LINKAT(2)

NAME
linkat - create a file link relative to directory file descriptors

SYNOPSIS
#include <fcntl.h> /* Definition of AT_* constants */
#include <unistd.h>

int linkat(int olddirfd, const char *oldpath,
           int newdirfd, const char *newpath, int flags);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

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

DESCRIPTION
The linkat() system call operates in exactly the same way as link(2), except for the differences described in this manual page. If the pathname given in oldpath is relative, then it is interpreted relative to the directory referred to by the file descriptor olddirfd (rather than relative to the current working directory of the calling process, as is done by link(2) for a relative pathname). If oldpath is relative and olddirfd is the special value AT_FDCWD, then oldpath is interpreted relative to the current working directory of the calling process (like link(2)). If oldpath is absolute, then olddirfd is ignored. The interpretation of newpath is as for oldpath, except that a relative pathname is interpreted relative to the directory referred to by the file descriptor newdirfd. The following values can be bitwise ORed in flags:

AT_EMPTY_PATH (since Linux 2.6.39)
    If oldpath is an empty string, create a link to the file referenced by olddirfd (which may have been obtained using the open(2) O_PATH flag). In this case, olddirfd can refer to any type of file, not just a directory. The caller must have the CAP_DAC_READ_SEARCH capability in order to use this flag; this prevents arbitrary users from creating hard links using file descriptors received via a UNIX domain socket (see the discussion of SCM_RIGHTS in unix(7)).

AT_SYMLINK_FOLLOW (since Linux 2.6.18)
    By default, linkat(), does not dereference oldpath if it is a symbolic link (like link(2)). The flag AT_SYMLINK_FOLLOW can be specified in flags to cause oldpath to be dereferenced if it is a symbolic link.

Before kernel 2.6.18, the flags argument was unused, and had to be specified as 0.

RETURN VALUE
On success, linkat() returns 0. On error, -1 is returned and errno is set to indicate the error.

ERRORS
The same errors that occur for link(2) can also occur for linkat(). The following additional errors can occur for linkat():

EBADF
    olddirfd or newdirfd is not a valid file descriptor.

EINVAL
    An invalid flag value was specified in flags.

ENOENT
    AT_EMPTY_PATH was specified in flags, but the caller did not have the CAP_DAC_READ_SEARCH capability.

ENOENT
    An attempt was made to link to the /proc/self/fd/NN file corresponding to a file descriptor created with
        open(path, O_TMPFILE | O_EXCL, mode); See open(2).

ENOTDIR
    oldpath is relative and olddirfd is a file descriptor referring to a file other than a directory; or similar for newpath and newdirfd

VERSIONS
linkat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.

CONFORMING TO
POSIX.1-2008.

NOTES
See openat(2) for an explanation of the need for linkat().

SEE ALSO
link(2), openat(2), path_resolution(7), symlink(7)

COLOPHON
This page is part of release 3.58 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/.