link — make a new name for a file
#include <unistd.h>
int
link( |
const char * | oldpath, |
| const char * | newpath); |
link() creates a new link
(also known as a hard link) to an existing file.
If newpath exists
it will not be
overwritten.
This new name may be used exactly as the old one for any operation; both names refer to the same file (and so have the same permissions and ownership) and it is impossible to tell which name was the "original".
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
Write access to the directory containing newpath is denied, or
search permission is denied for one of the directories
in the path prefix of oldpath or newpath. (See also
path_resolution(7).)
newpath
already exists.
oldpath or
newpath points
outside your accessible address space.
An I/O error occurred.
Too many symbolic links were encountered in
resolving oldpath or newpath.
The file referred to by oldpath already has the
maximum number of links to it.
oldpath or
newpath was too
long.
A directory component in oldpath or newpath does not exist or
is a dangling symbolic link.
Insufficient kernel memory was available.
The device containing the file has no room for the new directory entry.
A component used as a directory in oldpath or newpath is not, in fact,
a directory.
oldpath is a
directory.
The filesystem containing oldpath and newpath does not support
the creation of hard links.
The file is on a read-only filesystem.
oldpath and
newpath are not
on the same mounted filesystem. (Linux permits a
filesystem to be mounted at multiple points, but
link() does not work
across different mount points, even if the same
filesystem is mounted on both.)
Hard links, as created by link(), cannot span filesystems. Use
symlink(2) if this is
required.
POSIX.1-2001 says that link() should dereference oldpath if it is a symbolic
link. However, Linux does not do so: if oldpath is a symbolic link,
then newpath is
created as a (hard) link to the same symbolic link file
(i.e., newpath
becomes a symbolic link to the same file that oldpath refers to). Some other
implementations behave in the same manner as Linux.
On NFS file systems, the return code may be wrong in case the NFS server performs the link creation and dies before it can say so. Use stat(2) to find out if the link got created.