In POSIX systems, one file can have many names at the same time. All of
the names are equally real, and no one of them is preferred to the
others.
To add a name to a file, use the link function. (The new name is
also called a hard link to the file.) Creating a new link to a
file does not copy the contents of the file; it simply makes a new name
by which the file can be known, in addition to the file's existing name
or names.
One file can have names in several directories, so the organization
of the file system is not a strict hierarchy or tree.
In most implementations, it is not possible to have hard links to the
same file in multiple file systems. link reports an error if you
try to make a hard link to the file from another file system when this
cannot be done.
The prototype for the link function is declared in the header
file unistd.h.
— Function: int link (const char *oldname, const char *newname)
The link function makes a new link to the existing file named by
oldname, under the new name newname.
This function returns a value of 0 if it is successful and
-1 on failure. In addition to the usual file name errors
(see File Name Errors) for both oldname and newname, the
following errno error conditions are defined for this function:
EACCES
You are not allowed to write to the directory in which the new link is
to be written.
EEXIST
There is already a file named newname. If you want to replace
this link with a new link, you must remove the old link explicitly first.
EMLINK
There are already too many links to the file named by oldname.
(The maximum number of links to a file is LINK_MAX; see
Limits for Files.)
ENOENT
The file named by oldname doesn't exist. You can't make a link to
a file that doesn't exist.
ENOSPC
The directory or file system that would contain the new link is full
and cannot be extended.
EPERM
In the GNU system and some others, you cannot make links to directories.
Many systems allow only privileged users to do so. This error
is used to report the problem.
EROFS
The directory containing the new link can't be modified because it's on
a read-only file system.
EXDEV
The directory specified in newname is on a different file system
than the existing file.
EIO
A hardware error occurred while trying to read or write the to filesystem.
Published under the terms of the GNU General Public License
