#define _ATFILE_SOURCE
#include <fcntl.h> /* Definition of AT_* constants */
#include <unistd.h>
int linkat(int olddirfd, const char *oldpath,
int newdirfd, const char *newpath, int flags);
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.
By default, linkat(), does not dereference oldpath if it is a symbolic link (like link(2)). Since Linux 2.6.18, 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.