.\" This manpage is Copyright (C) 1992 Drew Eckhardt; .\" and Copyright (C) 1993 Michael Haardt, Ian Jackson. .\" and Copyright (C) 2006, 2014 Michael Kerrisk .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" Modified 1993-07-23 by Rik Faith .\" Modified 1994-08-21 by Michael Haardt .\" Modified 2004-06-23 by Michael Kerrisk .\" Modified 2005-04-04, as per suggestion by Michael Hardt for rename.2 .\" .TH LINK 2 2014-08-19 "Linux" "Linux Programmer's Manual" .SH NAME link, linkat \- make a new name for a file .SH SYNOPSIS .nf .B #include .sp .BI "int link(const char *" oldpath ", const char *" newpath ); .sp .BR "#include " "/* Definition of AT_* constants */" .B #include .sp .BI "int linkat(int " olddirfd ", const char *" oldpath , .BI " int " newdirfd ", const char *" newpath ", int " flags ); .fi .sp .in -4n Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .in .sp .BR linkat (): .PD 0 .ad l .RS 4 .TP 4 Since glibc 2.10: _XOPEN_SOURCE\ >=\ 700 || _POSIX_C_SOURCE\ >=\ 200809L .TP Before glibc 2.10: _ATFILE_SOURCE .RE .ad .PD .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". .SS linkat() The .BR linkat () system call operates in exactly the same way as .BR link (), except for the differences described here. If the pathname given in .I oldpath is relative, then it is interpreted relative to the directory referred to by the file descriptor .I olddirfd (rather than relative to the current working directory of the calling process, as is done by .BR link () for a relative pathname). If .I oldpath is relative and .I olddirfd is the special value .BR AT_FDCWD , then .I oldpath is interpreted relative to the current working directory of the calling process (like .BR link ()). If .I oldpath is absolute, then .I olddirfd is ignored. The interpretation of .I newpath is as for .IR oldpath , except that a relative pathname is interpreted relative to the directory referred to by the file descriptor .IR newdirfd . The following values can be bitwise ORed in .IR flags : .TP .BR AT_EMPTY_PATH " (since Linux 2.6.39)" .\" commit 11a7b371b64ef39fc5fb1b6f2218eef7c4d035e3 If .I oldpath is an empty string, create a link to the file referenced by .IR olddirfd (which may have been obtained using the .BR open (2) .B O_PATH flag). In this case, .I olddirfd can refer to any type of file, not just a directory. This will generally not work if the file has a link count of zero (files created with .BR O_TMPFILE and without .BR O_EXCL are an exception). The caller must have the .BR CAP_DAC_READ_SEARCH capability in order to use this flag. This flag is Linux-specific; define .B _GNU_SOURCE .\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed to obtain its definition. .TP .BR AT_SYMLINK_FOLLOW " (since Linux 2.6.18)" By default, .BR linkat (), does not dereference .I oldpath if it is a symbolic link (like .BR link ()). The flag .B AT_SYMLINK_FOLLOW can be specified in .I flags to cause .I oldpath to be dereferenced if it is a symbolic link. If procfs is mounted, this can be used as an alternative to .BR AT_EMPTY_PATH , like this: .nf .in +4n linkat(AT_FDCWD, "/proc/self/fd/", newdirfd, newname, AT_SYMLINK_FOLLOW); .in .fi .PP Before kernel 2.6.18, the .I flags argument was unused, and had to be specified as 0. .PP See .BR openat (2) for an explanation of the need for .BR linkat (). .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 filesystem 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 filesystem 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_hardlinks in .BR proc (5)). .TP .B EROFS The file is on a read-only filesystem. .TP .B EXDEV .IR oldpath " and " newpath are not on the same mounted filesystem. (Linux permits a filesystem to be mounted at multiple points, but .BR link () does not work across different mount points, even if the same filesystem is mounted on both.) .PP The following additional errors can occur for .BR linkat (): .TP .B EBADF .I olddirfd or .I newdirfd is not a valid file descriptor. .TP .B EINVAL An invalid flag value was specified in .IR flags . .TP .B ENOENT .B AT_EMPTY_PATH was specified in .IR flags , but the caller did not have the .B CAP_DAC_READ_SEARCH capability. .TP .B ENOENT An attempt was made to link to the .I /proc/self/fd/NN file corresponding to a file descriptor created with open(path, O_TMPFILE | O_EXCL, mode); See .BR open (2). .TP .B ENOENT .I oldpath is a relative pathname and .I olddirfd refers to a directory that has been deleted, or .I newpath is a relative pathname and .I newdirfd refers to a directory that has been deleted. .TP .B ENOTDIR .I oldpath is relative and .I olddirfd is a file descriptor referring to a file other than a directory; or similar for .I newpath and .I newdirfd .TP .B EPERM .BR AT_EMPTY_PATH was specified in .IR flags , .I oldpath is an empty string, and .IR olddirfd refers to a directory. .SH VERSIONS .BR linkat () was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4. .SH CONFORMING TO .BR link (): SVr4, 4.3BSD, POSIX.1-2001 (but see NOTES), POSIX.1-2008. .\" SVr4 documents additional ENOLINK and .\" EMULTIHOP error conditions; POSIX.1 does not document ELOOP. .\" X/OPEN does not document EFAULT, ENOMEM or EIO. .BR linkat (): POSIX.1-2008. .SH NOTES Hard links, as created by .BR link (), cannot span filesystems. 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, use .BR linkat (2). .SS Glibc notes On older kernels where .BR linkat () is unavailable, the glibc wrapper function falls back to the use of .BR link (), unless the .B AT_SYMLINK_FOLLOW is specified. When .I oldpath and .I newpath are relative pathnames, glibc constructs pathnames based on the symbolic links in .IR /proc/self/fd that correspond to the .I olddirfd and .IR newdirfd arguments. .SH BUGS On NFS filesystems, 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 open (2), .BR rename (2), .BR stat (2), .BR symlink (2), .BR unlink (2), .BR path_resolution (7), .BR symlink (7) .SH COLOPHON This page is part of release 3.74 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%http://www.kernel.org/doc/man\-pages/.