248 lines
6.2 KiB
Groff
248 lines
6.2 KiB
Groff
.\" $NetBSD: link.2,v 1.33 2019/09/01 19:52:32 sevan Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993, 2011
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)link.2 8.3 (Berkeley) 1/12/94
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.\"
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.Dd September 1, 2019
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.Dt LINK 2
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.Os
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.Sh NAME
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.Nm link
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.Nd make a hard file link
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn link "const char *name1" "const char *name2"
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.In fcntl.h
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.Ft int
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.Fn linkat "int fd1" "const char *name1" "int fd2" "const char *name2" "int flags"
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.Sh DESCRIPTION
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The
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.Fn link
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function call
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atomically creates the specified directory entry (hard link)
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.Fa name2
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with the attributes of the underlying object pointed at by
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.Fa name1 .
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If the link is successful: the link count of the underlying object
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is incremented;
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.Fa name1
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and
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.Fa name2
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share equal access and rights
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to the
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underlying object.
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.Pp
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If
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.Fa name1
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is removed, the file
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.Fa name2
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is not deleted and the link count of the
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underlying object is
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decremented.
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.Pp
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.Fa name1
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must exist for the hard link to
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succeed and
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both
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.Fa name1
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and
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.Fa name2
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must be in the same file system.
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.Fa name1
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may not be a directory unless the caller is the super-user
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and the file system containing it supports linking to directories.
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.Pp
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.Fn linkat
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works the same way as
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.Fn link
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except if
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.Fa name1
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(resp.
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.Fa name2 )
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is relative.
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In that case, it is looked up from a directory whose file
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descriptor was passed as
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.Fa fd1
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(resp.
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.Fa fd2 ) .
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Search permission is required on the directories named by
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.Fa fd1
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and
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.Fa fd2 .
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.\" (These alternatives await a decision about the semantics of O_SEARCH)
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.\" Search permission is required on the directories named by
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.\" .Fa fd1
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.\" and
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.\" .Fa fd2
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.\" unless they were opened with the
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.\" .Dv O_SEARCH
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.\" flag.
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.\" - or -
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.\" The directories named by
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.\" .Fa fd1
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.\" and
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.\" .Fa fd2
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.\" must have been opened with the
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.\" .Dv O_SEARCH
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.\" flag.
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.Fa fd1
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or
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.Fa fd2
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can be set to
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.Dv AT_FDCWD
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in order to specify the current directory.
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.Pp
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When operating on a symlink,
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.Fn link
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resolves the symlink and creates a hard link on the target.
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.Fn linkat
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will do the same if
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.Dv AT_SYMLINK_FOLLOW
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is set in
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.Fa flags ,
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but it will link on the symlink itself if the flag is clear.
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.Sh RETURN VALUES
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.Rv -std link linkat
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.Sh ERRORS
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.Fn link
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and
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.Fn linkat
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will fail and no link will be created if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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A component of either path prefix denies search permission, or
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the requested link requires writing in a directory with a mode
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that denies write permission.
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.It Bq Er EDQUOT
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The directory in which the entry for the new link
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is being placed cannot be extended because the
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user's quota of disk blocks on the file system
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containing the directory has been exhausted.
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.It Bq Er EEXIST
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The link named by
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.Fa name2
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does exist.
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.It Bq Er EFAULT
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One of the pathnames specified
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is outside the process's allocated address space.
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.It Bq Er EIO
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An I/O error occurred while reading from or writing to
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the file system to make the directory entry.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating one of the pathnames.
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.It Bq Er EMLINK
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The link count of the file named by
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.Fa name1
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would exceed
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.Brq Dv LINK_MAX .
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded
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.Brq Dv NAME_MAX
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characters, or an entire path name exceeded
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.Brq Dv PATH_MAX
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characters.
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.It Bq Er ENOENT
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A component of either path prefix does not exist, or the file named
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by
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.Fa name1
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does not exist.
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.It Bq Er ENOSPC
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The directory in which the entry for the new link is being placed
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cannot be extended because there is no space left on the file
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system containing the directory.
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.It Bq Er ENOTDIR
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A component of either path prefix is not a directory.
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.It Bq Er EOPNOTSUPP
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The file system containing the file named by
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.Fa name1
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does not support links.
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.It Bq Er EPERM
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The file named by
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.Fa name1
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is a directory and the effective
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user ID is not super-user,
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or the file system containing the file does not permit the use of
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.Fn link
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on a directory.
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.It Bq Er EROFS
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The requested link requires writing in a directory on a read-only file
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system.
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.It Bq Er EXDEV
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The link named by
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.Fa name2
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and the file named by
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.Fa name1
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are on different file systems.
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.El
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.Pp
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In addition,
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.Fn linkat
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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.Fa name1
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or
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.Fa name2
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does not specify an absolute path and
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.Fa fd1
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or
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.Fa fd2 ,
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respectively, is neither
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.Dv AT_FDCWD
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nor a valid file descriptor open for reading or searching.
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.It Bq Er ENOTDIR
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.Fa name1
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or
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.Fa name2
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is not an absolute path and
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.Fa fd1
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or
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.Fa fd2 ,
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respectively, is a file descriptor associated with a non-directory file.
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.El
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.Sh SEE ALSO
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.Xr symlink 2 ,
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.Xr unlink 2
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.Sh STANDARDS
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The
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.Fn link
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function conforms to
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.St -p1003.1-90 .
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.Fn linkat
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conforms to
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.St -p1003.1-2008 .
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.Sh HISTORY
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The
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.Fn link
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function appeared in
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.At v1 .
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