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       openat - open a file relative to a directory file descriptor


       #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)):

       Since glibc 2.10: _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
       Before glibc 2.10: _ATFILE_SOURCE


       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 error.


       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),


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       be found at