HardenedBSD/bin/ln/ln.1

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.Dd June 12, 2017
.Dt LN 1
.Os
.Sh NAME
.Nm ln ,
.Nm link
.Nd link files
.Sh SYNOPSIS
.Nm
.Op Fl L | Fl P | Fl s Op Fl F
.Op Fl f | iw
.Op Fl hnv
.Ar source_file
.Op Ar target_file
.Nm
.Op Fl L | Fl P | Fl s Op Fl F
.Op Fl f | iw
.Op Fl hnv
.Ar source_file ...
.Ar target_dir
.Nm link
.Ar source_file Ar target_file
.Sh DESCRIPTION
The
.Nm
utility creates a new directory entry (linked file) for the file name
specified by
.Ar target_file .
The
.Ar target_file
will be created with the same file modes as the
.Ar source_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 and symbolic link.
.Pp
The options are as follows:
.Bl -tag -width flag
.It Fl F
If the target file already exists and is a directory, then remove it
so that the link may occur.
The
.Fl F
option should be used with either
.Fl f
or
.Fl i
options.
If neither
.Fl f
nor
.Fl i
is specified,
.Fl f
is implied.
The
.Fl F
option is a no-op unless
.Fl s
is specified.
.It Fl L
When creating a hard link to a symbolic link,
create a hard link to the target of the symbolic link.
This is the default.
This option cancels the
.Fl P
option.
.It Fl P
When creating a hard link to a symbolic link,
create a hard link to the symbolic link itself.
This option cancels the
.Fl L
option.
.It Fl f
If the target file already exists,
then unlink it so that the link may occur.
(The
.Fl f
option overrides any previous
.Fl i
and
.Fl w
options.)
.It Fl h
If the
.Ar target_file
or
.Ar target_dir
is a symbolic link, do not follow it.
This is most useful with the
.Fl f
option, to replace a symlink which may point to a directory.
.It Fl i
Cause
.Nm
to write a prompt to standard error if the target file exists.
If the response from the standard input begins with the character
.Sq Li y
or
.Sq Li Y ,
then unlink the target file so that the link may occur.
Otherwise, do not attempt the link.
(The
.Fl i
option overrides any previous
.Fl f
options.)
.It Fl n
Same as
.Fl h ,
for compatibility with other
.Nm
implementations.
.It Fl s
Create a symbolic link.
.It Fl v
Cause
.Nm
to be verbose, showing files as they are processed.
.It Fl w
Warn if the source of a symbolic link does not currently exist.
.El
.Pp
By default,
.Nm
makes
.Em 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.
Directories may not be hardlinked, and hard links 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
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
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.
.Pp
When the utility is called as
.Nm link ,
exactly two arguments must be supplied,
neither of which may specify a directory.
No options may be supplied in this simple mode of operation,
which performs a
.Xr link 2
operation using the two passed arguments.
.Sh EXAMPLES
Create a symbolic link named
.Pa /home/src
and point it to
.Pa /usr/src :
.Pp
.Dl # ln -s /usr/src /home/src
.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.
.Pp
An easy rule to remember is that the argument order for
.Nm
is the same as for
.Xr cp 1 :
The first argument needs to exist, the second one is created.
.Sh COMPATIBILITY
The
.Fl h ,
.Fl i ,
.Fl n ,
.Fl v
and
.Fl w
options are non-standard and their use in scripts is not recommended.
They are provided solely for compatibility with other
.Nm
implementations.
.Pp
The
.Fl F
option is a
.Fx
extension and should not be used in portable scripts.
.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 conforms to
.St -p1003.2-92 .
.Pp
The simplified
.Nm link
command conforms to
.St -susv2 .
.Sh HISTORY
An
.Nm
command appeared in
.At v1 .