usr/src/bin/ln/ln.1

.\" Copyright (c) 1980, 1990 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Institute of Electrical and Electronics Engineers, Inc.
.\"
.\" %sccs.include.redist.roff%
.\"
.\"     @(#)ln.1        6.9 (Berkeley) %G%
.\"
.Dd
.Dt LN 1
.Os BSD 4
.Sh NAME
.Nm ln
.Nd make links
.Sh SYNOPSIS
.Nm ln
.Op Fl fs
.Ar source_file
.Op target_file
.Nm ln
.Op Fl fs
.Ar source_file ...
.Op target_dir
.Sh DESCRIPTION
The
.Nm ln
utility creates a new directory entry (linked file) which has the
same modes as the orginal file.
It is useful for maintaining multiple copies of a file in many places
at once without using up storage for the
.Dq copies ;
instead, a link
.Dq points
to the original copy.
There are two types of links; hard links and symbolic links.
How a link
.Dq points
to a file is one of the differences between a hard or symbolic link.
.Pp
The options are as follows:
.Bl -tag -width flag
.It Fl f
Unlink any already existing file, permitting the link to occur.
.It Fl s
Create a symbolic link.
.El
.Pp
By default
.Nm ln
makes
.Em hard
links.
A hard link to a file is indistinguishable from the original directory entry;
any changes to a file are effective independent of the name used to reference
the file.
Hard links may not normally refer to directories and may not span file systems.
.Pp
A symbolic link contains the name of the file to
which it is linked.  The referenced file is used when an
.Xr open  2
operation is performed on the link.
A
.Xr stat  2
on a symbolic link will return the linked-to file; an
.Xr lstat  2
must be done to obtain information about the link.
The
.Xr readlink  2
call may be used to read the contents of a symbolic link.
Symbolic links may span file systems and may refer to directories.
.Pp
Given one or two arguments,
.Nm ln
creates a link to an existing file
.Ar source_file  .
If
.Ar target_file
is given, the link has that name;
.Ar target_file
may also be a directory in which to place the link;
otherwise it is placed in the current directory.
If only the directory is specified, the link will be made
to the last component of
.Ar source_file  .
.Pp
Given more than two arguments,
.Nm ln
makes links in
.Ar target_dir
to all the named source files.
The links made will have the same name as the files being linked to.
.Sh SYMBOLIC LINK FOLLOWING
Many file system traversal utilities and system calls
have the option of traversing the file system in a physical traversal, i.e.,
treating a symbolic link as a link rather than its target, or in a logical
traversal, i.e., following the symbolic link whenever one is encountered.
The following rules summarize the conventions of symbolic link following in
utilities and system calls.
.Pp
The only system calls that operate on symbolic links are
.Xr unlink 2 ,
.Xr rename 2 ,
.Xr lstat 2 ,
and
.Xr readlink 2 .
All other system calls follow the symbolic link and operate on the object to
which the link points to.
.Pp
Utilities that do not recurse over trees always
follow symbolic links on the command line.  The rest of the utilities
.Xr (chown 1 ,
.Xr chmod 1 ,
.Xr chgrp 1 ,
.Xr chflags 1 ,
.Xr cp 1 ,
.Xr du 1 ,
.Xr find 1 ,
and
.Xr tar 1 )
treat symbolic links in three distinct ways.  The first option, the default,
is to never follow any symbolic link.  The second, specified by the
.Fl H
flag, causes the utility to follow symbolic links only on the command line
but not in the tree of traversal (if recursive).  The third option, specified
by the
.Fl h
flag, causes the utility to follow any symbolic link encountered on the command
line and in the tree of traversal (if recursive).
.Pp
The purpose of the
.Fl H
flag is to make the command line name space look like the logical name space,
i.e., make all names on the command line appear as hard links, whereas the
purpose of the
.Fl h
flag is to make the entire hierarchy look like the logical name space. i.e.,
make all names in the hierarchy appear as hard links.
.Pp
Exceptions to these rules are the behaviors of
.Xr rm  1 ,
.Xr mv 1 ,
and
.Xr ls  1 .
.Pp
.Xr Rm 1
and
.Xr mv 1
operate on the name, not the object it points to, and therefore always operate
on the symbolic link itself and do not follow it.
.Pp
For historical reasons,
.Xr ls 1
follows symbolic links in the entire hierarchy (including command line)
only when the
.Fl L
option is specified, and follows only on the command line only
when neither of the
.Fl F, d,
or
.Fl l
options are specified. In all other cases,
.Xr ls 1
does not follow symbolic links.
.Sh SEE ALSO
.Xr rm 1 ,
.Xr cp 1 ,
.Xr mv 1 ,
.Xr ls 1 ,
.Xr tar 1 ,
.Xr chown 1 ,
.Xr chmod 1 ,
.Xr chgrp 1 ,
.Xr chflags 1 ,
.Xr du 1 ,
.Xr find 1 ,
.Xr link 2 ,
.Xr readlink 2 ,
.Xr stat 2 ,
.Xr symlink 2
.Sh HISTORY
A
.Nm ln
command appeared in
.At v6 .