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12.2 ln: Make links between files

ln makes links between files. By default, it makes hard links; with the -s option, it makes symbolic (or soft) links. Synopses:

     ln [option]... [-T] target linkname
     ln [option]... target
     ln [option]... target... directory
     ln [option]... -t directory target...

Normally ln does not remove existing files. Use the --force (-f) option to remove them unconditionally, the --interactive (-i) option to remove them conditionally, and the --backup (-b) option to rename them.

A hard link is another name for an existing file; the link and the original are indistinguishable. Technically speaking, they share the same inode, and the inode contains all the information about a file—indeed, it is not incorrect to say that the inode is the file. Most systems prohibit making a hard link to a directory; on those where it is allowed, only the super-user can do so (and with caution, since creating a cycle will cause problems to many other utilities). Hard links cannot cross file system boundaries. (These restrictions are not mandated by POSIX, however.)

Symbolic links (symlinks for short), on the other hand, are a special file type (which not all kernels support: System V release 3 (and older) systems lack symlinks) in which the link file actually refers to a different file, by name. When most operations (opening, reading, writing, and so on) are passed the symbolic link file, the kernel automatically dereferences the link and operates on the target of the link. But some operations (e.g., removing) work on the link file itself, rather than on its target. The owner and group of a symlink are not significant to file access performed through the link, but do have implications on deleting a symbolic link from a directory with the restricted deletion bit set. On the GNU system, the mode of a symlink has no significance and cannot be changed, but on some BSD systems, the mode can be changed and will affect whether the symlink will be traversed in file name resolution. See Symbolic Links.

Symbolic links can contain arbitrary strings; a dangling symlink occurs when the string in the symlink does not resolve to a file. There are no restrictions against creating dangling symbolic links. There are trade-offs to using absolute or relative symlinks. An absolute symlink always points to the same file, even if the directory containing the link is moved. However, if the symlink is visible from more than one machine (such as on a networked file system), the file pointed to might not always be the same. A relative symbolic link is resolved in relation to the directory that contains the link, and is often useful in referring to files on the same device without regards to what name that device is mounted on when accessed via networked machines.

When creating a relative symlink in a different location than the current directory, the resolution of the symlink will be different than the resolution of the same string from the current directory. Therefore, many users prefer to first change directories to the location where the relative symlink will be created, so that tab-completion or other file resolution will find the same target as what will be placed in the symlink.

The program accepts the following options. Also see Common options.

-b
--backup[=method]
See Backup options. Make a backup of each file that would otherwise be overwritten or removed.
-d
-F
--directory
Allow users with appropriate privileges to attempt to make hard links to directories. However, note that this will probably fail due to system restrictions, even for the super-user.
-f
--force
Remove existing destination files.
-i
--interactive
Prompt whether to remove existing destination files.
-L
--logical
If -s is not in effect, and the source file is a symbolic link, create the hard link to the file referred to by the symbolic link, rather than the symbolic link itself.
-n
--no-dereference
Do not treat the last operand specially when it is a symbolic link to a directory. Instead, treat it 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.

This option is weaker than the --no-target-directory (-T) option, so it has no effect if both options are given.

-P
--physical
If -s is not in effect, and the source file is a symbolic link, create the hard link to the symbolic link itself. On platforms where this is not supported by the kernel, this option creates a symbolic link with identical contents; since symbolic link contents cannot be edited, any file name resolution performed through either link will be the same as if a hard link had been created.
-r
--relative
Make symbolic links relative to the link location.

Example:

          ln -srv /a/file /tmp
          '/tmp/file' -> '../a/file'

Relative symbolic links are generated based on their canonicalized containing directory, and canonicalized targets. I.E. all symbolic links in these file names will be resolved. See realpath invocation, which gives greater control over relative file name generation, as demonstrated in the following example:

     
          ln--relative() {
            test "$1" = --no-symlinks && { nosym=$1; shift; }
            target="$1";
            test -d "$2" && link="$2/." || link="$2"
            rtarget="$(realpath $nosym -m "$target" \
                        --relative-to "$(dirname "$link")")"
            ln -s -v "$rtarget" "$link"
          }
     

-s
--symbolic
Make symbolic links instead of hard links. This option merely produces an error message on systems that do not support symbolic links.
-S suffix
--suffix=suffix
Append suffix to each backup file made with -b. See Backup options.
-t directory
--target-directory=directory
Specify the destination directory. See Target directory.
-T
--no-target-directory
Do not treat the last operand specially when it is a directory or a symbolic link to a directory. See Target directory.
-v
--verbose
Print the name of each file after linking it successfully.

If -L and -P are both given, the last one takes precedence. If -s is also given, -L and -P are silently ignored. If neither option is given, then this implementation defaults to -P if the system link supports hard links to symbolic links (such as the GNU system), and -L if link follows symbolic links (such as on BSD).

An exit status of zero indicates success, and a nonzero value indicates failure.

Examples:

     Bad Example:
     
     # Create link ../a pointing to a in that directory.
     # Not really useful because it points to itself.
     ln -s a ..
     
     Better Example:
     
     # Change to the target before creating symlinks to avoid being confused.
     cd ..
     ln -s adir/a .
     
     Bad Example:
     
     # Hard coded file names don't move well.
     ln -s $(pwd)/a /some/dir/
     
     Better Example:
     
     # Relative file names survive directory moves and also
     # work across networked file systems.
     ln -s afile anotherfile
     ln -s ../adir/afile yetanotherfile