path: root/bin/ln/ln.1

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.\"
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.\"	@(#)ln.1	8.2 (Berkeley) 12/30/93
.\"
.Dd $Mdocdate: September 16 2007 $
.Dt LN 1
.Os
.Sh NAME
.Nm ln
.Nd make hard and symbolic links to files
.Sh SYNOPSIS
.Nm ln
.Op Fl fhns
.Ar source
.Op Ar target
.Nm ln
.Op Fl fs
.Ar source ...\&
.Op Ar directory
.Sh DESCRIPTION
The
.Nm
utility creates a new directory entry (linked file) which has the
same modes as the original file.
It is useful for maintaining multiple copies of a file in many places
at once without using up storage for the copies;
instead, a link
.Dq points
to the original copy.
There are two types of links; hard links and symbolic links.
How a link points
to a file is one of the differences between a hard and symbolic link.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl f
Unlink any already existing file, permitting the link to occur.
.It Fl h
If the target is a symlink to a directory, do not descend into it.
.It Fl n
An alias for
.Fl h
for compatibility with other operating systems.
.It Fl s
Create a symbolic link.
.El
.Pp
By default,
.Nm
makes
.Dq hard
links.
A hard link to a file is indistinguishable from the original directory entry;
any changes to a file are effectively 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, refer to directories, and refer to
non-existent files.
.Pp
Given one or two arguments,
.Nm
creates a link to an existing file
.Ar source .
If
.Ar target
is given, the link has that name;
.Ar target
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 .
.Pp
Given more than two arguments,
.Nm
makes links in
.Ar directory
to all the named source files.
The links made will have the same name as the files being linked to.
.Pp
The
.Nm
utility exits 0 on success or >0 if an error occurred.
.Sh EXAMPLES
Create a symbolic link named
.Pa /home/www
and point it to
.Pa /var/www :
.Pp
.Dl # ln -s /var/www /home/www
.Pp
Hard link
.Pa /usr/local/bin/fooprog
to file
.Pa /usr/local/bin/fooprog-1.0 :
.Pp
.Dl # ln /usr/local/bin/fooprog-1.0 /usr/local/bin/fooprog
.Pp
As an exercise, try the following commands:
.Bd -literal -offset indent
$ ls -i /bin/[
11553 /bin/[
$ ls -i /bin/test
11553 /bin/test
.Ed
.Pp
Note that both files have the same inode; that is,
.Pa /bin/[
is essentially an alias for the
.Xr test 1
command.
This hard link exists so
.Xr test 1
may be invoked from shell scripts, for example, using the
.Li "if [ ]"
construct.
.Pp
In the next example, the second call to
.Nm
removes the original
.Pa foo
and creates a replacement pointing to
.Pa baz :
.Bd -literal -offset indent
$ mkdir bar baz
$ ln -s bar foo
$ ln -shf baz foo
.Ed
.Pp
Without the
.Fl h
option, this would instead leave
.Pa foo
pointing to
.Pa bar
and inside
.Pa foo
create a new symlink
.Pa baz
pointing to itself.
This results from directory-walking.
.Sh SEE ALSO
.Xr link 2 ,
.Xr lstat 2 ,
.Xr readlink 2 ,
.Xr stat 2 ,
.Xr symlink 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2004
specification.
.Pp
The flags
.Op Fl hn
are extensions to that specification.
.Sh HISTORY
An
.Nm
utility appeared in
.At v3 .
.Sh CAVEATS
Since the
.Ar source
file must have its link count incremented, a hard link cannot be created to a
file which is flagged immutable or append-only (see
.Xr chflags 1 ) .