man2/link.2

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.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
.\"                               1993 Michael Haardt, Ian Jackson.
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.\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1994-08-21 by Michael Haardt
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Modified 2005-04-04, as per suggestion by Michael Hardt for rename.2
.\"
.TH LINK 2 2012-10-16 "Linux" "Linux Programmer's Manual"
.SH NAME
link \- make a new name for a file
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int link(const char *" oldpath ", const char *" newpath );
.SH DESCRIPTION
.BR link ()
creates a new link (also known as a hard link) to an existing file.

If
.I newpath
exists it will
.I 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".
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
Write access to the directory containing
.I newpath
is denied, or search permission is denied for one of the directories
in the path prefix of
.I oldpath
or
.IR newpath .
(See also
.BR path_resolution (7).)
.TP
.B EDQUOT
The user's quota of disk blocks on the file system has been exhausted.
.TP
.B EEXIST
.I newpath
already exists.
.TP
.B EFAULT
.IR oldpath " or " newpath " points outside your accessible address space."
.TP
.B EIO
An I/O error occurred.
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
.IR oldpath " or " newpath .
.TP
.B EMLINK
The file referred to by
.I oldpath
already has the maximum number of links to it.
.TP
.B ENAMETOOLONG
.IR oldpath " or " newpath " was too long."
.TP
.B ENOENT
A directory component in
.IR oldpath " or " newpath
does not exist or is a dangling symbolic link.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOSPC
The device containing the file has no room for the new directory
entry.
.TP
.B ENOTDIR
A component used as a directory in
.IR oldpath " or " newpath
is not, in fact, a directory.
.TP
.B EPERM
.I oldpath
is a directory.
.TP
.B EPERM
The file system containing
.IR oldpath " and " newpath
does not support the creation of hard links.
.TP
.BR EPERM " (since Linux 3.6)"
The caller does not have permission to create a hard link to this file
(see the description of
.IR /proc/sys/fs/protected_hardlink
in
.BR proc (5)).
.TP
.B EROFS
The file is on a read-only file system.
.TP
.B EXDEV
.IR oldpath " and " newpath
are not on the same mounted file system.
(Linux permits a file system to be mounted at multiple points, but
.BR link ()
does not work across different mount points,
even if the same file system is mounted on both.)
.SH "CONFORMING TO"
SVr4, 4.3BSD, POSIX.1-2001 (but see NOTES).
.\" SVr4 documents additional ENOLINK and
.\" EMULTIHOP error conditions; POSIX.1 does not document ELOOP.
.\" X/OPEN does not document EFAULT, ENOMEM or EIO.
.SH NOTES
Hard links, as created by
.BR link (),
cannot span file systems.
Use
.BR symlink (2)
if this is required.

POSIX.1-2001 says that
.BR link ()
should dereference
.I oldpath
if it is a symbolic link.
However, since kernel 2.0,
.\" more precisely: since kernel 1.3.56
Linux does not do so: if
.I oldpath
is a symbolic link, then
.I newpath
is created as a (hard) link to the same symbolic link file
(i.e.,
.I newpath
becomes a symbolic link to the same file that
.I oldpath
refers to).
Some other implementations behave in the same manner as Linux.
.\" For example, the default Solaris compilation environment
.\" behaves like Linux, and contributors to a March 2005
.\" thread in the Austin mailing list reported that some
.\" other (System V) implementations did/do the same -- MTK, Apr 05
POSIX.1-2008 changes the specification of
.BR link (),
making it implementation-dependent whether or not
.I oldpath
is dereferenced if it is a symbolic link.
For precise control over the treatment of symbolic links when
creating a link, see
.BR linkat (2).
.SH BUGS
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
.BR stat (2)
to find out if the link got created.
.SH "SEE ALSO"
.BR ln (1),
.BR linkat (2),
.BR open (2),
.BR rename (2),
.BR stat (2),
.BR symlink (2),
.BR unlink (2),
.BR path_resolution (7),
.BR symlink (7)