230 lines
5.9 KiB
Groff
230 lines
5.9 KiB
Groff
.\" $OpenBSD: ln.1,v 1.33 2016/08/10 19:46:43 schwarze Exp $
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.\" $NetBSD: ln.1,v 1.10 1995/07/25 19:37:04 jtc Exp $
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.\"
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.\" Copyright (c) 1980, 1990, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the Institute of Electrical and Electronics Engineers, Inc.
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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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.\" @(#)ln.1 8.2 (Berkeley) 12/30/93
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.\"
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.Dd $Mdocdate: August 10 2016 $
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.Dt LN 1
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.Os
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.Sh NAME
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.Nm ln
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.Nd make hard and symbolic links to files
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.Sh SYNOPSIS
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.Nm ln
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.Op Fl fhLnPs
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.Ar source
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.Op Ar target
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.Nm ln
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.Op Fl fLPs
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.Ar source ...
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.Op Ar directory
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.Sh DESCRIPTION
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The
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.Nm
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utility creates a new directory entry (linked file) which has the
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same modes as the original file.
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It is useful for maintaining multiple copies of a file in many places
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at once without using up storage for the copies;
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instead, a link
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.Dq points
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to the original copy.
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There are two types of links: hard links and symbolic links.
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How a link points
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to a file is one of the differences between a hard and symbolic link.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl f
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Unlink any already existing file, permitting the link to occur.
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.It Fl h
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If the target is a symlink to a directory, do not descend into it.
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.It Fl L
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When creating a hard link and the source is a symbolic link,
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link to the fully resolved target of the symbolic link.
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This is the default.
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The
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.Fl L
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option overrides any previous
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.Fl P
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options.
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.It Fl n
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An alias for
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.Fl h
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for compatibility with other operating systems.
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.It Fl P
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When creating a hard link and the source is a symbolic link,
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link to the symbolic link itself.
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The
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.Fl P
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option overrides any previous
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.Fl L
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options.
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.It Fl s
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Create a symbolic link.
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.El
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.Pp
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By default,
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.Nm
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makes
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.Dq hard
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links.
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A hard link to a file is indistinguishable from the original directory entry;
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any changes to a file are effectively independent of the name used to reference
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the file.
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Hard links may not normally refer to directories and may not span file systems.
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.Pp
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A symbolic link contains the name of the file to
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which it is linked.
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The referenced file is used when an
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.Xr open 2
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operation is performed on the link.
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A
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.Xr stat 2
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on a symbolic link will return the linked-to file; an
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.Xr lstat 2
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must be done to obtain information about the link.
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The
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.Xr readlink 2
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call may be used to read the contents of a symbolic link.
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Symbolic links may span file systems, refer to directories, and refer to
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non-existent files.
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.Pp
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Given one or two arguments,
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.Nm
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creates a link to an existing file
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.Ar source .
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If
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.Ar target
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is given, the link has that name;
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.Ar target
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may also be a directory in which to place the link.
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Otherwise, it is placed in the current directory.
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If only the directory is specified, the link will be made
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to the last component of
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.Ar source .
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.Pp
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Given more than two arguments,
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.Nm
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makes links in
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.Ar directory
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to all the named source files.
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The links made will have the same name as the files being linked to.
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.Sh EXIT STATUS
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.Ex -std ln
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.Sh EXAMPLES
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Create a symbolic link named
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.Pa /home/www
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and point it to
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.Pa /var/www :
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.Pp
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.Dl # ln -s /var/www /home/www
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.Pp
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Hard link
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.Pa /usr/local/bin/fooprog
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to file
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.Pa /usr/local/bin/fooprog-1.0 :
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.Pp
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.Dl # ln /usr/local/bin/fooprog-1.0 /usr/local/bin/fooprog
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.Pp
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As an exercise, try the following commands:
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.Bd -literal -offset indent
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$ ls -i /bin/[
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11553 /bin/[
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$ ls -i /bin/test
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11553 /bin/test
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.Ed
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.Pp
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Note that both files have the same inode; that is,
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.Pa /bin/[
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is essentially an alias for the
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.Xr test 1
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command.
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This hard link exists so
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.Xr test 1
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may be invoked from shell scripts, for example, using the
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.Li "if [ ]"
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construct.
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.Pp
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In the next example, the second call to
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.Nm
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removes the original
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.Pa foo
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and creates a replacement pointing to
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.Pa baz :
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.Bd -literal -offset indent
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$ mkdir bar baz
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$ ln -s bar foo
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$ ln -shf baz foo
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.Ed
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.Pp
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Without the
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.Fl h
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option, this would instead leave
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.Pa foo
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pointing to
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.Pa bar
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and inside
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.Pa foo
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create a new symlink
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.Pa baz
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pointing to itself.
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This results from directory-walking.
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.Sh SEE ALSO
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.Xr linkat 2 ,
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.Xr lstat 2 ,
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.Xr readlink 2 ,
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.Xr stat 2 ,
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.Xr symlink 2 ,
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.Xr symlink 7
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.Sh STANDARDS
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The
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.Nm
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utility is compliant with the
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.St -p1003.1-2008
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specification.
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.Pp
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The flags
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.Op Fl hn
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are extensions to that specification.
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.Sh HISTORY
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An
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.Nm
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utility appeared in
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.At v1 .
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.Sh CAVEATS
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Since the
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.Ar source
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file must have its link count incremented, a hard link cannot be created to a
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file which is flagged immutable or append-only (see
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.Xr chflags 1 ) .
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