There are two concepts of `link' in Unix, usually called hard link and soft
link. A hard link is just a name for a file. (And a file can have several
names. It is deleted from disk only when the last name is removed. The number
of names is given by ls(1). There is no such thing as an `original'
name: all names have the same status. Usually, but not necessarily, all names
of a file are found in the filesystem that also contains its data.)
A soft link (or symbolic link, or symlink) is an entirely different animal: it
is a small special file that contains a pathname. Thus, soft links can point
at files on different filesystems (possibly NFS mounted from different
machines), and need not point to actually existing files. When accessed (with
the open(2) or stat(2) system calls), a reference to a symlink
is replaced by the operating system kernel with a reference to the file named
by the path name. (However, with rm(1) and unlink(2) the link
itself is removed, not the file it points to. There are special system calls
lstat(2) and readlink(2) that read the status of a symlink and
the filename it points to. For various other system calls there is some
uncertainty and variation between operating systems as to whether the
operation acts on the symlink itself, or on the file pointed to.)
ln makes links between files. By default, it makes hard links; with the
-s option, it makes symbolic (or `soft') links.
If only one file is given, it links that file into the current directory, that
is, creates a link to that file in the current directory, with name equal to
(the last component of) the name of that file. (This is a GNU extension.)
Otherwise, if the last argument names an existing directory, ln will
create links to each mentioned source file in that directory, with a
name equal to (the last component of) the name of that source file.
(But see the description of the --no-dereference option below.)
Otherwise, if only two files are given, it creates a link named dest to
the file source. It is an error if the last argument is not a directory
and more than two files are given.
By default, ln does not remove existing files or existing symbolic links.
(Thus, it can be used for locking purposes: it will succeed only if
dest did not exist already.) But it can be forced to do so with the
On existing implementations, if it is at all possible to make a hard link to a
directory, this may be done by the superuser only. POSIX forbids the system
call link(2) and the utility ln to make hard links to
directories (but does not forbid hard links to cross filesystem boundaries).
Allow the super-user to make hard links to
Remove existing destination files.
Prompt whether to remove existing destination files.
When given an explicit destination that is a symlink to a
directory, treat that destination as if it were a normal file.
When the destination is an actual directory (not a symlink to one), there is
no ambiguity. The link is created in that directory. But when the
specified destination is a symlink to a directory, there are two ways to
treat the user's request. ln can treat the destination just as it
would a normal directory and create the link in it. On the other hand, the
destination can be viewed as a non-directory - as the symlink itself. In
that case, ln must delete or backup that symlink before creating
the new link. The default is to treat a destination that is a symlink to a
directory just like a directory.
Make symbolic links instead of hard links. This option
merely produces an error message on systems that do not support symbolic
The GNU versions of programs like cp, mv, ln,
install and patch will make a backup of files about to be
overwritten, changed or destroyed if that is desired. That backup files are
desired is indicated by the -b option. How they should be named is specified
by the -V option. In case the name of the backup file is given by the name of
the file extended by a suffix, this suffix is specified by the -S option.
Make backups of files that are about to be overwritten or
-S SUFFIX, --suffix=SUFFIX
Append SUFFIX to each backup file made. If this
option is not specified, the value of the SIMPLE_BACKUP_SUFFIX
environment variable is used. And if SIMPLE_BACKUP_SUFFIX is not
set, the default is `~'.
Specify how backup files are named. The
METHOD argument can be `numbered' (or `t'), `existing' (or `nil'), or
`never' (or `simple'). If this option is not specified, the value of the
VERSION_CONTROL environment variable is used. And if
VERSION_CONTROL is not set, the default backup type is `existing'.
This option corresponds to the Emacs variable `version-control'. The valid
METHODs are (unique abbreviations are accepted):
Always make numbered backups.
Make numbered backups of files that already have them,
simple backups of the others.