.

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()  could
       be  changed  in  parallel  with  the call to open().  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.)

CONFORMING TO

       This system call is non-standard but is proposed  for  inclusion  in  a
       future revision of POSIX.1.  A similar system call exists on Solaris.

VERSIONS

       openat() was added to Linux in kernel 2.6.16.

SEE ALSO

       mkdirat(2), mknodat(2), open(2), path_resolution(2), mkfifoat(3).



Linux 2.6.16                      2006-03-06                         OPENAT(2)

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