1 .\" This manpage is Copyright (C) 1992 Drew Eckhardt;
2 .\" and Copyright (C) 1993 Michael Haardt, Ian Jackson.
3 .\" and Copyright (C) 2006, 2014 Michael Kerrisk
5 .\" %%%LICENSE_START(VERBATIM)
6 .\" Permission is granted to make and distribute verbatim copies of this
7 .\" manual provided the copyright notice and this permission notice are
8 .\" preserved on all copies.
10 .\" Permission is granted to copy and distribute modified versions of this
11 .\" manual under the conditions for verbatim copying, provided that the
12 .\" entire resulting derived work is distributed under the terms of a
13 .\" permission notice identical to this one.
15 .\" Since the Linux kernel and libraries are constantly changing, this
16 .\" manual page may be incorrect or out-of-date. The author(s) assume no
17 .\" responsibility for errors or omissions, or for damages resulting from
18 .\" the use of the information contained herein. The author(s) may not
19 .\" have taken the same level of care in the production of this manual,
20 .\" which is licensed free of charge, as they might when working
23 .\" Formatted or processed versions of this manual, if unaccompanied by
24 .\" the source, must acknowledge the copyright and authors of this work.
27 .\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
28 .\" Modified 1994-08-21 by Michael Haardt
29 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
30 .\" Modified 2005-04-04, as per suggestion by Michael Hardt for rename.2
32 .TH LINK 2 2014-03-19 "Linux" "Linux Programmer's Manual"
34 link, linkat \- make a new name for a file
37 .B #include <unistd.h>
39 .BI "int link(const char *" oldpath ", const char *" newpath );
41 .BR "#include <fcntl.h> " "/* Definition of AT_* constants */"
42 .B #include <unistd.h>
44 .BI "int linkat(int " olddirfd ", const char *" oldpath ,
45 .BI " int " newdirfd ", const char *" newpath ", int " flags );
49 Feature Test Macro Requirements for glibc (see
50 .BR feature_test_macros (7)):
59 _XOPEN_SOURCE\ >=\ 700 || _POSIX_C_SOURCE\ >=\ 200809L
68 creates a new link (also known as a hard link) to an existing file.
76 This new name may be used exactly as the old one for any operation;
77 both names refer to the same file (and so have the same permissions
78 and ownership) and it is impossible to tell which name was the
83 system call operates in exactly the same way as
85 except for the differences described here.
87 If the pathname given in
89 is relative, then it is interpreted relative to the directory
90 referred to by the file descriptor
92 (rather than relative to the current working directory of
93 the calling process, as is done by
95 for a relative pathname).
105 is interpreted relative to the current working
106 directory of the calling process (like
115 The interpretation of
119 except that a relative pathname is interpreted relative
120 to the directory referred to by the file descriptor
123 The following values can be bitwise ORed in
126 .BR AT_EMPTY_PATH " (since Linux 2.6.39)"
127 .\" commit 11a7b371b64ef39fc5fb1b6f2218eef7c4d035e3
130 is an empty string, create a link to the file referenced by
132 (which may have been obtained using the
138 must refer to a file other than a directory.
139 The caller must have the
140 .BR CAP_DAC_READ_SEARCH
141 capability in order to use this flag;
142 this prevents arbitrary users from creating hard links
143 using file descriptors received via a UNIX domain socket
144 (see the discussion of
148 This flag is Linux-specific; define
150 .\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
151 to obtain its definition.
153 .BR AT_SYMLINK_FOLLOW " (since Linux 2.6.18)"
158 if it is a symbolic link (like
166 to be dereferenced if it is a symbolic link.
168 Before kernel 2.6.18, the
170 argument was unused, and had to be specified as 0.
174 for an explanation of the need for
177 On success, zero is returned.
178 On error, \-1 is returned, and
180 is set appropriately.
184 Write access to the directory containing
186 is denied, or search permission is denied for one of the directories
187 in the path prefix of
192 .BR path_resolution (7).)
195 The user's quota of disk blocks on the filesystem has been exhausted.
202 .IR oldpath " or " newpath " points outside your accessible address space."
205 An I/O error occurred.
208 Too many symbolic links were encountered in resolving
209 .IR oldpath " or " newpath .
212 The file referred to by
214 already has the maximum number of links to it.
217 .IR oldpath " or " newpath " was too long."
220 A directory component in
221 .IR oldpath " or " newpath
222 does not exist or is a dangling symbolic link.
225 Insufficient kernel memory was available.
228 The device containing the file has no room for the new directory
232 A component used as a directory in
233 .IR oldpath " or " newpath
234 is not, in fact, a directory.
241 The filesystem containing
242 .IR oldpath " and " newpath
243 does not support the creation of hard links.
245 .BR EPERM " (since Linux 3.6)"
246 The caller does not have permission to create a hard link to this file
247 (see the description of
248 .IR /proc/sys/fs/protected_hardlinks
253 The file is on a read-only filesystem.
256 .IR oldpath " and " newpath
257 are not on the same mounted filesystem.
258 (Linux permits a filesystem to be mounted at multiple points, but
260 does not work across different mount points,
261 even if the same filesystem is mounted on both.)
263 The following additional errors can occur for
270 is not a valid file descriptor.
273 An invalid flag value was specified in
280 but the caller did not have the
281 .B CAP_DAC_READ_SEARCH
285 An attempt was made to link to the
287 file corresponding to a file descriptor created with
289 open(path, O_TMPFILE | O_EXCL, mode);
298 is a file descriptor referring to a file other than a directory;
309 is an empty string, and
311 refers to a directory.
314 was added to Linux in kernel 2.6.16;
315 library support was added to glibc in version 2.4.
318 SVr4, 4.3BSD, POSIX.1-2001 (but see NOTES), POSIX.1-2008.
319 .\" SVr4 documents additional ENOLINK and
320 .\" EMULTIHOP error conditions; POSIX.1 does not document ELOOP.
321 .\" X/OPEN does not document EFAULT, ENOMEM or EIO.
326 Hard links, as created by
328 cannot span filesystems.
333 POSIX.1-2001 says that
337 if it is a symbolic link.
338 However, since kernel 2.0,
339 .\" more precisely: since kernel 1.3.56
340 Linux does not do so: if
342 is a symbolic link, then
344 is created as a (hard) link to the same symbolic link file
347 becomes a symbolic link to the same file that
350 Some other implementations behave in the same manner as Linux.
351 .\" For example, the default Solaris compilation environment
352 .\" behaves like Linux, and contributors to a March 2005
353 .\" thread in the Austin mailing list reported that some
354 .\" other (System V) implementations did/do the same -- MTK, Apr 05
355 POSIX.1-2008 changes the specification of
357 making it implementation-dependent whether or not
359 is dereferenced if it is a symbolic link.
360 For precise control over the treatment of symbolic links when
364 On NFS filesystems, the return code may be wrong in case the NFS server
365 performs the link creation and dies before it can say so.
368 to find out if the link got created.
376 .BR path_resolution (7),
379 This page is part of release 3.64 of the Linux
382 A description of the project,
383 and information about reporting bugs,
385 \%http://www.kernel.org/doc/man\-pages/.