link(1) manual page

The ln utility creates a new directory entry (linked file) for the file name specified by target_file. The target_file will be created with the same file modes as the source_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 "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.

The options are as follows:

-F

If the target file already exists and is a directory, then remove it so that the link may occur. The -F option should be used with either -f or -i options. If neither -f nor -i is specified, -f is implied. The -F option is a no-op unless -s is specified.

-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 -P option.

-P

When creating a hard link to a symbolic link, create a hard link to the symbolic link itself. This option cancels the -L option.

-f

If the target file already exists, then unlink it so that the link may occur. (The -f option overrides any previous -i and -w options.)

-h

If the target_file or target_dir is a symbolic link, do not follow it. This is most useful with the -f option, to replace a symlink which may point to a directory.

-i

Cause ln to write a prompt to standard error if the target file exists. If the response from the standard input begins with the character 'y' or 'Y', then unlink the target file so that the link may occur. Otherwise, do not attempt the link. (The -i option overrides any previous -f options.)

-n

Same as -h, for compatibility with other ln implementations.

-s

Create a symbolic link.

-v

Cause ln to be verbose, showing files as they are processed.

-w

Warn if the source of a symbolic link does not currently exist.

By default, ln makes 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.

A symbolic link contains the name of the file to which it is linked. The referenced file is used when an open(2) operation is performed on the link. A stat(2) on a symbolic link will return the linked-to file; an lstat(2) must be done to obtain information about the link. The 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.

Given one or two arguments, ln creates a link to an existing file source_file. If target_file is given, the link has that name; 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 source_file.

Given more than two arguments, ln makes links in target_dir to all the named source files. The links made will have the same name as the files being linked to.

When the utility is called as 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 link(2) operation using the two passed arguments.

Create a symbolic link named /home/src and point it to /usr/src:

# ln -s /usr/src /home/src

Hard link /usr/local/bin/fooprog to file /usr/local/bin/fooprog-1.0:

# ln /usr/local/bin/fooprog-1.0 /usr/local/bin/fooprog

As an exercise, try the following commands:

# ls -i /bin/[
11553 /bin/[
# ls -i /bin/test
11553 /bin/test

Note that both files have the same inode; that is, /bin/[ is essentially an alias for the test(1) command. This hard link exists so test(1) may be invoked from shell scripts, for example, using the if [ ] construct.

In the next example, the second call to ln removes the original foo and creates a replacement pointing to baz:

# mkdir bar baz
# ln -s bar foo
# ln -shf baz foo

Without the -h option, this would instead leave foo pointing to bar and inside foo create a new symlink baz pointing to itself. This results from directory-walking.

An easy rule to remember is that the argument order for ln is the same as for cp(1): The first argument needs to exist, the second one is created.

“	… one of the main causes of the fall of the Roman Empire was that, lacking zero, they had no way to indicate successful termination of their C programs.	”
— Robert Firth

Manual Pages — LN

NAME

CONTENTS

SYNOPSIS

DESCRIPTION

EXAMPLES

COMPATIBILITY

SEE ALSO

STANDARDS

HISTORY

-F
	If the target file already exists and is a directory, then remove it so that the link may occur. The -F option should be used with either -f or -i options. If neither -f nor -i is specified, -f is implied. The -F option is a no-op unless -s is specified.
-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 -P option.
-P
	When creating a hard link to a symbolic link, create a hard link to the symbolic link itself. This option cancels the -L option.
-f
	If the target file already exists, then unlink it so that the link may occur. (The -f option overrides any previous -i and -w options.)
-h
	If the target_file or target_dir is a symbolic link, do not follow it. This is most useful with the -f option, to replace a symlink which may point to a directory.
-i
	Cause ln to write a prompt to standard error if the target file exists. If the response from the standard input begins with the character '`y`' or '`Y`', then unlink the target file so that the link may occur. Otherwise, do not attempt the link. (The -i option overrides any previous -f options.)
-n
	Same as -h, for compatibility with other ln implementations.
-s
	Create a symbolic link.
-v
	Cause ln to be verbose, showing files as they are processed.
-w
	Warn if the source of a symbolic link does not currently exist.