.\" This manpage is Copyright (C) 1992 Drew Eckhardt; .\" and Copyright (C) 1993 Michael Haardt, Ian Jackson. .\" and Copyright (C) 2006, 2014 Michael Kerrisk .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .\" 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 2024-05-02 "Linux man-pages 6.8" .SH NAME link, linkat \- make a new name for a file .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B #include <unistd.h> .P .BI "int link(const char *" oldpath ", const char *" newpath ); .P .BR "#include <fcntl.h> " "/* Definition of " AT_* " constants */" .B #include <unistd.h> .P .BI "int linkat(int " olddirfd ", const char *" oldpath , .BI " int " newdirfd ", const char *" newpath ", int " flags ); .fi .P .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .P .BR linkat (): .nf Since glibc 2.10: _POSIX_C_SOURCE >= 200809L Before glibc 2.10: _ATFILE_SOURCE .fi .SH DESCRIPTION .BR link () creates a new link (also known as a hard link) to an existing file. .P If .I newpath exists, it will .I not be overwritten. .P 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. .P 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). .P 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 ()). .P If .I oldpath is absolute, then .I olddirfd is ignored. .P 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 . .P 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 .I 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 except a directory. This will generally not work if the file has a link count of zero (files created with .B O_TMPFILE and without .B O_EXCL are an exception). The caller must have the .B 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: .IP .in +4n .EX linkat(AT_FDCWD, "/proc/self/fd/<fd>", newdirfd, newname, AT_SYMLINK_FOLLOW); .EE .in .P Before Linux 2.6.18, the .I flags argument was unused, and had to be specified as 0. .P 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 to indicate the error. .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. For example, on an .BR ext4 (5) filesystem that does not employ the .I dir_index feature, the limit on the number of hard links to a file is 65,000; on .BR btrfs (5), the limit is 65,535 links. .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 .I /proc/sys/fs/protected_hardlinks in .BR proc (5)). .TP .B EPERM .I oldpath is marked immutable or append-only. (See .BR ioctl_iflags (2).) .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 mounts, even if the same filesystem is mounted on both.) .P The following additional errors can occur for .BR linkat (): .TP .B EBADF .I oldpath .RI ( newpath ) is relative but .I olddirfd .RI ( newdirfd ) is neither .B AT_FDCWD nor 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 .IP .in +4n .EX open(path, O_TMPFILE | O_EXCL, mode); .EE .in .IP See .BR open (2). .TP .B ENOENT An attempt was made to link to a .I /proc/self/fd/NN file corresponding to a file that has been deleted. .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 .B AT_EMPTY_PATH was specified in .IR flags , .I oldpath is an empty string, and .I olddirfd refers to a directory. .SH VERSIONS POSIX.1-2001 says that .BR link () should dereference .I oldpath if it is a symbolic link. However, since Linux 2.0, .\" more precisely: since Linux 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 (). .SS glibc 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 .I /proc/self/fd that correspond to the .I olddirfd and .I newdirfd arguments. .SH STANDARDS .TP .BR link () POSIX.1-2008. .SH HISTORY .TP .BR link () SVr4, 4.3BSD, POSIX.1-2001 (but see VERSIONS). .\" SVr4 documents additional ENOLINK and .\" EMULTIHOP error conditions; POSIX.1 does not document ELOOP. .\" X/OPEN does not document EFAULT, ENOMEM or EIO. .TP .BR linkat () POSIX.1-2008. Linux 2.6.16, glibc 2.4. .SH NOTES Hard links, as created by .BR link (), cannot span filesystems. Use .BR symlink (2) if this is required. .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)